When the George Landis Arboretum was started in 1951, they had three summers of extreme drought.
The plantings, all young and susceptible, have served as a compact laboratory in which to observe the ability of many kinds of trees and shrubs to withstand dryness under field conditions.
Practical Methods of Spotting Specimens
At the same time, we have learned how to spot specimens that are in danger and what some practical methods for saving them are.
Some of these facts may be of value to homeowners who are naturalizing waste spots on the edges of their property.
Likewise, city dwellers with summer places, who visit them only on weekends and wish to preserve what they have planted may find this information helpful.
Ages of Seeds and Specimens
The plants here range from 2-year-old seedlings, recently set out from the sun pit to young trees that are head high. The smaller and more shallow rooted the plant, the less resistant it is to drought.
Yet this resistance is extremely variable with different plants. For instance, a 5-year-old specimen of Asiatic sweetleaf (Symplocos paniculata) might die more quickly than 2-year-old cotoneaster.
Birches: Most Susceptible To Drought
Of all the plants, the birches appear to be the most susceptible to drought, particularly the Asiatic species, though the native types are affected almost as much.
Our experience has shown that even in an ordinary season, a very young birch cannot withstand more than 2 or 3 weeks of drought without attention.
In addition, I have observed that in the most severe droughts, leaves of the native canoe birch (Betula papyrifera) have always been the first to turn yellow and fall, even on old trees.
Since the birch is so susceptible, you will probably wonder why it manages to reproduce itself so readily here in the northeast. The answer is one of nature’s oldest methods of survival, that of superiority in numbers.
Seeds of Birches
In their native habitat, birches seed themselves almost like grass, and out of the many that die, more than enough survive. Unfortunately, it is a method that the gardener cannot use.
Another susceptible group is the magnolias, both the Asiatic and the American species. Since our plants were given rather moist locations, we tended to ignore them at first, thinking the drought would not yet be felt there.
As a result, we lost a few valuable specimens. Though the ground had not thoroughly dried out, the sudden change from a very moist to a semiarid footing was enough to kill a plant not well Established.
Of all the shrubs, Asiatic sweetleaf has caused the most trouble. Newly transplanted specimens are apt to wither and shed their leaves in any ordinary dry spell, though they may recover under treatment.
However, in the severe drought of the summer of 1955, even older and well-established plants were constantly in danger.
Varieties of European Beeches
Beech, particularly varieties of the European beech (Fagus sylvatica), both the weeping and the tricolor, were somewhat troublesome if specimens were small and not well established. Deeper rooted plants seemed resistant.
Fortunately, two of the most commonly used groups on the home grounds, the oaks and many members of the rose family, proved very resistant.
I do not believe we lost a single oak. Even small, 2 and 3-year-old seedlings, almost lost in the grass and neither watered nor mulched, came through successfully.
Then, too, many members of the rose family, including apples, crab apples, peaches, cherries, spireas, lire-thorns, and cotoneasters, faired equally well.
We lost 2 crab apples out of perhaps 50, 1 plant of Prunus serrula, which had never been healthy, and a few seedling cotoneasters, which were neglected. It was a small loss compared with the great numbers which survived.
The maples are almost equally resistant, though a few of the smaller Asiatic varieties required watching.
Mulching of Older Plants
Older plants, mulched but not watered showed no damage. Of the deciduous shrubs, lilacs, buckthorns, brooms,, and the Russian olive suffered little.
The evergreens, of course, were a major problem. Since most of them come from temperate and fairly moist climates, they resent hot sun and dry winds and soil.
Most susceptible, the spruces and the firs, needed constant attention, even three and four feet high plants.
Young Evergreen
The difficult feature with a young evergreen is that it gives little sign when it is in danger, though an experienced person can tell something by the feel of the needles.
Even though young hemlock can appear green and flourishing one day, the next day it may start to shed its needles.
Once this happens, there is little hope for its survival. Larch and false-cypress or Chamaecyparis are almost as bad.
The pines, however, were much more resistant. Most of the young plants, both American and Asiatic, came through when given proper care.
They did need attention, but a few 20year-old specimens of red pine on dry knolls, left unattended, died.
Light Mulching and Watering
A light mulch and an occasional watering were all that was needed to protect even the youngest junipers and most of the cedars.
Both cedars of Lebanon and Atlantic cedars were entirely neglected and liked it. The drier, the more they seemed to flourish, and it was a joy to see them thriving while everything else seemed ready to give up.
Leaves Indicate Drought
The broad-leaved evergreens, of course, were always in danger. Fortunately, all of our rhododendrons and azaleas, and other acid-loving plants are set under pines, and so had the advantage of the shade.
Constant Watering and Heavy Mulching
With rhododendrons, it is easy to tell when they need water because their leaves curl. Constant watering, however, of the shrubs beneath the pines was necessary to keep them from drying out.
A heavy mulch around them helped to conserve moisture, too. The Asiatic hollies suffered, but they, like the hemlocks, did not indicate when they were in danger.
Shedding of Leaving of Japanese Holly
A young Japanese holly (Ilex crenata) could shed its leaves in a day without warning, but unlike hemlock, it might recover. Quick watering sometimes can save the plant.
The treatment that we find most successful is the result of six years of experience. The first year, caught unawares, the plants were left unmulched.
So, we resorted at once to daily watering, though it was unsuccessful. The hasty mulches, applied too thinly, resulted in heavy hisses of very small plants.
Growing in a Deep Grass
An important thing we learned was that a very small plant is safer if it is growing in deep grass than if the grass is trimmed away and a sparse mulch is applied.
The grass provides shade and keeps the soil from drying out as readily. Since the first summer, we have prepared for possible drought early in the season.
Heavy Mulching
In May, every plant is given a heavy mulch of freshly cut grass, with more added throughout the summer. At the first sign of drought, every small plant is given shade at once.
In that most of the plants have a circle of wire around them to discourage rabbits, shading is very simple. We merely scatter a few handfuls of grass or leafy branches over the tops of the wires, renewing these as they dry out.
If the plant is too tall, a hasty tepee of tall grass or branches is built around it. With this treatment, a light sprinkling every second or third day seems sufficient for everything, but the most susceptible species, resulting in less work and better results.
Severe Drought Can Kill Pines!
Our second season of the drought was by far the more severe, serious enough to kill a few 20-year-old pines.
Practically all fruit on full-grown shrubs, like viburnums and dogwoods, dried up and fell off, while leaves were burned black by the sun halfway to their centers. Yet, our losses of small plants were minor compared to the first summer.
Shade and mulch are, I believe, the most essential requirements. Without these, daily watering of small plants is almost valueless, because the ground dries hard an hour or so after the watering.
Depending on the Water Therapy
If we had to depend upon watering alone, I think the only system would be to put a quart metal can with a small hole in the bottom near the base of each plant.
Filled daily, the water would trickle out slowly enough to be absorbed by the plant before the sun evaporated it. Such a device might also be used for rare and susceptible specimens, along with the mulch and shade.
Under Field Conditions
In this article, I am referring only to plants grown under field conditions, which are given little if any cultivation.
Remember, therefore, that plants grown in nursery rows or in gardens, where the ground is kept loose and friable, might show different reactions. Daily watering in such soil might have a greater value.
Heavy Mulching: Most Effective Preservatives
We did find, however, that in the drought of the summer of 1955, a heavy mulch of lawn clippings and weeds, placed around perennials, like chrysanthemums, was one of the most effective preservatives.
Most plants will appreciate whatever shade they can get when the temperature hovers around the high nineties for a month.
When naturalizing any piece of land, with either native or exotic material, it is best to find out the average rainfall of the section.
Generally speaking, there is much local variation.
44659 by Fred Lape