Ornamental Plants

S. L. Emsweller, N. W. Stuart, and Curtis May.

The adaptation of ornamental trees, shrubs, bulbs, and flowering plants to a region is determined more by climatic conditions than by soil. Many varieties of such plants as camellias and azaleas can be grown only where the winters are mild.

Some herbaceous perennials, such as delphiniums, are satisfactory only in sections where cool summer temperatures prevail. Late-flowering varieties of such plants as chrysanthemums cannot be grown without protection in places where frosts come early.

One type of soil may be preferable to another for the growth of certain species of ornamentals, but there are no data regarding the best soil type for most ornamental plants. Recommendations are based almost entirely on observations of good growth in a particular type of soil, but plants of the same species often grow well in different types of soil.

ORNAMENTAL PLANTS often are planted in localities where the soil type is far from ideal. It is possible in most instances to replace or modify the physical characteristics and fertility of the soil for ornamentals. A deep, friable, well-drained, sandy loam that contains ample organic matter usually is considered suitable for most ornamentals, but some will thrive on soils less favorable.

Since some ornamental plants are known to grow well in the same general soil type we discuss such groups together in the paragraphs that follow. Information is usually available at State agricultural experiment stations as to what kinds of plants are best adapted in your climatic zone.

SHRUBS are widely grown throughout the United States for use in landscaping homes, gardens, streets, and parks. Their selection is usually governed by the color of flower, fruit, and foliage; time of blooming; ultimate size; and general availability. Environmental factors, such as temperature, light, water, and soil, however, determine the adaptability and amount of growth in a particular place.

THE NATURALLY occurring soil may limit growth because of poor structure and drainage, lack of essential nutrients, or unfavorable soil reaction. Many shrubs will tolerate or even thrive on a wide range of soils, but others are more exacting, particularly as to soil reaction.

Azaleas, as typical of this group of plants, grow best at pH 4.5 to 5.5 in well-drained sandy loam that contains a plentiful quantity of organic matter, including partly rotted oak leaves,twigs, bog peat, and old sawdust. Soil structure is most important and must permit ample aeration in the root area and high water-holding capacity. (Some shrubs, such as juniper and bayberry, require an acid soil but tolerate dry sites.) A mulch of peat moss or oak leaves maintained throughout the year at a depth of 2 to 3 inches tends to control soil reaction, provide some nutrients, and maintain iron availability. The main nutrient required is nitrogen, which can be supplied in organic form from cottonseed and soybean meal or as ammonium sulfate.

CHLOROSIS a yellowing of azalea leaves, which results from iron deficiency caused by root injury, lack of acidity, use of excessive amounts of lime and phosphorus, poor drainage, and certain nutrient deficiencies, can be corrected temporarily by spraying the plants with ferrous sulfate or by applying chelated iron to the soil. These treatments cannot substitute for good soil and growing conditions, however.

Certain shrubs, such as the barberry, daphne, and lilac, grow well under neutral or slightly alkaline conditions sometimes found in the humid regions. They and many other species will grow in slightly acid soils, however. Their growth is generally influenced more by light, fertility level, and water than by soil reaction.

SHADE AND ORNAMENTAL TREES, within their climatic limitations, in most instances grow best on a fertile, well-drained loam, but they will tolerate a wide variety of soil conditions.

A poor internal soil drainage, with resulting poor aeration, is detrimental to the growth of most species of trees, but some kinds will grow on wet sites.

Poor soils unsuited for satisfactory growth of shade trees usually may be modified by the addition of sand, peat, or decayed leaves or by installing drains, so that good growth can be obtained.

Before selecting shade trees, you will do well to consult your State agricultural experiment station, or other local authorities, about the kinds best suited for your locality.

In the following list we give examples of kinds of trees that require special types of soil for good growth or that will grow in certain types of soils:

Trees that need an acid soil:

Pin Oak (Quercus palustris); becomes chlorotic on neutral or alkaline soil.

Strawberry-tree (Arbutus unedo).

Trees that will grow on relatively dry soils:

Velvet Ash (Fraxinus velutina).

Acacia (most species).

Tree-of-Heaven (Ailanthus altissima).

Boxelder (Acer negundo).

Chinaberry (Melia azedarach).

Smooth Arizona Cypress (Cupressus arizonica bonita).

Carob (Ceratona siliqua).

Giant Evergreen Chinquapin (Castanopsis chrysophylla).

California Peppertree (Schinus molle).

Eucalyptus (most species).

Green Ash (Fraxinus pennsylvanica lanceolata).

Hop Hornbeam (Ostrya virginiana) Pignut Hickory (Carya glabra).

American Hornbeam (Carpinus caroliniana).

Eastern Redcedar (Juniperus virginiana).

Jujube (Zizyphus jujube).

Pacific Madrone (Arbutus menziesi).

Mimosa (Albizzia julibrissin).

Chestnut Oak (Quercus montana).

Oregon White Oak (Quercus garryana).

White Poplar (Populus alba).

Fremont Cottonwood (Populus fremonti).

Jerusalem-thorn (Parkinsonia a aculeata).

Blue Paloverde (Cercidium floridum).

Ponderosa Pine (Pinus ponderosa).

Brazil Peppertree, Christmas-berry Tree (Schinus terebinthifolius).

Torrey Pine (Pinus torreyana).

Virginia Pine, Scrub Pine (Pinus virginiana).

Pitch Pine (Pinus rigida).

Russian Olive (Elaeagnus angustifolia).

Sassafras (Sassafras albidum officinale).

Trees that will grow on wet soils:

Alders (several species).

Baldcypress (Taxodium distichum).

Cajeput Tree (Melaleuca leucadendron).

Dahoon (Ilex cassine).

Eastern Larch, or Tamarack (Larix laricina).

Poplars (Populus) most species will grow on wet soils.

Whitecedar Falsecypress (Chamaecyparis thyoides).

Red Maple (Acer rubrum).

Pin Oak (Quercus palustris).

Water-elm (Planers aquatics).

Sweetbay Magnolia (Magnolia virginiana).

American Sweetgum (Liquidambar styraciflua).

Willow (Salix) (most species).