Drought Tolerance Versus Container Gardening

Drought tolerant plants loathe root confinement.

There are probably just as many reasons to not grow plants in containers as there are reasons to justify container gardening. Some potted plants consume less water than they would in the ground, but only because their demand is proportionate to their limited size. They only want more water in the ground because they can grow larger.

The most drought tolerant of plants are actually the least practical for pots or even large containers. They tolerate drought because they efficiently disperse their roots so extensively. Since they can not adequately disperse their roots in pots, they rely on what they can get from a relatively limited volume of soil. However, even if watered generously, many drought tolerant plants simply can not produce enough finely textured roots to absorb enough moisture.

For example, eucalyptus trees want to begin dispersing their roots while very young. If confined, their long and wiry roots simply go around within their limited volume of soil, trying to find a way out. They can develop a few more fibrous roots than they typically would, but probably not enough to compensate for limited root dispersion.

Wild lilac (Ceanothus spp.), flannel bush, manzanita and smoke tree are not only sensitive to confinement, but have difficulty recovering from confinement if put into the ground after their roots have circled too much within a container. Pines and many other conifers are likewise sensitive to confinement, but some types can recover if the binding roots get severed before they go into the ground.

Plants with dense and fibrous roots are more adaptable to containers. Most succulents and common yucca are good choices. Ferns and some grasses also work nicely, but need to be watered rather regularly. Some types of arborvitae and juniper work better than larger coniferous evergreens. Some small bamboos can stay potted, but not larger types.

Annuals, compact perennials and many ground covers that provide color and fill in space around larger plants are naturally adaptable to container gardening, but their need for regular watering can not be denied. There simply is no practical way of combining container gardening and drought tolerance.

Roots Prefer To Roam Freely

Some yuccas are unhappy in pots.

Roots are innately mysterious. They consume much of the resources that plants require. They stabilize the stems above them. Few plants can survive without them. Yet, roots are very secretive about their work. Almost all are invisibly subterranean. Consequently, they get minimal consideration. A lack of consideration is a root cause of many root problems. 

Every plant species has distinct environmental preferences. Some plants require full sun exposure. Others tolerate or prefer partial shade. Some are more discerning than others. Similarly, plants that naturally disperse their roots extensively dislike confinement of their root systems. Small plants and some riparian plants are more adaptable to confinement.

Annual bedding plants and many small perennials perform well within pots, planters and small spaces because they do not need to disperse their roots extensively. Some woody plants with fibrous root systems, such as azalea, boxwood and andromeda, can adapt to confinement also. Occasional pruning can keep them proportionate to their root volumes. 

Most of the popular succulents perform remarkably well in confinement. Some types that disperse their roots extensively if necessary will adapt to confinement by dispersing their roots only as far as they must. If they get all they need within a pot, they need not go any farther. However, succulents that are endemic to dry desert regions are not as adaptable. 

Desert plants can survive warm and dry summers because they disperse their roots very extensively. They can not do so within the confinement of pots and planters. This should not be a problem that systematic irrigation can not compensate for. Unfortunately though, these same plants are too susceptible to rot if their roots are damp during warm weather.

So, some plants that are the most resilient in the ground are the least resilient in pots. Of course, this is not an absolute rule. Yuccas from tropical and temperate climates perform well either in the ground or in pots. Those from desert climates are likely to rot in pots. In general, drought tolerance and container gardening are two fads that are not compatible. 

Horridculture – Solar Power

This gives a new meaning to ‘shade tree’.

Leaves are the original solar panels. They collect solar energy, and convert into useful resources. Some of those resources get converted into other resources that are good for human consumption, such as fruit, vegetables, lumber, firewood and oxygen. However, one resource that leaves do not produce is electricity.

That is why the big solar array pictured above was installed over a big parking lot. There are a few of these arrays in this parking lot, and more in other nearby parking lots. Many trees were cut down to accommodate them. People who work nearby can use the electricity more than they could use vegetation, or anything that vegetation could produce within this area.

Shade trees are nice over parking lots, but are not necessary over a parking lot that is shaded so thoroughly by such big solar arrays. After parking during rainy weather, an umbrella is only necessary between the solar arrays and the adjacent office buildings. There are no more fallen leaves to clean up. Pavement and curbs will no longer be displaced by growing roots.

The red gum that is also pictured above, under the solar array, is not so impressed. It likely grew from a root of a red gum that was removed so that the solar array could be constructed. Sadly, it must be cut down again, not only because it is under the solar array, but also because it is against the sidewalk. It has clearance problems both above and below.

It is rather ironic that even after all the trees that formerly shaded this parking lot were cut down for the installation of this solar array, this young red gum that is so determined to survive can not stay. I can not help but wonder what this young red gum thinks of green energy.

Summer Is Not For Planting

New plants are less reliant on irrigation if installed at the beginning of the rainy season.

Autumn is the time for planting. Cooling weather slows plants down so that they do not mind disruption so much. Increasing rain (hopefully) keeps the soil evenly moist while roots slowly disperse. The combination of cooling weather, increasing rain and shorter days keeps plants well hydrated so they can slowly ease into spring.

Why is this important now? Well, it probably is not important. It merely demonstrates why this is not the best time for planting. Only a few warm season annuals and vegetables get planted this time of year. Seeds for certain autumn vegetables get sown now. Otherwise, more substantial plants should wait until autumn if possible.

Mid summer in some ways is the opposite of autumn. While the weather is warm, plants are too active to be bothered. Even minor disruption can be stressful. Soil moisture provided by irrigation is often too irregular and unreliable for dispersion of many new roots. There is less time to recover from stress during shorter nights.

Smaller plants and seeds survive summer planting better than larger plants do. Seeds need to disperse all new roots anyway, so they  will adapt to what they get. They certainly need regular watering, but are quite talented at putting their roots wherever the moisture goes. With a bit more time, smaller plants will do the same.

Larger plants have more difficulty with the planting process because they need to disperse so many more roots to get established. When they get planted, all their roots are initially confined to the volume of media (potting soil) that they were grown in. They are susceptible to whatever happens within  that limited volume.
For example, a small plant in a four inch wide pot is initially confined to less than sixty-four cubic inches of soil. It can double its soil volume to one hundred forty-four cubic inches by merely dispersing roots less than one inch laterally. A tree in a 24-inch wide box needs to disperse roots ten inches laterally to do the same!
It would seem that drought tolerant plants would be less susceptible to the stress of planting in summer.

However, they are more sensitive because they are so reliant on extensive root dispersion. Until they disperse their roots, they actually need to be watered as frequently as other plants do.

Figs Are Easy To Propagate

Some grasses can propagate by division.

The easiest way to propagate new fig trees may seem to be violent, but it works. Basal shoots that grew last year from the roots near the trunks of ungrafted trees can simply be torn out of the ground with as many attached roots as possible. These shoots can then be planted directly wherever new trees are desired, and watered in. Larger shoots may need to be dug out, and might do better if pruned down to just a foot or two tall when planted. Smaller shoots can be potted to grow through next summer, and then get planted in the ground next winter.

Tearing the shoots off in this unpleasant manner is effective for two reasons. It gets the most roots for the shoots to help the grow into new trees. It also removes more of the burl growth that produces the shoots than simply cutting the shoots neatly. Even if copies of the original tree are not desired, the basal shoots must be removed anyway. Simply pruning them away leaves more burl growth so that more shoots grow back next summer. Ideally, well maintained trees should actually not produce basal shoots.

Fig trees are innately easy to grow from basal shoots or cuttings while dormant through winter. Basal shoots, even those that get pulled without any obvious roots, will develop roots more efficiently than stem cuttings that were never in contact with the soil. However, if no basal shoots are available, stem cutting work just fine. Furthermore, grafted trees (which are quite rare) can only be copied by cuttings from above the graft. Basal shoots from below the graft will only produce copies of the understock.

Just as unwanted basal shoots and cuttings from pruning scraps can be grown into fig trees, overgrown perennials in need of thinning can be divided to propagate more of the same. Lily of the Nile, red hot poker, daylily, mondo grass, African iris, terrestrial yuccas, some ferns and some grasses are not only easy to propagate by division through winter, but many perform better if divided every few years or so, before they get too crowded. The common giant yucca develops big trunks instead of clumping shoots, but can be propagated just as easily from big cuttings.

Planting Bare Root Stock Properly

Bare root roses bloom next summer.

Most of the advantages of bare root stock are obvious. Bare root stock is less expensive and easier to work with in regard to installation and pruning to a desired form. What some of us may find difficult to understand is that it actually gets established into a new garden more efficiently than canned (potted) nursery stock does. As incredible as it seems, there are a few simple reasons why.

Instead of dispersing roots within the confinement of cans, bare root stock disperses roots directly an extensively into the soil into which it gets planted. Their initial deficiency of roots encourages them to do so quickly. Roots of canned stock must recover from confinement. Their new roots may be hesitant to leave the comfort of the extra rich medium in which their original roots developed.

The holes dug for planting bare root stock need not be much wider than the roots can be spread apart, and no deeper. If too deep, newly planted stock will sink as the loosened soil below settles. Grafted plants must not sink enough for their graft unions to be below grade. A cone formed of firmly pressed soil at the bottom of a planting hole can be useful for spreading roots out evenly over.

Rich soil needs no amendment. If compost is added to loosen dense soil, it should be as minimal as practical. Too much amendment will tempt roots to stay close rather than dispersing remotely. Fertilizer is not necessary immediately after planting. However, because the soil does not stay very cold here, and roots start growing before spring, mild fertilizer can be applied shortly afterward.

Finally, most bare root stock should be groomed and probably pruned after planting. Fruit trees are often sold with only minimal prior pruning. Superfluous stems function as packing material that buffers the ravages of transportation, and also provide more options for preliminary structural pruning. Aggressive pruning of plants that benefit from it concentrates resources for growth in spring.


P90901It has been almost a month since one of three small but sculptural and very prominent coast live oaks at work was destabilized by . . . well, children. They were climbing on it, as most good children should do. There were a few of them; and the tree is old and deteriorating. All three of the trees actually grew from the same rotten stump of a tree that was cut down decades ago.

I wrote about it at ‘Six on Saturday – Do Not Sit On Tree‘. The title will make more sense if you read about it.

To salvage the tree, I pruned off as much of the foliar canopy as possible. This eliminated some of the weight that the trunk needs to support, as well as decreased some of the resistance to wind, which exerts leverage against the compromised root system when wind blows. Sawhorses were placed under the trunk, and one of the others, to prevent them from sagging any lower.

Props that were fabricated to be more permanent then the sawhorses were installed last week. They do not actually support or even touch the trunks, but are there to prevent the trunks from sagging any lower. If the trunks start to lean on the props, I will prune a bit more weight off. If that doesn’t work, the props can be moved a bit farther out, where the trunk are higher.

Hopefully, the old root system of the destabilized tree was not so severely damaged that it can not recover. If it does recover, and the trunk is not supported by the new prop, the tree will need to eventually regain stability. It will be a tediously slow process. Because the trees are already so mature and disfigured, the props will likely never be removed, regardless of recovery.

The first picture above show the destabilized tree outfitted with a new prop. The second picture below shows the other tree that was outfitted with a new prop just because it is so likely to become destabilized.


To Mulch Is Not Enough

60727thumbMost plants would prefer the real thing; how they do it in the wild. They drop their leaves, flowers and twigs. Deciduous plants do it mostly in autumn. Evergreens might spread it out through the year. The debris accumulates on the ground below, and decomposes at about the same rate as it accumulates. There is no one there to clean it up. Yet, the natural ecosystems know what to do.

The plants that produce the debris use the nutrients produced by its decomposition. So, with the help of the many microorganisms in the soil, they recycle their own trash. To exploit this resource most efficiently, feeder roots tend to congregate near the surface of the soil where the nutrients are. Because the debris also insulates and shades the soil surface, roots are comfortable there.

Densely forested ecosystems produce the most debris. Many smaller plants in such ecosystems may disperse their roots exclusively into decomposing debris without reaching into soil below. In desert ecosystems, where such debris is minimal, roots are mostly dispersed much deeper to avoid the hot and dry soil surface. They wait for recycled nutrients to leach to them through the soil.

Redwoods, cypresses, many pines and most eucalyptus produce unusually thick layers of debris that decompose slowly. This technique inhibits or prevents the germination of seeds of potentially competitive plants. So, in other words, these trees and other plants had this, as well as moisture retention, soil insulation and nutrient recycling, all figured out long before we knew about mulching.

After we put so much work into raking and disposing of foliar debris that would otherwise accumulate in our gardens, it is ironic that we sometimes need to apply seasoned mulch to compensate for the lack of organic material on the surface of the soil. (Unseasoned mulch draws nitrogen from the soil to sustain its own decomposition.) It does more than merely improve the appearance of otherwise exposed soil. Mulch helps unnatural landscape environments function a bit more naturally.

Horridculture – All Wet

P90327Regardless of their individual innate requirements for water, new plants need to be watered very regularly immediately after they are installed into a landscape. As they mature and disperse their roots, the regularity of supplemental watering becomes less important, and ‘drought tolerant’ plants may not need to be watered at all. Maturing larger trees generally get what they need from the landscape around them.
Automated irrigation systems that are designed for new landscapes are designed for what the plants need while the landscapes are new. As the landscapes mature, the irrigation systems may need to be adjusted accordingly. Drip irrigation or bubblers that were needed to water new trees while they were young and confined should be moved farther from the trunks of the trees as roots disperse, and should eventually be removed and capped.
This is very important, since water applied directly to the trunks of some maturing trees will promote rot and other disease. For some, it promotes buttressing of roots that can displace concrete or other landscape features. If nothing else, it is just a waste of water.
Whoever installed the irrigation to this young London plane tree knew how to do so properly. The bubbler was likely over the confined root systems of the formerly canned tree just after it was installed. It is installed in such a manner that it could have been moved over as the tree grew, replaced with some sort of drip irritation hose to curve around the tree (if such a device had become necessary), or simply removed.
Now that the tree is as mature as it is, the bubbler should simply be removed, and the riser (where the white ‘L’ is) should simply be capped. The tree gets what it needs from the rest of the landscape around it, and really does not need much water anyway. It could probably survive without any supplemental irrigation at all. The bubbler is really just wasting water.
However, because so-called ‘gardeners’ are what they are, the bubbler remains, attached to an unsightly bit of exposed pipe, and wasting water on the base of the trunk of the sycamore. Because this tree and associated bubbler are right next to a parking spot in a parking lot, the pipe is very likely to get stepped on and broken every once in a while. In fact, the fresh Teflon tape on both ends of the pipe suggest that it was repaired quite recently, rather than removed.
Fortunately, the sycamore will not likely be damaged by water applied directly to the base of the trunk.


P90216KToday’s episode is brought to you by the letter ‘T’.
This is not Sesame Street.
Nor is this freshly painted concrete ‘T’ a monogram that designates the garden as mine. Even I am not ‘that’ vain.
It is part of a sign at the train depot. There happen to be enough of the right letters for my last name. I suppose that with a pry bar and a shovel, I could be ‘that’ vain.
There is no ‘Y’, so my first name would not work, particularly in conjunction with my last name, which would take the only ‘T’ and ‘O’ available. Am I really vain enough to be putting this much thought into this? Oh my!
For right now, I should only be concerned with keeping the vegetation clear of the sign. The amaryllis foliage above barely flops into it. The overgrown photinia hedge behind the amaryllis was just removed. The arborvitaes that will be installed to replace the photinia hedge will not likely get wide enough to ever reach the sign. They will be set several feet back. We are still trying to decide what to install between the arborvitaes, which will be far enough from each other so that they will not become a continuous hedge like the photinia were.
You would not believe how many bay trees and valley oak trees were trying to grow amongst the photinia! They ranged in size from fresh seedlings all the way up to a nearly six inch wide coppiced stump of a valley tree that was cut down a few years ago. There are still a few small oaks that must be removed nearby. We want to remove them while we are working on the site, and before they get big enough to displace the concrete letters with their roots.