The Wrong Time For Pruning

80801thumbNot many plants are sensitive to mere heat alone. Actually, many plants prefer warm weather. The difficulty that some plants have with heat locally is that it typically accompanies aridity, and often accompanies afternoon breezes. As appealing as breezes and minimal humidity are to us while the weather is warm, they promote and accelerate desiccation of exposed sensitive foliage.

Pruning, which obviously becomes necessary while warm weather promotes growth, can make plants more sensitive to damage caused by warm, sunny, arid and perhaps breezy weather. It exposes formerly sheltered stems and inner foliage, which are more sensitive than outer foliage is, to more sunlight and drying breezes. Exposed foliage can either desiccate or roast, or both!

A bit of unsightly but relatively minor foliar damage on the extremities of the outer canopy might be only superficial, but major damage can be dangerous. Superficial damage often gets replaced by fresh new growth before it deteriorates enough to expose more foliage and stems below. However, recovery from major damage can be delayed by the distress associated with the damage.

Japanese maple, aralia, philodendron, rhododendron and all sorts of ferns can easily get damaged by increased exposure. Low ferns are not likely to become too exposed by any loss of their own foliage, but often become more exposed by the pruning of plants above them. Like frost damage, foliar scorch might need to be left to shelter remaining foliage until new growth develops.

The bark of many plants, although not susceptible to desiccation, is very sensitive to sun-scald if too exposed. Young and smooth bark is the most sensitive, particularly if it had always been shaded. Scald kills bark and the vascular tissue below. As it decays, it exposes interior wood to more decay that is likely to compromise the structural integrity of the affected stems and trunks.

Pruning during relatively cool weather and while there are a few relatively cool days in the forecast allows foliage a bit of time to adapt to a new exposure before the weather gets dangerous. Through summer, pruning should not be so aggressive that too much sensitive foliage or bark are exposed, even if it is necessary to leave a bit of unwanted sloppy growth to partly shade bark. Aggressive pruning of exposed and sensitive plants should be delayed until autumn, when sunlight is not so intense, and weather is cooler and wetter.


Six on Saturday: Oh, The Shame!


Not my shame of course; but that of the trees in the pictures below.

Do not try this at home. I only did it because I am a horticulturist and arborist; and I happen to be one of the last arborists in America who condones coppicing and pollarding, which are depicted here.

Coppicing is cutting trees or shrubbery down to the ground annually, or at least regularly every few years or so. Some coppiced trees form basal burls or lignotubers. Some just form thicket growth that replaces itself after getting coppiced back to the ground.

Pollarding is similar to coppicing, but rather than cutting all growth back to a stump or stumps at ground level, it involves pruning all growth back to the same distended knuckles at the ends of a few main limbs annually, or at least regularly every few years or so. It is done in such a manner that the pruning wounds are compartmentalized by the new growth of the following year. Knuckles can be elongated by leaving single short stubs.

There are a few reasons for coppicing and pollarding. Some subjects develop an abundance of appealingly lush foliage. Some develop an abundance of appealing or useful twiggy growth. Coppiced red twig dogwoods are much twiggier and more colorful while bare in winter. Pollarded or coppiced willows produce an abundance of canes for basketry. White mulberries are pollarded to provide an abundance of lush foliage to feed silkworms.

I coppiced a Eucalyptus globulus ‘Compacta’ and pollarded a Eucalyptus globulus for two main reasons. Both are such problematic trees that I do not want to plant either into the ground, so must keep them contained. Also, I want the remarkably aromatic juvenile foliage that develops in response to coppicing and pollarding.

1. Eucalyptus globulus ‘Compacta’ coppiced stump. It is not such a great example of a coppiced stump, since the tree did not grow enough two years ago to get coppiced last year. Consequently, the few main trunks that were just recently coppiced are already starting to form their own separate lignotubers on top of the original, which is now rotting below. Soon enough, they will fuse to form a single lignotuber, concealing the evidence.P90601

2. Eucalyptus globulus ‘Compacta’ before getting coppiced. It is quite small for a specimen that was not coppiced last year.P90601+

3. Eucalyptus globulus ‘Compacta’ after getting coppiced. Rhody is not impressed.P90601++

4. Eucalyptus cinerea in need of pollarding. This tree grew too big too fast to survive any longer in the relatively small #15 (15 gallon) can. Fortunately, in just a few days, it will instead get installed into a landscape where it can disperse roots and mature into a normal unpollarded tree. After a few years, it might get pollarded anyway, just to produce silvery juvenile foliage withing reach of the ground, but that is not a concern just yet.P90601+++

5. Eucalyptus globulus pollarded knuckle. This is only the second pollarding procedure for this subject. The first procedure involved lopping the lanky single trunk off right here where the knuckle is now. The multiple limbs that developed were just recently lopped off, leaving this distended knuckle to repeat the process, hopefully annually.P90601++++

6. Eucalyptus globulus pollarded trunk. This is why Eucalyptus globulus should not get pollarded! They look ridiculous if deprived of their naturally elegant form. They do not look much more dignified with multiple pollarded limbs. Oh, the shame!P90601+++++

This is the link for Six on Saturday, for anyone else who would like to participate:

Spontaneous Limb Failure Is Real

90605thumbIt sounds like science fiction, but it is not. Every spring and during particular summer weather, limbs can fall from trees without warning, and seemingly for no reason at all. It happens when least expected, while the weather is warm and perhaps humid, but notably without wind. The lack of wind is what makes it so unexpected. It is a phenomenon known simply as spontaneous limb failure.

Those who witness it might think that the arborists they call to clean up the mess will not believe their descriptions of what happened. Yet, arborists are familiar with it. Quite a few species of trees are notorious for it, especially in urban landscapes where they get watered regularly. Most of such trees are either chaparral trees that do not expect much water, or riparian trees that do expect it.

Spontaneous limb failure occurs as warmth accelerates vascular activity, but humidity inhibits evapotranspiration, which is evaporation from the foliage. Accelerated vascular activity increases the weight of the foliage. Inhibition of evapotranspiration limits the ability of the foliage to eliminate some of the excess weight. Limbs break if unable to support the increasing weight of the foliage.

Spontaneous limb failure is not as easy to predict as the more familiar sort of limb failure that is caused by wind. Limbs that get blown down typically exhibit some sort of structural deficiency or disfigurement prior to failure. Some limbs that succumb to spontaneous limb failure do so as well, but most do not. They just happen to be the healthiest and most densely foliated parts of a tree.

Native coast live oak and valley oak are the two most familiar of the chaparral trees that are notorious for spontaneous limb failure. Native cottonwood, willow, box elder and sycamore are riparian trees that are perhaps even more susceptible to spontaneous limb failure. Sweetgum, carob, stone pine and various eucalypti are some of the exotic trees that might drop limbs spontaneously.

In summer, spontaneous limb failure is less likely as growth slows and limbs strengthen.

Roses Can Not Be Neglected

P80602+Roses are not for the meek. They are too demanding, too sensitive, too thorny, and without their flowers, they are not even very attractive. They have no business in a low-maintenance landscape, or in a landscape maintained by mow, blow and go gardeners. Those who want to grow rose plants for their flowers should be ready to give them what they want, and to prune them aggressively.

The most aggressive pruning gets done during winter dormancy. That process alone can be quite intimidating for those who are just getting acquainted with roses. After seeing them grow through the year, it seems counterproductive to prune big plants back to only a few short canes. Yet, by now, those canes should have produced much taller new canes that are already blooming profusely.

Now it is time to prune roses again, or will be time to do so soon. Deteriorating flowers need to be pruned away to promote continued bloom, a process known as ‘deadheading’. Otherwise, the fruiting structures that develop, known as ‘rose hips’, divert resources and inhibit bloom. Of course, blooms taken as cut flowers leave no hips, but they might leave stubs that may need grooming.

The popular technique of pruning back to the fifth leaf below a hip is not necessarily what roses want. It probably originated from the recommendation of pruning back to a low leaf with five leaflets because the buds associated with upper leaves with three or less leaflets are not as likely to develop into productive stems. However, pruning a bit too low is probably better than pruning too high.

When cutting roses to bring in, it is better to cut long stems, and then shorten them later if necessary. Each stem should be cut just above a leaf so that the bud in the leaf axil can develop into a new stem without much of a stub above it. The cut stem left behind on the plant should not be so long that it extends too far above the canes that were pruned over winter, or becomes crowded.

Crowded stems inhibit growth of vigorous blooming canes, and are more susceptible to rust, mildew and blackspot.P80602++

Horridculture – Bad Pollarding And Coppicing

P90508Pollarding and coppicing are proper pruning techniques. If you think you are an arborist who believes otherwise, do not waste my time arguing about it. More than likely, you are neither as educated nor as experienced as I am with such matters, or you work exclusively with trees for which such procedures would be very inappropriate.
Well, yes, pollarding and coppicing are very inappropriate for the vast majority of trees and shrubs out there. Furthermore, even for those trees and shrubs that they are appropriate for, such procedures are very rarely done properly here in California. Most attempts at pollarding and coppicing are really horrid!
Take these blue elderberries and mock oranges for examples. They were mutilated last summer to improve the view of the historic Felton Covered Bridge. It sort of accomplished that objective, although the improved view of the Bridge was then cluttered with the disfigured and mostly bare trunks and limbs of the brutalized shrubbery below. Because they were chopped back too late in summer to grow much, they stayed that way until now.
So it is spring, and the shrubbery is growing from the tops of the mutilated but tall trunks and limbs, right back to obstructing the view of the Bridge. They will likely get chopped when they get to be too overwhelming, which again, will be in late summer, repeating the process. It would be better to just remove the shrubbery not only because it would be less work, but also because the shrubbery is so unsightly when it gets chopped!
OR; the shrubbery could get coppiced. Both blue elderberry and mock orange respond favorably to the procedure. If coppiced, or in other words, if pruned back to the ground annually each winter, they could regenerate fresh new growth each spring, but not get big enough to crowd the view of the Bridge by the following winter, when they get coppiced again. The elderberry would not bloom or fruit; but that is not important here anyway.
Coppicing takes advantage of the natural dormancy and regenerative processes of the plants. Starting over fresh each spring and growing uninterrupted through summer is more natural for them than trying to recover from getting brutalized while they are actively growing in summer. Since they start the process at ground level, they have room to grow without interruption. If cut back only as much as necessary, they have no room to grow.


P90413KThis is the beginning of one of several new knuckles on a pollarded crape myrtle tree that was pollareded for the first time just this past winter. It was quite a mess of thicket growth that was too congested to bloom well. It is also located in a confined situation where it could not just be groomed, pruned up for clearance, and then just left to develop a larger canopy higher up. Pollarding will both contain it, as well as invigorate healthier growth.
New shoot growth now emerging from the ends of limbs that were pruned back last winter will elongate and eventually bloom through spring and summer. Next winter, after all the colorful autumn foliage has defoliated, the tree will get pruned back to these same knuckles to repeat the process. Stems will get cut back as neatly as possible, leaving no stubs, but such pruning causes knuckles to become slightly more distended as the develop.
Minor shoot growth that develops elsewhere on the mature stems below the developing knuckles should be removed as it appears. It is easy to knock off now, before it gets big enough to need to be pruned off. Knocking it off or ‘peeling’ it off, as drastic as it sounds, is actually better than pruning it off. It removes more of the callus growth that is likely to develop more stem growth later. New growth should be concentrated into the knuckles.
Pollarded crape myrtles bloom later than those that are not pollarded, but they bloom more profusely. They are also more resistant to mildew, and develop better foliar color in autumn.
The picture below shows the same crape myrtle that I got the picture of the single knuckle above from, shortly after it was pollarded. This picture was used another article at:

Way Beyond Last Frost Date

90410thumbScheduling of gardening chores is as important now as it ever was. We plant warm season vegetables and annuals in time for spring and summer. We plant cool season vegetables and annuals for autumn and winter. We pick flowers as they bloom. We harvest fruits and vegetables as they ripen. We watch the seasons change on our calendars, as well as in the locally specific weather.

Yet, the one scheduling tool that we do not hear as much about as we did when agriculture was more common in the region is the ‘last frost date’. It refers to the average date of the last potentially damaging frost for a specific region. The last of such frosts might actually be earlier or later, but the last frost date remains a standardized time to plan particular procedures and planting around.

There are likely a few reasons why we do not talk about the last frost date much. The most relevant reason is likely the timing. Around here, the last frost date is sometime in January. It is earlier in some spots, and later in others, but it is sometime between January 1 and 30. It is simply too early to limit much of what we do in the garden in early spring, and is irrelevant to most winter chores.

It might seem to be just as irrelevant now, since the last frost was so long ago. Seed for warm season vegetables and annuals is sown as the weather gets warmer only because it would grow too slowly while the weather is too cool in winter, not because of a threat of frost. There really is quite a bit of time between the last frost and warm spring weather, while the weather is still rather cool.

However, pruning of plants that were damaged by frost should have been delayed at least until after the last frost date, and perhaps as late as spring. Although unsightly, damaged growth shelters inner growth from subsequent frost. Besides, premature pruning stimulates new growth that is more sensitive to subsequent frost. Most of such pruning is delayed until just after the last frost date.

If delayed longer, fresh new growth will show how far back damaged stems must get pruned.

Sugaring Season

P90316KThere is no sugaring season here. Spring comes on too suddenly. By the time sap starts to flow, buds are already swelling.

Bigleaf maple, Acer macrophyllum, happens to be native here, although it is not common. It is the sugaring maple of the Pacific Northwest. A tree next to my driveway gave me enough sap to boil about four ounces of maple syrup a few years ago. That was all I needed to make the point to my colleagues who insisted that it could not be done that it really could be done.

Box elder, Acer negundo, is also native, and in riparian zones, is much more common than bigleaf maples is. I am told that is provides sap for sugaring just like any other maple does. Some say the sap is of inferior quality, or boils to cloudy syrup. Others say that it is comparable to that of any other maple.

Now that I made my point about getting a tiny bit of syrup from a bigleaf maple tree, I have no intention of sugaring again. However, sugaring season is still something that I need to be aware of. It is when I can not prune the maple trees. I can prune them earlier in winter or later in summer, but not while they are most vascularly active during sugaring season. Otherwise, they don’t stop bleeding. Even if the bleeding is harmless, it is unsightly if it stains the trunks and becomes infested with sooty mold as the weather warms.

The same rule applies to birch trees.

I pruned a few of the European white birch, Betula pendula, at work last week, believing that it was still too early for them to be too active. It was not much at all, and involved only a few small upper limbs and two significant lower limbs that had been disfigured by pruning for clearance from adjacent utility cables. I did not notice bleeding from the small stubbed limbs that I pruned from high in the canopy with a pole saw. Yet, the sap started to pour from the pruning wounds before I finished cutting away the two larger lower limbs that happened to be on the same tree. They are still bleeding now. In fact, they are bleeding so much that I feel badly that the tree is losing so much sap. If I had known how much sap would bleed, I could have put a bucket under each of the two wounds to catch the sap to make a small bit of syrup as is done in Alaska.

Pruning Late Might Be Justified

90313thumbThere may not be exceptions to every rule, but there are a few exceptions to the rule that winter is the best time for pruning. It is generally true that most plants are the most dormant through the coolest part of winter. It is also true that while they are the most dormant, most plants are less sensitive to pruning, as well as other horticultural techniques that interfere with their normal function.

However, certain ‘special’ plants get pruned later, either because it is healthier for them, or just because they are allowed to do what they do best in spring before getting deprived of some of what they need to do it with. Some get pruned rather soon after coming out of winter dormancy. Some should probably wait for their new spring growth to mature a bit. It is not as confusing as it sounds.

Evergreen plants that drop much of their older foliage through winter should probably be pruned late in winter or early in spring, essentially at the last minute, just before new foliage develops. If shorn early and deprived of outer foliage that should survive through winter, photinia looks scraggly as it continues to lose much of what had been inner foliage until new foliage develops in spring.

Red twig dogwood and some types of willows that are coppiced or pollarded to maximize production of their colorful twigs should be allowed to show off their colorful bark for as long as possible. Like photinia, they too can be pruned at the last minute, just before vascular activity resumes. However, red twig Japanese maple really should be pruned in winter so it does not bleed afterward.

Flowering cherry, plum, peach, crabapple and quince are grown for prolific but sterile bloom which is diminished by winter pruning. If they need it, they can instead be pruned after bloom, but before too much foliage develops, or after such foliage matures in late spring or early summer. They do not need to be pruned nearly as aggressively as fruiting trees that would otherwise produce too much burdensome fruit. Some may only need to have dead stems pruned out.

Bullwinkle II

P90303What makes this Bullwinkle worse than most is that I pruned it like this myself. What makes it worse than worse is that it did not need to be pruned in this disfiguring manner for clearance from utility cables like the last one I wrote about was. It is instead an attempt to renovate an overgrown hedge that was behaving something like a fat hedge.

In fact, the only reason it did not qualify as a fat hedge is that it had plenty of space for all of its superfluous bulk The side to the left was only beginning to encroach into the driveway on that side, and was easily pruned back to the curb, which for now, is adequate confinement. The side on the right was only beginning to encroach into the upstairs balconies, and was likewise easily pruned back for reasonable clearance.

The problems with this hedge were within and on top. It had been shorn back only for minimal confinement for so long that all the foliage on the sides was within a thin external layer. Pruning any farther back would have exposed a thicket of necrotic stems in various degrees of deterioration that had been accumulating within the interior for many years. Almost all growth was directed to and concentrated on top, which shaded the interior and lower stems even more than the accumulation of necrotic crud within did. Since the top had always been pruned down to the same height, all subsequent growth after pruning on top was above where it had been pruned previously, which was of course above the height where it was wanted, and consequently removed when the hedge was pruned again. There was no incentive for lower foliage to develop.

The hedge is there to obscure the view of a building on the left from the windows of the building on the right. The most important foliage for that purpose is the lower foliage, which is precisely what is lacking. Almost all resources were going to the upper foliage, which was contributing nothing, while shading out the lower growth. Although the inner thicket of necrotic stems was partially helping to obscure the unwanted view, it was also inhibiting healthier lower growth.

The illustration shows what remains after the useless top and necrotic interior were removed. After the picture was taken, the left and right sides of the hedge were pruned lower to eliminate the useless upper foliage that was not contributing to the function of the hedge. As unsightly as it is, it partially obscures the view of the building on the left from the building on the right, and will obscure it more as new foliage develops. Now that the interior is exposed, new growth should develop within the interior, and lower to the ground. Because the area is partially shaded by nearby redwoods, the exposed interior limbs are not likely to be damaged by sun scald.

After the new interior growth is established and obscuring the view, the external sides that are there now can be pruned back farther and sloped inward toward the top so that the lower growth of the hedge gets more sunlight. The hedge certainly does not need to be as wide as it is. It would be easier to maintain if it were narrower and so close to the allowable boundaries. Ultimately, with appropriate pruning over the next few years, this old hedge should be restored.