[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.
Freshly drilled holes. Photos by Bec Wolfe-Thomas.
This woodpecker hole is partially compartmentalized; you can see the edges are rounded, no longer rough. Photo by Bec Wolfe-Thomas.
These wounds are almost completely compartmentalized with very little gap between the edges. Photos 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.]
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.
References:
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.
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.
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.
Schlumbergera x buckleyi Christmas cactus
Schlumbergera truncata Thanksgiving cactus
Hatiora gaetneri Easter cactus
My holiday cactus collection
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.
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.
