Taking It To The Streets

Tipu tree is the topic for tomorrow.

No matter how unique the individual gardens are, conforming street trees really unify a neighborhood. Streets of tract homes are typically planted with a common street tree that is complimentary to the architectural styles of the homes, and is complaisant to the difficulties of life at the curb. Neighborhoods of mixed architectural styles sometimes have difficulty finding a tree that suits every home, so often select two or more options. Older neighborhoods are not quite as selective about conforming street trees because so many various trees get mixed in over the years.

Before selecting a street tree, it is best to inquire with the particular municipality about designated street trees. Home owners associations generally install their own trees where needed, with little or no regard for the preferences of individual residents. Some urban neighborhoods (that are not home owner associations) are nearly as selective, requiring individual home owners to maintain a specific street tree or trees. Others do not require street trees, but limit selection for those who desire them. Selection is very often limited to only a single species.

There are of course many rural and unincorporated neighborhoods without limitations for street trees, and neighborhoods where limitations simply are not enforced. However, selection should still be limited to trees that are appropriate for curbside planting. Such trees should have high branch structure so that they can be pruned for clearance above the largest of trucks that can use the roadway. They should be reasonably clean, and not produce anything that could be messy on cars parked below. Roots should be complaisant with concrete curbs and sidewalks, particularly where space is limited. Foliage and bark must be resilient to harsh exposure and enhanced glare (from surrounding pavement).

London plane (sycamore) and crape myrtle trees are the two most common street trees planted by landscapers, and are the most commonly pre-designated street trees, but are actually not the best of choices. London plane is popular among landscapers because it can survive the neglect that landscapers are notorious for, but has aggressive roots that eventually damage concrete, especially since landscapers waste so much water and keep the soil saturated. Crape myrtle is remarkably colorful both in bloom and with fall color, and has remarkably complaisant roots, but does not get tall enough for adequate clearance, and often gets infested with insects that drop sticky honeydew on parked cars.

This was the topic for yesterday.

Drought Tolerance Necessitates Root Dispersion

Extensive root dispersion enhances drought tolerance.

Fads certainly complicate gardening. Most are merely marketing tactics. Most are bogus. Many even contradict their justifications! For example, most new, trendy and supposedly sustainable plant cultivars are genetically weak because of extensive breeding. Drought tolerance likewise has potential to be a constructive fad, but is so commonly misapplied.

Incidentally, its terminology is somewhat inaccurate. Drought is an extended but unusual pattern of dry weather. Whether the duration is for one year, or many, it is not permanent. The dry weather that persists through summer locally is normal for the chaparral climate. It is therefore a normal characteristic of climate, rather than abnormal weather conditions.

Drought tolerance is therefore practical here as chaparral tolerance. Most plants that are drought tolerant are naturally endemic to chaparral regions or deserts. Many of the native species naturally exhibit remarkable drought tolerance. Once established, they might not require any more moisture than they get from annual rainfall. Some prefer dry conditions.

Drought tolerance should not imply that such plants are undemanding. In some regards, they are more demanding and less adaptable than plants that require frequent watering. Such plants rely on extensive root dispersion to procure the moisture they require within dry situations. Most do not adapt to confinement, even if watering is enough to cause rot.

Container gardening is therefore a fad that is incompatible with drought tolerance. It only uses less water for plants that use more water. Also, modern drip irrigation, which is very practical for plants that rely on irrigation, requires a bit more effort for plants that use less moisture. To not promote rot, emitters must move farther from main trunks as plants grow.

Many of the most sustainable and drought plants are old fashioned sorts that became too common years ago. Fortunately, some are regaining popularity again. Some of the more compact eucalypti are proportionate to modern gardens. Grevillea, bottlebrush, rockrose, juniper, rosemary, salvia, lavender and New Zealand flax are as drought tolerant as they had always been.

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

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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

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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

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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

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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.

Props

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.

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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.