Potting Soil Poison

Gardeners often struggle to grow plants in containers. You may feel that you have a really black thumb at times when newly planted seedlings fall over dead or fail to thrive. The problem may not be disease or poor gardening acumen but rather your container media otherwise sold as “Potting Soil”. A trip to one of the big box stores or a larger retail nursery will offer gardeners many choices of bagged potting soils. They are marketed to give you the impression they will grow anything and everything. But do they?
Over the last couple of decades I have done comparative potting media trials where I plant small plugs (usually impatiens) three per six inch container. I go out and find every retail brand of potting mix I can find and plant them all up and then follow them for about two months. I’ve been thinking of revisiting the studies and seeing if anything has changed. I also want to test the assumption that you can’t predict the grow ability of a potting soil by reading the ingredient label as some research suggests. While there can always be a surprise with any given product, I think that from my many trials I can make some suggestions to improve the outcome of your gardening adventures in containers.

Soil on the left has no nutrients same soil on the right with 2 grams of ammonium sulfate added on the surface of the medium one time.

Growing media is not the same as soil. Since media are placed in containers, often plastic ones, they need to be very porous. Porosity of up to 50% is not uncommon in container media. The bulk of the media needs to hold water and minerals for plant growth. Usually an organic material that has a high cation exchange capacity is used. The darling of potting mixes has been Peat Moss. Since peat moss harvesting is damaging to the environment (see previous blog by Linda CS), many gardeners may want to avoid media with peat moss. Bulking agents that do not hold much water or nutrients are also added to “lighten” or aerate the medium. Horticultural perlite (expanded volcanic glass) is the most common. Sand is also sometimes used but it adds weight to the bag and is not preferred by manufacturers. Some media use bark or other wood products to provide greater porosity.
There are usually about 18 to 20 different media on the market at any given time and the results of growing plants in them is predictable. About 10 of the media will not grow anything very well, 5 give ok results and about 5 of the products will grow a nice plant. A lot of the reason for success or lack thereof is about nitrogen chemistry. If no fertilizer is added, the medium will likely not grow well. You can add your own fertilizer and make about  ½ of these poor growing media work. One quarter to one half a teaspoon (approximately 2gm) of ammonium sulfate usually peps up most media that are ok but lack nutrients.  This is an amount used in a standard height 6inch (15cm) diameter plastic container.  Larger containers and plants will require incrementally more fertilizer to achieve growth goals. 
Some media will not grow even when fertilized. This is because they may contain manures, or composts and manures that have added too much salt to the medium. Adding fertilizers to these products only makes them less growable. Sometimes these potting soils will improve with leaching but then fertilizer will need to be added back later to make up for what was leached away. Generally a salty potting mix is worth avoiding.
So how can you tell if you are getting a good or bad mix. You can start by reading the ingredient list. And you will need to decode that list to help you make some decisions. What manufacturers call things can be very misleading. Look for a medium that has fertilizer added and lists what kind of fertilizer was used. These media usually grow without help. Avoid media that use manures, they are not suitable container media ingredients.

Some potting soils claim they can grow plants bigger than others, some claim to be all organic and some claim to be friendly to the earth. This is all marketing. Look for a simple ingredient list that is fortified with a nutrient charge (fertilizer). Begin there. You may want to sieve the medium to remove large particles if you are growing seeds, add more bulking agent (bark, sand, perlite, pumice) for plants that need increased porosity such as orchids, bromeliads and cactus. Don’t be afraid to modify potting mixes to suit the needs you might have. If plants don’t grow, consider adding more nutrients. After growing for some time (months to years), many media will breakdown, and the plant will need to be repotted in a new medium.

When Good Seeds Go Bad: How long can you store seeds?

Many gardeners, myself included, have that stash of old seed packets or saved seeds from garden seasons past, just waiting for the right time to be planted. They may be shoved in a drawer, a box, or in the fridge/freezer. Maybe you’re pulling some out of storage to start this spring – will they even germinate? Are those seeds good indefinitely? Do they ever expire? The answer to that really depends on what plant it is and how they are stored. While there isn’t a date where all the seeds go bad, they will eventually go bad over time. Why is this? And how can I make sure to use my seeds before they’re gone? Let’s find out!

Why Good Seeds Go Bad
While we think of seeds as perhaps inert, dormant, or in stasis they’re still very much alive and therefore are still undergoing processes like respiration, though at a much lower rate than a growing plant. During respiration, the seed (and plant within) are converting the stored sugars and starches in the endosperm to release energy. Once the germination process starts with the imbibition of water, the respiration rate increases drastically. A large amount of stored energy is needed to get through germination and sustain the seedling until it has its first set of true leaves and can photosynthesize on its own.

Seeds need to retain enough stored energy to sustain seedlings until they develop their first leaves and start photosynthesizing.

The shelf life of seeds is determined by the amount of energy that is stored, the amount used during storage, and the amount needed from germination to leaf development. This means that there’s a limit to how long a seed can stay in storage. After a while the seed loses viability if it doesn’t have enough energy stores to get it far enough along to photosynthesize on its own or to have that first burst of respiration at the initiation of germination. When searching for resources, keep in mind that viability refers to the ability of the seed to produce a robust seedling while germination refers to breaking of dormancy. The terms are inter-related, but the rates are not necessarily the same.

Some seeds have evolved to sit dormant for a long time, while others have a very short lifespan. It usually turns out that the seeds that last longest in storage are weeds that have evolved to wait long periods of time for an opportunity to germinate. Garden seeds tend to be on the shorter end of the storage time scale. A now 140-year old ongoing experiment at Michigan State University has given some interesting insight. In 1880, William Beal (one of the fathers of horticulture) buried 20 vials full of a variety of seeds (garden and weed) in secret locations around campus. The plan was to dig one up every 5 years and see what germinated. However, after the fist few rounds the cycle was bumped to 20 years. A vial was opened in 2000 and only one species, a weed, still germinated. This year is another germination year – we’ll have to wait and see if the mullein will germinate again this year.

How long will my seeds last?

Data from Nebraska Extension publication.

There are a few good sources that pull data from a variety of sources. The figure below lists some life expectancy times for common vegetable crops published by Nebraska Extension, using two common manuals on seeds as sources. You’ll also find some likes to other data, including average storage times for flowers, herbs, etc. in the references section (while we don’t typically promote commercial sites, the guide from Johnny’s Select Seeds has a good list of plants and has a variety of extension and academic sources listed). Like the MSU experiment, most of this research was done a while ago, but the data is still a good generalization. Most sources say that these time estimates are based on storage in optimal conditions. According to Johnny’s Select Seeds, “The actual storage life will depend upon the viability and moisture content of the seed when initially placed in storage, the specific variety, and the conditions of the storage environment”.

What are these “optimal” conditions? Generally the conditions are low humidity and low temperature. Low humidity ensures that the seed stays dry, avoiding potential initiation of germination. Low temperature reduces the respiration rate, slowing down usage of stored energy and increasing longevity. Optimal temperature for storage is below 42°F (15°C). Relative humidity should be between 20 and 40%.

The relationship between temperature and humidity seems to be inverse – meaning that as storage temperature goes lower, humidity can be higher and vice versa. However, storage times increase as both go down. Many sources state that seed longevity doubles for every one percent drop in humidity or five degree (F) drop in temperature. The relative humidity of the air affects the moisture level in the seeds. Germination usually starts at 25% moisture (and above). Ideal moisture levels for storage range between 8 and 12 percent and levels between 12 and 25 can lead to degradation of seeds, growth of fungi, etc. On the flip side, moisture levels below 5% can decrease vigor. Organizations like seed banks and germplasm centers that store seeds long term often will desiccate seeds to around 8% humidity to extend storage, but this isn’t usually needed for home gardeners.

Image result for seed vault
You don’t have to replicate conditions at the Global Seed Vault to have seed saving and starting success

Storage tips
Knowing that we need low temperatures and low relative humidity to extend seed life gives us some clues on how to store seeds to get the longest shelf life. This is key info if we’re trying to start seeds in spring that have been stored, or if we need to store extra or saved seeds. For the needed temperature levels, your standard home refrigerator is acceptable. Storage temps for cold foods are around the 40°F mark. However, humidity in a refrigerator is very variable. Humidity can skyrocket when doors are open, as condensation settles from warm room air settling on surfaces accumulates. Auto defrost cycles can also alter humidity. You’ll want to think about a desiccant like those silica packs to ensure that your seeds don’t get too moist. Store them in a plastic bag with the desiccant, and for added protection I always put mine in a sturdy container like a plastic box (or even a canning jar). Storing seeds in a freezer may help with the humidity issue, as any moisture that enters is frozen. You might also want to think about letting your bag or container warm up to room temperature before opening so that you don’t get condensation on the packets or the seeds themselves.


Vegetable Garden Seed Storage and Germination Requirements – Nebraska Extension

Principles and Practices of Seed Storage – USDA

Seed Storage Guide – Johnny’s Select Seeds

Smith, R. D. (1992) Seed storage, temperature, and relative humidity. Seed Science Research 2, 113-116

120 Year Old Experiment Sprouts New Gardening Knowledge – MSU

Standing up for (and lying down on) the environmentally sustainable lawn

If you’ve been reading this blog for a while, you might remember that I got rid of our lawn (getting rid of your lawn post) at our Seattle house . It took too much water to keep it green in the summer, and the resulting ornamental landscape was more ecologically diverse and aesthetically pleasing for such a small site.

On the way to replacing the lawn with landscape
And the same landscape a few years later.

But that was then, and this is now. In 2017 we moved back to the family farm, which has a full acre of landscape – including lawn. Although we are slowly reducing the vast expanse of lawn, we will keep part of it because (1) we are on well water and there is an irrigation system and (2) because we are allowing the lawn to become a diverse tapestry of different plant species – an ecolawn, if you will.

Farmhouse landscape with an acre of lawn!

When I was growing up, my father fought unsuccessfully to keep the moss and weeds out. I happen to LOVE the moss and the fact that it grows here has nothing to do with poor drainage or anything else. It grows here because the environmental conditions support its growth. I love the spongy feel of the underlying moss, and it reduces the amount of mowing necessary because it’s limited in height. And no fertilizers or pesticides are needed.

Mossy lawns are lovely for walking…and laying down on.

Speaking of mowing…I hate gas powered mowers. They’re smelly and noisy, they contribute to air pollution, and when something goes wrong you have to take it to small engine repair. These excursions are infrequently successful but always expensive. So imagine my delight is discovering newer battery-powered mowers! All you have to do is swap battery packs. They are quieter, there are no emissions, they don’t smell, and they have an electric engine! No small engine repairs, and they are also lighter for this reason.

A newer technology, battery-operated mower with rechargeable battery

I was even more excited to find compatible leaf blowers. We have tons of Oregon white oak leaves, and we blow them into the beds. We do NOT leave them on the lawn, because they interfere with some of our non-grass lawn inhabitants. They are perfect on the beds because their curly, rigid structure prevents compaction and they keep weeds out while allowing water and oxygen to penetrate.

Keep the leaves off the lawn and over the beds.
Our container violets have escaped into the lawn; covering them with leaves could kill them.

Finally, our ecolawn allows me to see and appreciate the reproductive structures of our mycorrhizal fungi. I don’t even pretend to know the species and whether they are edible. I just love the fact that they appear every fall after we’ve stopped mowing.

Some of our lawn mushrooms…
…and some others…
…and others.

Sometimes lawns aren’t appropriate, as we found in Seattle. But sometimes they are – and as long as they are cared for in an environmentally sustainable manner, they shouldn’t have to be something we apologize for.

Fruit Tree Pruning Basics

Last week I helped to train Master Gardeners about pruning fruit trees. January and February are the months that we recommend fruit tree pruning in Southern California.  In colder climates, pruning may not occur until later when freezing temperatures are minimized and there is less chance of damage to new growth. While trees don’t “need” pruning to bear fruit, pruning practices can enhance fruit production, promote earlier fruiting bearing buds, and increase fruit quality if done in an informed way. In many respects, modern fruit trees have been bred for big fruit, and pruning might need to be done to prevent limb breakage, reduce the number of fruit and position it in the tree fore ease of harvest. Misinformed pruning can lead to disease or loss of bearing wood. “Fruit tree” is a broad category, but for this blog, I am referring to deciduous trees (not subtropicals such as citrus, avocado, mango etc.). Two main categories are common: Pome fruits such as apples and pears and Stone fruits such as cherries, plums, apricots, peaches, almonds and pluots.

The first thing to figure out when pruning any tree grown for fruit production is where the fruit will be formed. This requires examining and understanding buds, twigs and the age of growth that is produced. Second we need to understand the tree’s responses to pruning and how that will affect future fruit production. Finally an understanding of negative consequences of pruning is essential.

Peaches produce fruit on last year’s growth

Apples and pears produce fruit on spurs

Why prune you ask if trees will produce without pruning? Pruning shapes a tree, and helps to create fruiting buds that are conveniently placed for harvest-this keeps fruit pickable with less time on ladders. Pruning gives an opportunity to remove fruiting buds thereby invigorating remaining buds and increasing size and quality of the fruit that will form with less fruit thinning later. Pruning also gives an opportunity to remove diseased, damaged, tangled or infested branches.  While various training styles can be used for structural pruning of young fruit trees the open vase or modefied central leader systems are preferred and descriptions of them can be found in extension leaflets.  For my own trees I usually do not prune them the first year after planting in order to encourage a stronger root system.  In the second and third years I pick scaffold branches or train branches on the central leader.

Fruit is produced on various aged twigs or branches depending on tree species. Peaches produce fruit on growth from the previous year or one year old wood. Since peaches grow vigorously fruiting wood ends up on the outside of a tree. Heading back (or heading) cuts (reducing last year’s branches by at least half their length) will remove ½ the fruit and stimulate buds lower in the tree that will make more fruiting wood. For this reason peaches are usually pruned “hard” to stimulate maximum amounts of fresh fruiting wood. Apples, Pears, Plums, Cherries and Apricots produce most of their fruit on small side branches called spurs. Apples and Pears may also produce fruit from the terminal bud.

Young trees often make many long whips and these are usually headed back (heading cuts remove the terminal bud) to stimulate spurs in the following years. Once the overall shape and size of the trees are set, less pruning is required as spurs may produce fruit over decades of time. As trees mature spurs build up so removing densely clustered spurs on mature trees with thinning cuts (removing an entire branch, spur or twig) will increase the size and quality of fruit formed on the remaining spurs.

Pruning is often used on newly planted trees to form the structure of the tree. When forming the branch structure do no indiscriminately head back every branch as this will stop the growth of the branch that is headed. New growth will only resume from buds that are released to grow. Think carefully about what you want to grow and what you want to slow-down in growth. Pruning is always a growth retarding practice. Branches are best spaced up and down and around a central leader. In other training systems for stone fruits one heading cut when the tree is just a whip will create an open vase shape where all the branches arise from a single point on the trunk. While this is considered a branch defect in shade trees, it is a convenient training system for fruit trees if you don’t let the tree get too large and manage the fruit loads that are produced. Trees trained to a modified open center where branches are spaced on a central leader have stronger branch attachments and can bear greater fruit.

This apple is extensively sunburned from over pruning

As trees age and grow they require regular training with heading cuts to shorten vigorous branches of peaches or thinning cuts to remove whips, water sprouts or other unwanted branches.  Be careful not to over-prune especially in summer or sunburn can result.  When fruit sets in the spring or early summer it can be thinned by hand.  This form of pruning will increase size of the remaining fruit and quality.   Summer pruning is sometimes practiced on very vigorous trees to slow their growth and invigorate buds for the following spring.  Prune with care in the summer espeically on green barked trees like apple and pears to avoid sunburn.

Fail to Plan or Plan to Fail? Planning for a year of garden success

It seems like we’re always adhering to one schedule or another these days.  We have devices and planners to keep track of our appointments, our work schedules, kids schedules, and more. Heck, even the antique seed company clock in my office is telling me to order seeds.  It can seem overwhelming, so you might laugh if I tell you that coming up with a schedule, or a plan, for your garden can be beneficial.  It is especially helpful for vegetable gardeners or those who like to any kinds of seeds. 

Developing a yearly plan for the garden can help you keep ahead of the big tasks, help you stay on top of issues like weather, as well as make sure you get seeds started on time and transplanting done when it makes the most sense.  While some of this may be a review for seasoned gardeners, the number of questions and calls we receive at Extension (and the number of oopsies we see) means that the information could be helpful for many. 

Since my background is in vegetable production, I’ll focus there with some bits and pieces added for ornamentals when they fit. 

Do you have garden goals?

Whenever you are planning your annual vegetable garden, or planning on adding any ornamentals to your gardens or landscape, you should ask yourself a few simple questions.  When you’re dreaming of your garden during the winter is a good time to think of these goals.

1. What are my goals for the garden?  Do I have long-term goals?  What short-term goals can you set for this year to build momentum toward your long-term goals?

2. What resources am I willing to invest in the plants I’m ordering (money, time, water, space)?

3. What are the things I most want to grow?

4. What has worked (and what hasn’t) in your garden in the past?

While it may sound funny to say that you are going to set goals for your garden, it really isn’t all that far-fetched.

If you are planning to add ornamental plants to your landscape, you should think about what you want from those plants — are you looking for color or for structure? how about perennials vs. annuals (or biennials)?

When you are planning a vegetable garden, you should ask yourself not only what you want to grow, but how much. Are you just planting for fresh-from-the-garden eating, or do you want to preserve some through canning, freezing or drying? Are you growing just enough potatoes to eat for a month or two after the garden season, or do you need to select a variety that keeps well so you can store it?

Tips for Planning a Successful Garden

After you set your goals and decide what you want to plant, developing a schedule of when to do what is a good idea to stay on top of everything.  I can’t tell you how many years I had been planning on planting this or that, but then forget to buy what I need or start seeds on time.  A plan can help with that, as well as helping you space activities out over time rather than trying to get everything done in a hectic sprint.  This is especially helpful to new gardeners or busy folks who may forget to start or plant certain things at the right time (I wouldn’t be speaking from experience here.  Nope, this gardener has never been guilty of that.  I meant not to plant all of that garlic that I bought last fall.) To borrow the method used in a popular self-help book, you’re “scheduling the big rocks” as one of the habits of highly effective gardeners.

Keep in mind that it can be hard to “garden on a schedule” as weather always plays a factor in what we can and can’t do in the garden.  Given the wide variability in weather over the last few years in many parts of the country, which many scientists attribute to changing weather patterns due to climate change, it can be even more difficult to pin garden tasks to specific dates.  A plan can help you keep track of everything you need to do, but it should be flexible to take weather into account.

Starting Seeds Indoors

Germinating a variety of plants for our 2018 All-America Selections trials

If you’re starting seeds indoors, decide when you’re going to transplant them to the garden.  You can usually find this information on a seed packet, but you can find resources or consult your local cooperative extension office for guidance.  Keep in mind that warm-season plants typically need to be planted after your average last frost date (unless you’re adventurous and don’t mind gambling with a potential loss).  Cool season crops such as Cole crops (broccoli, cauliflower, cabbage, kale, etc.), leafy greens, and bok choi can be planted before the last frost date, but usually after the risk of a hard freeze has diminished.  For a map of the average date for last spring freeze/frost, check out https://www.ncdc.noaa.gov/news/when-expect-your-last-spring-freeze.  Note that these ranges are determined by analyzing the last frost dates over a 30 year period and the actual dates can vary due to weather variations (made even less predictable by climate change).

Choose the timeframe you wish to plant in the garden and count backward to when you need to start plants indoors. Put both the planting dates and the seed starting times on your calendar.   Also keep in mind that this is the earliest that you can plant warm season crops, but you can plant them later if it works better for you.  While we don’t typically share commercial links on this site, the best resource I’ve found for planning your seed starting and transplant dates for both vegetable and common annuals is https://www.johnnyseeds.com/growers-library/seed-planting-schedule-calculator.html

Direct Sowing into the Garden

For some crops like root crops, beans, leafy greens, and even some squash and cucumbers, direct sowing sees into the garden is ideal.  You can add timeframes to your plan based on previous practice, like knowing that you’ll sow carrots toward the end of March or early April, but keeping an eye on the weather can be even more helpful here.  Success here is more about temperature than timing.  Most plants have optimal germination temperatures, so you want to sow outside when the soil temperature (not air temperature) is at or near those levels.  The following resource has germination temperatures for common crops: http://sacmg.ucanr.edu/files/164220.pdf

If you’re lucky, you can search for local web-connected weather stations that have soil temperature probes.  For example, we have one at our office that we share with clients to make gardening decisions (http://mgextensionwx.com/).  If you can’t find one, NOAA has a few in each state for official climate data.  https://www.ncdc.noaa.gov/crn/current-observations.  Putting “check soil temperature” should be on your garden to-do list regularly until the temps get into good gardening range.

Spreading the planting and harvest through the season

If you’re aiming for harvests throughout the growing season, practice relay planting where crops mature in shifts throughout the garden season rather than all at once. If you’re planning on preserving some of your harvest for winter, planning on larger harvests at certain times in the season can get you the amount of produce you need for a big batch at the time that you need it. Some plants are good at producing through the season, but others, like determinate tomatoes and many beans have a one-time flush of production.  Of course, we also have the crops that are once and done, like carrots and radishes, that only have one harvest.  If we space out planting over weeks rather than planting all at once, harvests (or flowers if you’re growing annuals) can be spread out over a longer period of the season rather than everything maturing at once.  There’s generally a several week (to several month) window for planting crops.

For example, tomatoes can be planted as early as the average last frost date, but can be planted for several weeks afterward.  To figure out how late you can plant a crop, look for the first frost date and count backwards using the “days to maturity” information for the crop.  You’ll want to add on a few weeks to a month to account for having a harvest window and slowing growth as temperatures drop.  Keep in mind that many of the cool season crops can last well into the fall and winter, withstanding frosts and even light freezes, so replanting them for a fall harvest is ideal.

Planning out when to plant annuals, perennials, trees, and shrubs can also help make sure you get those plantings off on the right foot and can allow you to prepare in advance.  For example, if I want to add a tree to the landscape, taking the time to research trees and planting techniques, scheduling any prep of the planting area, sourcing the tree, and planting at the right time could all go on your calendar – that way you are prepared and ready to plant at the correct time.

Other garden tasks

While much of the work of a garden plan is front-loaded to the spring, there’s lots of tasks that we should be planning on doing regularly.  Scouting for and controlling insects and diseases, removing spent plants, mulching, compost turning, and more all come to mind.  Putting these on your schedule rather than  doing them when you think of them can really improve your likelihood of getting them done.  Also think about some of those big things you might have identified in the goals you set for the year.  Do you want to build a compost bin or develop new garden beds?  Plant some trees?  Take a soil test?  Putting these on your calendar can not only help you remember them, but plan ahead as well.  What do you need to do before you build that compost bin?  Do you need to buy supplies and tools (and look for bargains if you’re planning ahead)?  By planning when you’re going to accomplish these tasks, you can plan for success throughout the gardening year, improve your successes, and feel a little less hectic when the planting and growing goes full swing. 

Woodpeckers: Friends or Foes?

[This blog post has been provided by Bec Wolfe-Thomas, an administrator for the Garden Professors blog group on Facebook.]

Pileated woodpecker. Photo by Josh Laymon

Woodpeckers (Picidae) frequently get a bad rap from gardeners. It’s often their impression that the birds irreparably damage trees, but this is untrue. Most woodpeckers are insect eaters; they can hear insects under the bark and in the wood of trees. They then target their drilling with uncanny precision to get their meal. This removal of insect pests, such as emerald ash borer, benefits the tree.

Emerald ash borer larva. Photo by Pennsylvania Department of Conservation and Natural Resources.

And what about the feeding holes left in the tree? This is an exciting bit of tree physiology! Trees are able to compartmentalize or isolate the wounds. After the woodpecker has made a hole to retrieve the insects within, the tree starts compartmentalizing the wound. How long it takes for a tree to compartmentalize a wound and close it depends on species and climate factors.

Compartmentalization of decay in trees (CODIT). Photo from Wikimedia.

Below are photos of woodpecker holes in various states of compartmentalization, from freshly drilled to completely compartmentalized and closed holes. Woodpeckers help keep trees healthy by preventing large pest infestations. And while the small feeding holes might be an aesthetic concern to gardeners, they’re only temporary. They will eventually be compartmentalized and closed, and the tree will be healthier in the long run by having fewer pests.

This woodpecker hole is partially compartmentalized; you can see the edges are rounded, no longer rough. Photo by Bec Wolfe-Thomas.
This wound has fully compartmentalized and all that is left is a pucker on the trunk. Photo by Bec Wolfe-Thomas.

[Please note the larger holes excavated for nesting will compartmentalize but will not close over time.]

Flammability of Landscape Plants–Why the lists are BAD!

California had the worst fires in the last two years of its existence as a state. Hundreds of thousands of acres of brush and forest burned. More importantly thousands lost their homes as fires moved across urban/rural interfaces to destroy communities. The entire town of Paradise, California was burned to the ground. Here in Ventura County, the Thomas Fire was the state’s largest fire by the time it was done, and hundreds lost homes. No other time in history have we been so focused on what will burn, why it will burn, and what we can do to have a “firewise” landscape.

In 2017 The Thomas Fire in Ojai, California was the largest brush fire in the history of California fire fighting. It was surpassed the following year by the Camp fire in Northern California.

Fire authorities around the world have advocated creating defensible spaces around homes that are clear of ignitable vegetation. Some authorities have mandated by law that mulch, pine needles and other debris be removed as a fire prevention measure near structures. There is a general recognition that any plant can burn. Even well irrigated plants will rapidly desiccate and become flammable in the face of strong wind and a heavy fuel load that is inflamed nearby.

Flammability of landscape around homes is dependent on several factors. Vegetation placement can obstruct or allow for fire fighters ability to reduce damage to a home. While it is natural to assume that avoiding flammable plants is a part of this process, there is no standard method for testing plant flammability. Many lists of firewise plants have unknown origin or are just guesses. Flammability can be assigned four dimensions: ignitability, sustainability, combustibility and consumability. These factors refer to time till ignition; time a material will burn; rapidity or intensity of burn and quantity of material that will burn. The components of combustion are influenced by moisture content, percentage of carbon, percentage of volatile compounds; surface area to volume ratio and other factors. The varied factors are usually not all studied at the same time and are not all equally important to plant flammability. Thus assessing flammability even within the context of a controlled study will only partially assess a material’s likelihood of burning under various conditions. Hence most of the lists are not that helpful.

While fresh wood chip mulches are consideder by some fire authorities to be a fire hazard, there is little published evidence of this and a single element like mulch can not be tied to flammbability of the landscape.

Behm et. al. showed that variations in flammability between plant species exists, and also that species within the same genus can vary widely in their flammable nature. Thus lists should not assume species in the same genus all have the same flammability. There is some thinking that flammability is an evolutionary trait that some plants exploit to their benefit, i.e. they are made to burn, such as the California Chaparral plant communities. Simply burning fuels in a laboratory setting does not take into account many of the factors associated with fuel burning intensities. Species differences notwithstanding, the amount of dead plant matter (dead twigs and leaves) vs. live matter, the arrangement of leaves, mulch and adjacent species all play a role in the flammability of the landscape itself which cannot be studied in a lab setting. Landscapes are “fuel bed complexes” with multiple elements that are not replicated in studies. For instance, small leaves from some shrubs ignite easily, but when burned as litter, develop low heat release rates because of poor ventilation.

Testing live plant materials alone is misleading because the flammability of an intact shrub is caused by the interaction of live matter with “necromatter”. Dead tissues are thermal catalysts which ignite live material. The ratio of necromatter to live matter influences flammability and is generally not well studied. Fire modelling also has a role in understanding what will burn. Both wind and slope increase the spread rate and the fireline intensity of burnable plants. Fire behavior characteristics on a given plant also are affected by both its physical and chemical characteristic — tissue mineral and water content have impacts on flammability. This bodes poorly for firesafe plant lists because lists do not consider plant physical or chemical attributes and if moisture levels are low it will burn regardless of its structure and geometry or its status on a list. Sometimes though a dense wall of well hydrated vegetation can save homes such as the avocado orchards that held back fire in the Thomas Fire in Montecito, Ca.

While lists don’t satisfy scientific rigor they are great for policy makers and homeowners who want to know what to plant. Unfortunately many lists are just compilations of other lists, none of which were based on research. Sometimes lists confuse one desirable characteristic with another, such as native plant lists that tout drought tolerance. Many drought tolerant plants are not fire resistant especially after a long dry period, indeed they often evolved to burn under such conditions.

For those that live in fire prone areas, fire resistant plant lists will always be an attractive or even required element of landscapes. Lists will not save a structure in the face of high winds and adequate fuel or embers. A defined defensible space around buildings, and maintenance of plantings that removes dead matter, maintains irrigation, and maintains proper distance from combustible surfaces will be more effective than choosing landscape plants from flammability lists.

Fernandes, P.M. and M. G. Cruz. 2012. Plant flammability experiments offer limited insight into vegetation—fire dynamic interactions. New Phytologist 194: 606-609

Behm, A.L., M. L. Duryea, A.J. Long, and W.C. Zipperer. 2004. Flammability of native understory species in pine flatwood and hardwood hammock ecosystems and implications for the wildland –urban interface. International J. of Wildland fire 13: 355-365.

White, R.H. and W.C. Zipperer. 2010. Testing and classification of individual plants for fire behavior: plant selection for the wildland-urban interface. International J. of Wildland Fire 19:213-227.

A Cactus by Any Other Name: A Case of Mistaken Holiday Cactus Identity

Believe it or not, a cactus, of all things, is one of those plants that have come to represent the holidays and feature in the regular rotation of holiday houseplants. Then again, maybe it isn’t so strange amongst its peers that feature a flashy bulb-grown plant named for a horse’s head (the Latin name of amaryllis is Hippeastrum, literally meaning horse flower), a plant that has ugly flowers but brightly colored leaf bracts and leaks sticky and irritating latex when damaged, or some daffodil-like flowers that have musky odor so strong it makes some people nauseous.  But…..I digress. 

Back to the cactus.  However you see it though, the cacti that make their debut at the holidays are suffering under a case of mistaken identity.  What you typically buy as a Christmas cactus is not a Christmas cactus at all. It is actually a Thanksgiving cactus.  Now this wouldn’t be such a big deal, except that there is such a thing as a “Christmas cactus” — but you won’t find one on store shelves. Nay, it is hard to even find one in garden catalogs.  And this is sad, because the Christmas cactus is, I think, even more beautiful than the Thanksgiving cactus. 

How did we end up ignoring the beautiful Christmas cactus in favor of its holiday cousin?  It all comes down to timing and how we buy things for the holidays.  It seems that, as the shopping and holiday seasons creep ever upward on the calendar, retailers have little love for a cactus that is actually programmed to bloom at Christmas. They need something that blooms earlier so that it can be on the store shelves as early as possible. (At this pace, breeders will need to develop and Independence Day cactus for the Christmas shopping season.)

Therefore, the Thanksgiving cactus has been rebranded as a impostor stand-in for the true Christmas cactus. We won’t even talk about the Easter cactus, which just totally feels left out of the family (and yes, there is such a thing and it is beautiful).

These cacti were in cultivation in Europe by 1818 and various different species were being hybridized, probably most notably by W. Buckley.  The most notable hybrid, bred now named Schlumbergera ‘Buckleyi’ is considered to be the first actual “Christmas cactus” and associated S. x buckleyi hybrids are still grown as Christmas cacti.  Cultivars and crosses of S. truncata are the Thanksgiving cacti that have been rebranded as Christmas cacti.  They can be identified by their flattened stems (or cladodes or cladophylls) that have spiky, toothed edges and zygomorphic (now that’s a fancy word — it means that they have a two-sided, or bilateral, symmetry) flowers.  Most of the Thanksgiving cacti that have these characteristics.

W. Fitch (drew), Swan (engraved) – Bot. Mag. 66. 3717, as Epiphyllum russellianum Source: Wikimedia commons

You’ll most commonly find them in pink colors, but you can now find them in yellowish colors. The flower shape often leads to its nickname: “Zygo cactus.”

S. x buckleyi are the true Christmas cacti and form what is called the Buckleyi group.  Most of these have characteristics that come from the species S. russelliana, which was used in the early Buckley crosses. They can be identified by their rounded, less pointy cladodes and round, radially symmetrical flowers. They do have a similar growing form, but those in the know can tell the difference.

And for those following along at home, the Easter (or spring) cactus used to be considered part of the Schlumbergera genus (S. gaertneri) and then the Rhipsalidopsis genus, but now is classified as Hatiora gaertneri has radially symmetrical flowers but the cladodes are three dimensional rather than flat, elongated, and scalloped.  They have a wide range of colors, such as red, pink, and even orange.

Holiday cactus care

It’s a cactus, so it should be easy to care for – I just water it sparingly and keep it dry, right?  WRONG!

Whether you have a Thanksgiving or Christmas cactus (or an Easter one, for that matter), you take care of them the same way. Keys to their care come from their native habitat, which is not a desert but the cloud forests of costal south-east Brazil.  The high-altitude costal areas where they’re from are cool, shaded, and relatively humid with the mists and moisture rich air. They are epiphytic or lithophytic – meaning that they grow on trees and in crevices with decaying plant material rather than in the soil.  And while you don’t need to know this to grow them, the morphology of the flowers have developed to support the feeding of hummingbirds which act as their main pollinator.

Since we don’t grow them epiphytically, when we pot them we need to make sure that we provide a light substrate for them to grow and to get plenty of oxygen to the roots. Potting mixes should have a high ratio of peat or coir and even some bark or other coarse woody material.  As for watering, you’ll want to keep the soil fairly moist, rather than dry.  You’ll also want to let them dry slightly between watering, but don’t think that they like to live the life of dehydration — you do need to keep them watered.

One of the reasons that they bloom at very specific time of year has to do with light and, to a lesser extent, temperature.  They are short-day (or rather  long-night) plants, so they flower as days grow shorter (or longer, in the case of the Easter cactus) and nights grow longer.  The Thanksgiving cactus will bloom with just a little shorter dark period than the Christmas cactus, which is why it blooms in late fall as opposed to the Christmas cactus that blooms closer to when days are the shortest around the solstice.  They will also bloom better and longer if they have cooler temperatures, so keeping them in a cool area of the house is ideal.  In high light situations the cladodes will turn red.  Keeping them too dark, however, will limit growth and keep them from thriving.

Since they are short-day plants, the plants need a period of several weeks where the period of darkness at night is 12 hours or longer for their flowers to begin forming.  This occurs naturally about mid-October, but you can delay flowering by using grow lights to lengthen the day (or keep in mind that bright indoor lights can also limit or reduce blooming).  Also, don’t be alarmed if they bloom at odd times through the year.  Since daylight coming into your windows can be altered by window treatments or films, the light levels can technically be “just right” for flowering at multiple times per year.  In my old office the tint on the windows created the right conditions at least once or twice per year – one year I had a Halloween cactus and the next it was a Memorial Day cactus. 

If your cactus does not flower, you need to move it to a spot where it gets at least 12 hours of relative darkness to initiate blooms (keep away from indoor light sources or windows near outdoor lights). Hopefully, you’ll have lots of colorful blooms for Christmas…..or whichever holiday your cactus celebrates. 


Is it a Thanksgiving, Christmas, or Easter Cactus? https://www.extension.iastate.edu/linn/news/it-thanksgiving-christmas-or-easter-cactus

McMillan, A. J. S.; Horobin, J. F. (1995), Christmas Cacti: The Genus Schlumbergera and Its Hybrids (p/b ed.), Sherbourne, Dorset, UK: David Hunt

Soil or dirt? It’s really up to you

Dig up dirt. Treat like dirt. Dirt poor. Replace the word “dirt” with “soil” and you get phrases that make no sense. This is a roundabout way of explaining that “dirt” and “soil” are not the same things, either in idioms or in the garden. Yet many of us effectively turn our soils into dirt through poor garden practices.

This is dirt. (Photo from Wikipedia)

This is soil.

For the purposes of this post, we’re going to use a single criterion to distinguish between soil and dirt: one is a living ecosystem and the other is not. A thriving soil ecosystem contains sufficient water, oxygen, and nutrients to support bacterial, fungal, plant, and animal life. Regardless of soil type, about half of the volume in a living soil should be pore space and the other half soil particles. Half of the pore space should be filled with water and the other half with air. When we make choices about activities that affect garden and landscape soils, we need to be proactive in preserving both the particle-pore balance as well as connectivity between the soil and the atmosphere.

All soils have pore spaces regardless of their texture.

Pore size varies with particle size.

The only way pore space can be reduced is through soil compaction. So don’t do it.

  • No driving. If equipment must be brought in, put down a thick layer of wood chips to protect the soil, or at least plywood.

Not really the way to do park renovations.

These amenity trees quickly became liabilities, thanks to soil compaction during construction. {Photo courtesy of Jim Flott)

  • No naked soil. Bare soils are compacted soils. Mulch!

Basically dirt.

Wood chips covering real soil.

  • No rototilling. It grinds your living soil into dirt. Disrupt the soil as little as possible when you plant.

I have no words.

  • No stomping, pressing, or otherwise compacting the soil during planting. Let water and gravity do that work for you.

Let’s just press that pore space out of existence.

Mud it in! Let water and gravity settle new transplants.

The only way soil and atmosphere connectivity can be disrupted is by covering the soil with low permeability materials. So don’t do it.

  • No soil layering. Don’t create abrupt layers of soils with different textures. It interferes with water and gas exchange.

Soil horizons change gradually in natural soils.

Poor surface drainage indicates a perched water table caused by abrupt changes in soil texture (photo courtesy of Rich Guggenheim).

  • No sheet mulches. I’m sure you’re tired of hearing me say that and I am tired of saying it. Sheet mulches have less permeability than chunky mulches. That means oxygen and water have more difficulty getting through. Period.

The less porous the material, the more slowly gas diffuses through it. Read more about it in our recent article

Chips are great. Why ruin them with cardboard underneath?

Landscape fabric is even worse than cardboard, but the weeds love it.

And plastic? Dont even THINK about it.

Do use lots of groundcovers, chunky mulches, and hardscape in areas where there’s considerable foot traffic. They all protect the soil and are important parts of a well-designed, sustainable landscape.

Soils love all sorts of mulches.

Inorganic mulches protect soil, too.

If you just can’t get enough about soil science for gardens and landscapes, do check out this new publication by Dr. Jim Downer and myself.

Fertilizer—Friend or Foe to disease causing organisms?

Gardeners that read this blog understand that minerals are absorbed mostly by plant roots as ions, and are essential for plant growth and development. Some minerals are required in parts per hundred, and are macro-nutrients while others are only required in parts per million or parts per billion, and are considered micronutrients. As long as enough of the 16 most essential minerals are available, plants grow and reproduce in a healthful way. When not enough of one of the essential elements are available, a deficiency occurs, and plants

Nutrient deficiency symptoms in new growth of Camphor tree

may present deficiency symptoms. Mineral nutrient deficiency symptoms are considered abiotic disorders. There are, however, cases where excess or deficiency of elements can be predisposing to disease caused by pathogens. Most some mineral elements do have a role in the development of disease caused by some pathogens but this is largely demonstrated in agriculture and often most home gardens do not suffer nutrient caused plant diseases.
Diseases can be either biotic with a living pathogen driving the disease or abiotic where a physiological condition is caused by the environment and host interactions. Mineral nutrients also are often implicated in abiotic disease.


Blossom end rot in tomato fruit

Perhaps the most famous one is blossom end rot of tomato. This disorder is seen by gardeners around the country and is widely attributed to calcium deficiency. Expanding fruit are a tremendous “sink” for nutrients like calcium and it was thought that if not enough calcium was available in soil the disorder would occur. It is accepted that localized Ca deficiency (in fruit) may play a role in the initiation of blossom end rot, but there are many other factors that lead to the full blown condition, some of which are not fully understood. The fact that blossom end rot (BER) occurs in calcic soils in California underpins the complexity of this disorder.  In many cases, simply adding calcium to soils does not correct the problem. Research in California suggest that the plant hormone abscisic acid (ABA) regulates water flow, the development of water conducting tissues, and calcium uptake in tomato. Researchers found that ABA treated tomatoes were cured of blossom end rot.  For gardeners, making sure plants are fertilized, and avoiding varieties susceptible to BER is the best course of action.

Soil-borne pathogens are perhaps most affected by minerals dissolved in soil solution. Minerals can act in specific ways (specific ion effects) or as total ion effects (osmotic strength or concentration) having direct impact on pathogenic propagules or on the host itself. In a biological disease relationship there are several possibilities:
• Specific ions harm or favor the pathogen.
• Specific ions harm or support the host.
• Ionic strength changes the root environment making the host weak and susceptible.
• Ions change the pH of the soil solution making it more or less fit for a pathogen or the host.
• Ions change the soil physical environment making it more or less fit for a pathogen or the host.

Root rot of annual color plant is a common find in many garden centers

While it is often espoused that the well “fed” or fertilized plant is resistant to disease, it is rarely borne out in published research on ornamental plants. Keeping a good nutritional level in nursery stock will not necessarily protect plants from many of the virulent pathogens that are capable of causing disease. Excess fertilization may lead to luxury consumption by the fertilized plant and can produce succulent growth that will exacerbate of such diseases as powdery mildew. It is well known that seedling diseases caused (damping off) are more severe with increased medium salinity and it was later discovered that increased soil salinity also increases susceptibility of ornamental plants to Phytophthora root rot diseases. Phytophthora is the most common pathogen associated with rotted roots in most gardens.

Plant mineral nutrition supports plant health in two basic ways (1) formation of mechanical barriers (cell wall strengthening) and (2) synthesis of defense compounds that protect against pathogens. The role of specific elements and their compounds is complicated and unique to each disease/host system. Certainly deficiencies of molecules such as calcium and potassium can interrupt either defense mechanism and if nutrients are supplied enough to prevent deficiencies there is little role of nutrients in preventing disease.
Root rot is a disease of thousands of ornamental plants and a serious problem in many gardens. Root rots caused by Phytophthora spp. occur in a range of nutritional and pH ranges. Nitrogen has been shown to lessen root rots and this is likely due to conversion of nitrogen into ammonia gas in soil which acts as a fumigant. Many studies found no relationship of nitrogen source to root rot disease development.  Calcium increases disease resistance to root rot in avocado and other plants. While it is understood that calcium has direct effects on plant membranes, root cell membrane leakage, cell wall thickness, and many other host factors, there are also direct effects on the pathogen in soil. Calcium ions reduce the production of disease spores and disrupt their ability to swim and find susceptible roots. When soils and soil less media are low in soluble calcium, when calcium is easily precipitated out of solution, or when the pH is high and limestone minerals decrease the availability of calcium, root rots will be able to infect.  Increases of sodium ions in soils and soil less media can also increase Phytophthora caused diseases.

Some non-essential elements have become popular as disease suppressants. Research has shown Silicon increases resistance of plants to powdery mildew, root rots and to stress in general. Silicon is implicated in strengthening cell walls as well as in defense protein production in plants. But not all plants are capable of utilizing silicon, so its role in plant defense is limited to those species (mostly grasses) capable of metabolizing it. Silicon has been erroneously recommended for widespread disease prevention. Its actual utility is likely very narrow. Much more study is necessary to understand silicon’s role with ornamental plant-pathogen systems. Gardeners will find little use for silicon as a disease prevention too.

Plants extract minerals from container media and garden soils—the process is complicated; it is mediated by the substrate/soil, water chemistry, temperature and the applied minerals (fertilizers) as well as by plants. Gardeners should apply fertilizers that can supply a constant low level nutrient charge or rely on nutrients provided in mulches. Fertilizing decisions are best guided by having a low cost soil analysis by a University lab. Supplying extra soluble calcium may be helpful in managing root rots, especially where heavy rainfall is normal and soils may be highly leached. Preventing salt build up (by leaching irrigation) in high salinity soils (low rainfall places) and that can occur when media dries out, will also help plants avoid infection by root rot organisms. It is good to remember that fertilizers never cure diseases, but there may be a role in preventing disease when plants are nutrient deficient.
Baker K.F. 1957.  The UC System Producing Healthy Container-Grown Plants. University of California Division of Agricultural Sciences Agricultural Experiment Station Publication #23.

Cherif M., Asselin A., Belanger R.R. 1994. Defense responses induced by soluble silicon in cucumber roots infected by Pythium spp. Phytopathology 84:236-242.

Datnoff, L.E., Elmer, W.H. and D. M. Huber eds. 2007. Mineral nutrition and plant disease. APS Press The American Phytopathological Society, St. Paul, MN. 278pp.

Downer A.J., Hodel D.R., Matthews D.M., Pittenger D.R. 2013. Effect of fertilizer nitrogen source on susceptibility of five species of field grown palms to Fusarium oxysporum f. sp. canariensis. Palms 57: 89-92.

Duvenhage J.A., Kotze J.M. 1991. The influence of calcium on saprophytic growth and pathogenicity of Phytopthora cinnamomi and on resistance of avocado to root rot. South African Avocado Growers Yearbook 14:13-14.

Faufeux F., Remus-Borei W., Menzies J.G., Belanger R.R. 2006. Silicon and plant disease resistance against pathogenic fungi. FEMS Microbiology Letters 249:1-6.

Kauss H., Seehaus K., Franke R., Gilbert S., Dietrich R.A., Kroger N.. 2003. Silica deposition by a strongly cationic proline-rich protein from systemically resistant cucumber plants. Plant J. 33:87-95.

Lee B.S., Zentmeyer GA. 1982. Influence of calcium nitrate and ammonium sulfate on Phytophthora root rot of Persea indica. Phytopathology 72:1558-1564.

Ma, J.F.  2011. Role of silicon in enhancing the resistance of plants to biotic and abiotic stresses. Soil Science and Plant Nutrition 50:11-18.

Macdonald J.D., Swiecki T.J., Blaker N.S., Shapiro J.D. 1984. Effects of salinity stress on the development of Phytophthora root rots. Cal Ag 38:23-24.

Messenger B.J., Menge J.A., Pond E. 2000. Effects of gypsum on zoospores and sporangia of Phytopthora cinnamomi. Plant Dis 84:617-621.

Powell C.W., Lindquist R.K. 1997. Ball Pest and Disease Manual (2nd ed). Ball Publishing Batavia Publishing. 426 pp.

Span T.M., Schumann A.W.  2010.  Mineral nutrition contributes to plant disease and pest resistance. University of Florida Publication #HS1181. http://edis.ifas.ufl.edu.

Tonetto de Freitas, S., K.A. Shackel and E. J. Mitcham. 2011. Abscisic acid triggers whole-plant and fruit specific mechanisms to increase fruit calcium uptake and prevent blossom end rot development in tomato fruit. J. of Experimental Botany 62:2645-2656.

Daylor, M.D. and S. J. Locassio. 2004. Blossom-end rot: A calcium deficiency. J. of plant Nutrition 27: 123-139.

Zentmeyer G.A. 1963. Biological control of Phytophthora root rot of avocado with alfalfa meal. Phytopathology 53:1383-1387.