The Garden Professors™

Terrariums are are contained environments that allow culture of plants. They take many sizes, shapes and dimensions and can be sealed or open. At the least terrariums are just plants in a bottle, in their highest form they are cultivated landscapes in miniature. Closed terraria create a unique environment and opportunity for plant growth. The transparent walls of the container allow for both heat and light to enter the terrarium while maintaining high relative humidity and preventing system water loss. Sealed containers combine retained moisture and heat which allows for the creation of a small scale water cycle. This happens because moisture from both the soil and plants evaporates in the elevated temperatures inside the terrarium. Water vapor then condenses on the container walls and eventually drips back onto plants and soil below. A sealed terrarium is ideal for growing some kinds of plants due to the constant supply of water, thereby preventing them from becoming dry. Lowland jungle plants from warm climates will do well. Some cloud forest plants, orchids and bromeliads will not fare well in sealed environments because they require more air movement and/or cooler temperatures. Terrarium culture can allow growth of plants difficult to cultivate even in greenhouses. Terrariums can be displayed to great effect and are an easy method of indoor gardening. Success with a terrarium garden requires an understanding of the container, light, media, and the plants themselves.

A Word about the Plants
A contained environment is not for all plants. When in a sealed environment, certain plants such as cacti or succulents will grow poorly or in a manner not suited to their habit (lanky or etiolated growth). Problems arise when plants not suited to a small contained environment are used. Plants such as Syngonium, Diffenbachia, and the larger Peperomia spp. look good when planted initially, but will soon outgrow their space–they are not suitable for closed terrariums. The classical “florist” terrarium planted with very young houseplants looks good at first but is completely unsustainable for months or years. A well designed terrarium should grow for multiple years before a complete tear down and replant is necessary. Thus it is necessary to select truly miniature and high-humidity-loving plants for closed terrarium culture. Ferns, sellaginellas, gesneriads, begonias and some peperomias are suited for these conditions. Obtaining truly miniature and humidity loving plants is difficult. Online vendors are the most accessible sources, but also other hobbyists or plant societies can be sources at their annual sales. Nurseries carry some of these plants but the vast array and diversity of rare plants are found on Ebay and Etsy. Many nurseries list plants under the ‘terrarium plants’ search words that are not really suitable, so take care to look for truly small or miniature plants. Perhaps start with the list I have provided at the end of this article for some of the tried and true plants that will work well. Terrarium gardens are not sustainable if you make bad plant choices, you will eventually end up removing plants that outgrow their containers.

The Container
Once you have your plants, you are ready to start. Or you can start before getting your plants and set up your terrarium now to plant later, or in stages, as you acquire new specimens to add into your contained garden. The first consideration is a suitable container. The larger the container the easier it will be to plant, grow and maintain your garden. Larger containers will also allow for a greater diversity of plant types. Fish aquariums may not be the most attractive, but are the most practical in many ways. Because they are rectangular they allow for placement of a light on the lid and they are easy to cover and place on square surfaces such as tables or window sills. Glass containers are preferred over plastic because they maintain transparency better over time. While bottles are attractive, if you can not get your hand inside they can be very difficult to plant and maintain.

The Media
Lowland, humid jungle plants grow in decomposing organic matter. For our purposes peatmoss is the best medium. It can be amended with fine horticultural perlite (20-30%) or sand. Sand will make a heavier mix, and, if you are doing a large terrarium, mix weight is important. If not, sand is ideal. Also, since terrariums are contained, they may become disease gardens if you are not careful. Therefore I recommend sanitizing your media in a microwave until the media temperature exceeds 160F. Keep the bag closed until the media cools. A turkey roasting or other microwave safe bag works well. Media can be sanitized in a conventional oven–it just takes longer. Media should be moist but not wet when microwaved. Distilled water can be added later to moisten the media after planting. Commercial mixes can be used for terrarium media but care should be taken. Search the blog for my article on potting soils.

Since terraria are sealed environments, you need a reservoir for the water and a filter. Create the reservoir with coarse horticultural perlite (#3) up to an inch thick (the bottom most layer) depending on size of the container –the bigger container, the thicker the layer. Cover the perlite with activated charcoal. Fish aquarium charcoal or horticultural charcoal from the nursery is fine, but NOT charcoal briquettes. The charcoal layer just covers the perlite. Now add soil. Slope the soil from thin in the front to thicker in the back. You can also add wood, sticks, and rocks to make interesting landscapes. They should all be sanitized in the dishwasher or boiled or microwaved until sterile. After placement of soil, rocks and sticks are ready to plant. Place larger growing plants in the center and rear and small vines up front.
Your container should be sealed either with “cling tight” plastic wrap or glass. I prefer glass for most applications.

Light
While terraria can grow in window light, especially north light, it is not optimal for most plants and they will grow slowly. You can’t place terraria in direct sunlight or the plants will “cook” because closed terraria can’t dissipate heat that rapidly. The old standard for light sources is fluorescent tube fixtures, but they have been supplanted by Light Emitting Diode (LED) technology. Grow-light LED fixtures are expensive, but provide some performance differences. Terrariums are not crops and we don’t want them to grow too fast so find an affordable light source that works for you. LED sources are nice because they are not bulky and do not add large amounts of heat. A bit less light or less optimal wavelengths of light are ok because we want to sustain plant growth for a long time, not grow the plants to the edge of the container real fast and have to prune or start over. The Costco brand shoplight LED fixture is perfect, but it is four feet long. Smaller LED fixtures would be appropriate for smaller containers. The Costco fixture is perfect for a 60 gallon fish tank. White light works well and looks best. Red and blue LED fixtures change the way we see the plants and are not best for viewing. Light should come from above so plants will appear to be growing normally. If the terrarium is placed near a window it will need to be rotated to keep plant growth even.

Moisture
Moisture is critical in terraria. The growing medium should hold a shape when squeezed but not be saturated when you plant. After the terrarium is planted, you can “water it in” with a dilute -1/4-strength fertilizer solution mixed into distilled water. Watering amounts will vary by container size. Water should penetrate soil to the depth of roots and some should enter the reservoir. No more watering is necessary again until some time later when plants have grown considerably—usually months later. I usually water the glass to clean it from the initial planting with a turkey baster. At some point in the future, months not weeks, the soil may dry as growing plants use up water. When this occurs, water again with another dilute fertilizer solution. Do not over water your terrarium or bad things will happen. Also resist misting or spritzing as this will cause leaves to rot and is not necessary in a sealed environment.

Pruning, Replanting and Maintenance
Some of your chosen plants may outgrow their space. Some like Ficus minima ‘quercifolia’ will just overgrow everything, the same can happen with common Sellaginella sold in nurseries such as S. brownii. You should plan on pruning back the plants and making cuttings or planting other terrariums with the prunings. Cut begonias below a node or along the rhizome. Rhizomatous ferns can be clipped or dug and planted elsewhere. If you have to remove a really big plant it will leave a hole. New sterilized mix should be added to fill the hole along with the new plant occupant. Removal of flowers, mushrooms (should they form) and dying leaves is important. They will cause rots on plants they fall on. Sticks are usually always a problem since it is very difficult to kill mushroom fungi living in them. Mushrooms are mostly non-toxic to plants, but they drop spores and these lead to rot on sensitive begonias and ferns. Clip back Begonia, Episcia Sellaginella, Peperomia or Ficus to prevent them from overgrowing other plants.

Recommended Plant List
If you can find them, here are some recommended plants for terrariums.
Begonias
B. prismatocarpa
B. prismataocarpa variegata
B. versacolor
B. ‘Raja’
B. ficicola
B. exotica
Ferns
Edanoya spp.
Humata parvula
Lemmaphyllum microphyllum
Microgramma spp.
Pecluma pectinata
Tectaria spp.
Quercifelix zelanica
Others
Peperomia prostrata
Sininngia pusila and all its variants
Episcia spp. (there are many, I like the pink ones)
Saintpaulia (african violets-only miniatures)
Sellaginella erythropus
Sellaginella spp. (there are many kinds, S. brownii is most common)
Ficus minima ‘quercifolia’

It’s not my week to post on the blog, but this is a PSA for California residents. Having visited the Capitol grounds in Sacramento, I find it important to make others aware of the plans to remove a number of large and historically important trees for the purpose of building a parking garage and expanding the Capitol building space.

I’m not a California resident, so in a sense it’s none of my business. But I am an urban horticulturist, and an arborist, and committed to preserving trees especially in urban environments. These trees are irreplaceable unless you want to wait a few hundred years. The plans to “relocate” some of these large trees are probably not realistic given the size of the specimens.

More importantly, this is public space and the public should be actively involved in discussions. But the process has been secretive and under the radar of a public more concerned, and rightly so, about COVID-19 and all the associated fallout from the pandemic. But it’s not too late.

Please share this post with California residents who have should have a say in how their land should be managed.

For those Californians interested in supporting the effort to save the trees at Capitol Park and call for the development of a Park and Tree Management Plan, you can sign the petition at https://www.change.org/p/california-state-legislature-save-california-state-capitol-park.

More importantly, you should call AND write to your own California legistator at this website findyourrep.legislature.ca.gov, as well as the two Legislative leaders who can really pause the project and guide its re-planning:
Senator Toni Atkins, President pro-Tempore of the Senate, 916 651 4039 and senator.atkins@senate.ca.gov. UPDATE: This email does not appear to work. Try using this form.
Assembly Member Anthony Rendon, Speaker of the Assembly, 916 319 2063 and speaker.rendon@assembly.ca.gov

Summer is a time of bounty in the home garden. During June, July and August the majority of small fruits ripen on home orchard trees. Plant health care is important to consider in advance of summer bounty. Careful dormant season pruning, dormant sprays, mulching and care helped to produce a nice harvest. As the fruit comes off the tree, some summertime options are available. This is a time when some limited summer pruning can be done to manage the physiology and growth of many fruit trees. Even some citrus will benefit from careful summer pruning.

One obvious reason to prune in summer is to repair broken and remove dead branches that may have occurred from excess fruit weight or other injuries. Breakage is common in peach, plum and apples if fruit loads are not thinned earlier in the season. Cut the broken branch from the stem it attaches to with an angled cut that leaves the branch collar intact. Do not cut branches flush with the stem they were attached to. Many years ago the myth of flush cuts for shade trees was found to permanently damage trees, but flush cuts are often still practiced on fruit bearing trees. Flush cuts allow decay organisms to enter trees leading to heart rot and other kinds of wood decay.

Another myth that persists in home fruit orchards is painting wounds with a ‘sealant’ or ‘protestant’. There is no reason to paint cuts. They do not limit the progress of decay or prevent decay from forming behind the paint. Pruning paints do not promote “healing” or callus formation to close the wound. There is some thinking that pruning paints may even accelerate the process of decay formation. So throw away the black tar, it has no practical purpose in support of pruning.

While pruning paints are no longer used, paint has other functions that can be helpful. If a large branch was removed from a tree, sometimes the remaining branches may require protection from sunlight. Apples and other thin-barked trees (citrus, cherries, etc.) are very susceptible to sunburn. If branches that were previously shaded are suddenly exposed to high light levels, the bark can be destroyed leading to sunburn cankers and entry of disease-causing fungi such as Botryosphaeria spp. If repair pruning exposes a large gap in the canopy, it is appropriate to apply white wash or diluted white latex paint to exposed branches in order to protect them from bright sunlight. The most severe damage occurs on southern and west facing branches. Sunburn is one of the leading causes of abiotic damage and a predisposing factor for disease such as stem and branch cankers in apples.

Fireblight is another common disease on pears and apples and develops after bloom. Pruning out fireblight affected twigs helps to arrest disease progress. Finally, bacterial canker can be devastating to Prunus (plum, cherry, peach, nectarine and almond) in parts of the country with warm summer rains. Immediate removal of bacterial canker affected branches is necessary to prevent permanent damage to the tree. Tools used to remove cankered branches should be sanitized by flame (torch) or with disinfectants. Canker diseases are active in the warm summer growing season. Cankers can be caused by bacteria or fungi and should be dealt with as soon as symptoms are noticed. The earliest symptom of an active canker is slowed growth relative to other branches on the tree. Slowed growth results in smaller leaves and fruit and fewer leaves. Affected branches seem more open and just look “weaker” than their healthy counterparts. Slowed growth is often followed by wilt, leaf drop and eventually necrosis or death of the branch. It is best to remove diseased branches early before the organism spreads to the main stem. Since symptoms occur when leaves are on, summer pruning is the best approach to remove cankered branches. Regardless of where or when damage occurs, using correct pruning practices should be adhered to.

Healthy growth on the tree above but thin, weak, small leaves on the tree below indicate a developing branch canker.

Pruning is used most widely on fruit trees to dwarf them so that fruit is produced at a height convenient for harvesting. Pruning creates two universal responses that apply to all woody plants:

I. Pruning is growth retarding. The part of a tree pruned will grow less than the unpruned part. Or, a pruned tree will grow less than an unpruned tree.

II. Pruning is a bud invigorating process. A pruned tree or branch will have more of its buds released to grow compared to the unpruned branch or tree where many buds remain in a dormant state.

The more a tree is pruned, the less its roots and stems will grow. Even though the more a tree is pruned the more latent or axillary buds will be released to grow, it will not be able to make up for the lost leaf potential of the unpruned tree. The pruned tree has reduced photosynthetic capacity, makes less energy and will grow less overall. The thing that is not very clear is how the timing of pruning affects the basic processes. In his review, Chandler makes clear that pruning in the dormant season will retard the growth of apples less than if they are pruned in the summer. Summer pruning also significantly reduces the growth of roots compared to dormant season pruning. Removing leaves in mid-summer or after all shoot growth has stopped (summer rest period), removes photosynthetic capacity and reduces stored energy in the tree, thus retarding growth overall. While buds may be invigorated and new summer growth may occur, this rarely makes up for the tissue lost and still results in growth reduction.

Summer pruning does not result in more fruitfulness the following year, and in apples does not increase the number of spurs formed for fruit formation. Summer pruning can open the canopy and allow branches to form lower down that are useful for easy harvest. The effect of summer pruning on next year’s fruit quality is uncertain. Summer pruning can accelerate the ultimate scaffolding or canopy shape for the mature tree.

Pruning citrus after harvest, during the warm season can affect fruit size in the following year. This may be due to fruit thinning as some citrus have green fruit formed by summer that ripen in winter or spring. Summer pruning removes fruit and remaining fruit can grow larger.

Summer pruning of fruit trees before fruit harvest increases light penetration into the tree and can increase color development of the fruit. Pruning must be done cautiously to avoid excess light penetration and sunburn to scaffold branches and resultant canker diseases. Summer reduction pruning is most often accomplished by pruning the ends of branches back to other branches or twigs. Removing about one half the current season’s wood (on a given branch) will achieve objectives usually without causing excessive light penetration into the canopy. Not every branch need be pruned but an even approach, removing branches consistently around the tree, will maintain form. No more than 15-20% of the canopy should be removed by summer pruning. On some vigorous growing trees such as Persian mulberry, pomegranate, or some peaches, heavier pruning doses can be used. Pears, apples, plums and cherries require less pruning and cuts should be made to preserve spurs and other fruit bearing wood. Some varieties of cherries can become ‘over spurred’ and thinning cuts to remove excess spur wood can sometimes be helpful to limit production and increase fruit quality in the next season.

References:

Chandler, W. H. 1923. Results of some experiments in pruning fruit trees. Cornell University Agriculture Experiment Station bulletin 415.

Ingels, C. and P. Geisel. 2014. Fruit and Nut Tree Pruning Guidelines for Arborists. University of California Agriculture and Natural Resources publication 8502. http://anrcatalog.ucanr.edu

Saure, M.C. 1987. Summer pruning effect in apple—a review. Scientia Horticulture 30: 253-282

I have been hiding from COVID-19 in Arizona, but I had to return to Ojai, Ca because I was “noticed” by the local fire department to abate my weeds. I returned to find the Weed Apocalypse (WA 2020). Late spring rains were spaced nicely in California supporting rampant weed growth. So, why did this happen? What can I do about it now? How could I have better prepared for WA 2021 next year?

In May, the days are getting noticeably longer and moving closer to the longest day of the year (June 20–the summer Solstice). Longer days add more photosynthetically active radiation and put plants on a rapid growing phase at this time of the year. If water and soil nutrients are not limiting, this is the fastest growth period for most plants. Weeds have the unique quality that they will grow faster than many garden plants even with less resources. When resources are plentiful, they grow  faster still.

One way to prevent the weed apocalypse is to deteriorate the weed seed bank . The “weed seed bank” (WSB) is the amount of seeds stored in soil that are viable. The seed bank is restored each year when weeds set seed and drop them on or into the ground. In some cases the seed bank also includes plant parts such as Bermudagrass (Cynodon dactylon) stems and rhizomes (underground stems) that can lie quiet but, once sufficient moisture is available, they spring into life! So once the weeds set seed, just “whacking” or mowing and leaving the mulch behind does not usually solve the problem as viable seed is added to the WSB. Annual weeds can be reduced substantially if they are controlled prior to seed set.

Weeds are sneaky buggers. They imbue their progeny with germination inhibitors or dormancy factors that delay germination. Some seeds complete their maturation even when they have been cut away from the main plant. This is why weeds always seem to be there for you. When dormancy factors wear off, or are washed away seeds will germinate. So after a strong rain event or irrigation weeds emerge that were previously dormant. Some of the seeds remain dormant in the WSB as a back up opportunity to grow. In the case of Slender wild Oat, Avena barbata, it has two maturation ‘stages’ that take advantage of both early spring and late fall rains, with seed ripening at both of those seasonal times. Light is also necessary for many weeds to germinate. When weeds are removed by tilling or digging, new seeds are brought to the surface and may now germinate. Additionally, many weeds have the capacity to regenerate if the entire root is not removed. One tenacious weed, Field bindweed (Convolvulus arvensis), is known to regenerate from each node and root as deep as four feet. Cutting the plants into pieces makes more of them!

Weeds can be annual biennial or perennial . Some weeds such as Poa annua or annual bluegrass complete their life cycle (seed to seed) in only a few to several weeks, others grow for years. Annuals survive drought or cold winters as seeds while perennials as roots, tubers or dormant stolons or stems. Biennial weeds usually grow their vegetative body in the first year and reproductive structures in the second year, they are often rosette forming plants that grow close to the ground in the first season and develop tall stocks in the second. Knowing how to identify weeds helps to understand their biology and ultimately control strategies.

Many gardeners are herbicide averse. However, herbicides will often give the most economic and effective control of weeds. Some weeds like field bindweed are only well controlled with herbicides. Herbicides are broken down into two categories: pre-emergent herbicides and post emergent herbicides. Pre-emergent herbicides inhibit seed germination or kill emerging seedlings before they can develop. Post emergent herbicides kill weeds after they emerge from their seeds. Almost all weeds are better and more easily controlled at juvenile life stages. This is true for mechanical or chemical control. Regardless of how you choose to deal with the WA in your garden starting when weeds are small will give you a tremendous advantage.

Like all pesticides, herbicide labeling must be followed carefully to apply the right amount of product at the right time to the target weed (which also must be listed on the label). There are some amazing herbicidal tools that can save hours of labor. Some drawbacks of herbicides are that they may be expensive, may require multiple applications, require equipment to apply as well as personal protective equipment. Herbicides can be selective or broad spectrum. For instance, Fluazifob-P-butyl (active ingredient of Fusilade II) will control warm season grasses in many ornamental broadleaved plants. This is immensely useful since you can apply Fluazifop-P-butyl “over the top” of a flower garden and free it of bermudagrass (Cynodon dactylon) without harm to your ornamental garden plants or other non-grass landscape plants. Other herbicides containing plant growth regulators such as 2,4-D are broad-spectrum and will kill or harm many kinds of broad-leaved plants in turfgrass without harming the turfgrass. There are also some broad spectrum contact herbicides made of soaps or acids that will kill both broad leaved and grass weeds on contact. While these products do not have systemic action they can be very effective on both cool and warm season young weed seedlings. Herbicides when used carefully and following labeled instructions can save hours of hand weeding labor.

In my own yard I have chosen not to use herbicides because I have so many plants that are sensitive to the kinds of products I would need to use. I am pretty much down for other types of control. This month my city council decided to ban the use of gasoline powered lawn mowers–my chief weapon for the WA! We took a chance and used it anyway because our weed issues are so bad. As mentioned earlier the best time to use mechanical control of weeds is when they are in the cotyledon or two leaf stage of growth. A quick attack with a scuffle hoe will wipe them out. When they grow to adult weed size, larger and larger machinery become required.

Once perennial weeds such as bindweed grow a bit they become impossible to control with hoeing because they will grow back from roots. String line trimmers are used for weeding in many apocalypses but have their limitations. Bits of plastic trimmer line break off and pollute your landscape. Biodegradable plastics are usually used, but the idea of littering your yard with plastic bits is bothersome. Limiting the use of oil consuming machines is a great idea, but using battery powered machines has limits. Buying extra batteries so you can destroy while you charge is helpful.

Hand pulling is a great way to release pend up stress (of the human not the weed), get exercise, and rid the garden of apocalyptic pests. However, for some weeds like yellow nutsedge (Cyperus esculentus) you will only increase the problem as nutlets are released from dormancy when you pull the “mother” plant. By the time you see the emerging nutlets they have formed more nutlets so you can never get ahead of the problem. If you decide hand pulling will work, irrigate the day before you want to weed and they will come out much easier.

Mulching with fresh coarse arborist chips is a great way to prevent annual weeds from getting the light they need to germinate. Mulches also break down to improve soil. We have been mulching for a couple decades on my driveway but have not added any mulch for a few years. The broken down mulch and improved soil are now the most apocalyptic weed garden. If you use mulches for weed control fresh chips need to be applied at least annually in a thick layer to be effective. Also constant application of mulches can make soil! This soil builds up without you realizing that the root collar of perennials or trees may be getting buried. If you mulch consistently around trees be sure to keep the root collar exposed.

Not all weeds germinate in the early winter. There are winter and spring or summer germinating weeds. The differing timing of their emergence can happen unexpectedly. Just when you thought you had weeds in control, another set seems to appear requiring your attention. Look for summer emergent weeds when night temperature lows are above 60F.

Solarization is another way to kill weeds. This is the old greenhouse effect used as a weed weapon. Clear plastic laid on the soil surface and sealed at the edges will if exposed to full sun heat the contents to the point of their death. The solarization effect does not penetrate deeply into soil, so if perennial weeds are solarized, they may survive and regrow from root pieces. If you want to try solarizing your weeds purchase thick UV resistant plastic otherwise you will have bits of plastic everywhere as the sun breaks it down into pieces… Warning, this does not work with Field bindweed! In my own yard I have used old glass shower doors to solarize the soil.

Finally if all else fails and the WA is bearing down, you can just eat them. Many weeds are edible and can make good food. Nettle, Sonchus (sow thistle), purslane, dandelion and many of the Mustard family are edible at various stages of their development. Some folks have even collected mustard seeds and made their own condiments. Of course, you should always exercise caution when consuming wild foods. Some contain toxins or other chemicals that individuals may be sensitive to. The Sow thistle and wild lettuce (Lactuca spp.) contain latex which many are sensitive to. The stinging nettle has hairs on its surface that contain an irritant (oxalic acid) that causes skin burning and welts. Others, such as black elderberry may contain cyanide alkaloids in the green tissues-stems, fruit and other parts. Research the risks of consuming or contacting some plants before attempting to eat or handle them.  There is hope, because even the nutlets of one of the worst weeds (yellow nutsedge) are edible…