PLANTING FOR SUSTAINABLE LANDSCAPES


INTRODUCTION

Giving plants a healthy start begins with proper planting. Problems showing up on established plants more often than not can be traced back to poor planting. Traditional ways of planting are often passed down through generations of landscapers. While some of the old ways are still recommended today, many planting practices are changing to reflect current research and technology. Well-informed landscapers and arborists should be aware of the latest planting and transplanting techniques. The objective of this chapter is to have you learn the techniques and procedures used to plant and transplant trees and shrubs, and to have you understand how the use of proper planting techniques can improve survival and accelerate establishment.


SELECTING AND PURCHASING PLANTS

The Right Plant
A key to sustainable planting is matching the plant and the conditions of the planting site. The best planting procedures known will not save a plant that is poorly suited for it's site. Plants naturally vary in their ability to tolerate site conditions such as extreme heat or cold, wet or dry soils, sun or shade. The plant also should not outgrow it's allotted space. Plants should be healthy and vigorous when planted. The condition of the roots in particular affects transplant success. The roots should be white and numerous; brown or black roots indicate a health problem.

Handling New Plants
Trees and shrubs are available from the nursery in one of three forms; bare root, balled and burlapped or container-grown. Depending upon site requirements and planting specifications, each form has its advantages and disadvantages.

Bare root plants have had the soil shaken from their roots after digging. Most bare trees and shrubs plants are purchased by mail order and planted during the dormant season, before roots and buds begin to grow. Since there is no soil on the roots, it is vital that they be kept moist, and if not planted immediately, that they be stored cold (32° - 40°F), with moist packing around the roots. When planted, the roots of bare root plants should be spread evenly in the planting hole.

Container-grown plants have been grown for months or years in the container in which they are sold. Container-growing is becoming very popular in the nursery trade. Container-grown plants may be planted anytime the soil is workable, but may need special attention to correct compacted or circling roots. When selecting container-grown trees and shrubs, always check the roots. For example, not all plants purchased in containers are container-grown. Often bare root trees or shrubs are potted in containers, grown on for a short time and sold from the nursery. If they are not held for at least a year, the roots may not have established in the container. On the other hand, if plants are grown in their container for too long, the roots may have grown in circles. These roots must be separated and spread out during planting. If the roots are densely matted, the outside of the root mass should be sliced vertically with a sharp knife in a few places to help separate the roots. And unless the container is biodegradable, such as a natural peat pot, it must be removed before planting.

If properly watered and maintained, container-grown trees can be planted any time of the year. Early fall planting is especially advantageous because the roots can begin to establish before the plant goes dormant for winter. Early spring, before bud break, is also a good time to plant because the roots begin to grow immediately, and light, temperature and soil moisture levels are optimal. Perhaps the most important factor in successfully transplanting container-grown trees is maintaining adequate soil moisture, which encourages roots to grow into the surrounding soil.

Many trees and shrubs are dug in the nursery with root balls intact, and wrapped with burlap. Be aware that as much as 95% of the absorbing roots can be lost in digging, though some roots are preserved in the root ball. When selecting a balled and burlapped plant be sure the ball is solid, with little or no movement of the trunk. The burlap used to wrap the root ball holds the soil ball together and keeps the roots from drying out. Natural fiber burlap is biodegradable, and may be left in the hole, though it should be rolled back and completely covered with soil. Some nurseries use treated burlap or synthetic burlap, this should be removed at planting. All twine or rope holding the burlap together or tied around the trunk must be removed to avoid girdling. Some larger balled and burlapped trees come in wire baskets that keep the ball together during handling. Although the baskets do not have to be removed, it is best to cut the upper rows when planting. This eliminates interference with rakes or lawn mowers if the tree is planted shallow, and allows roots to grow and spread freely near the surface.


PLANTING

The Planting Hole
Installing trees and shrubs properly involves more than just digging holes and setting in plants. The quality of the planting hole will determine the long term health of the root system, and thereby the entire plant. In general, the planting hole should be at least 18 to 24 inches wider in diameter than the root ball. If the soil is compacted, or of poor quality, the hole should be even larger - 3 to 5 times the width of the root ball. The hole should be wider at the top than the bottom, with sloped walls, because most of the root growth will be shallow and horizontal. Planting too deeply can stress the plant and drown or suffocate the roots. The easiest way to avoid this is never to dig the hole deeper than the root ball. Soft fill should not be left in the bottom of the hole, as the root ball will settle and be planted too deep. In almost all types of soil, the tree should be planted slightly shallow, with the top 2 - 4 inches of the root ball sitting above the surrounding soil grade. Remember, the exposed portion of the root ball will be covered with 2 - 3 inches of mulch by the time you are finished planting.

Drainage is also an important consideration in successful planting. Poor drainage kills more plants than any other cause. A poorly prepared planting hole may act as a dish and hold water, especially in clay soils. Oxygen levels are low in the bottom of such holes, and not conducive to healthy root growth. Do not put gravel in the bottom of the planting hole; it does not aid drainage.

The Root Ball
Handle roots carefully during planting - small absorbing roots are easily broken. Check balled and burlapped plants to ensure the roots originate near the surface of the ball. When setting the plant in the hole, make sure these roots are no deeper than the soil grade.

Backfilling
In most cases it is best to backfill the hole with the same soil that came out of the hole. Research has shown that soil amendments do not improve plant establishment or growth. However, if the natural soil is extremely poor, topsoil may be the only alternative. Strive to match the backfill soil type to the soil type of the site, as closely as possible. Backfilling with a sandy loam in heavy clay soils may cause the planting hole to collect water and suffocate the roots. If soil must be brought to the site, or the backfill must be amended, the hole should be extra wide. This will allow for several years growth within the new soil. While backfilling, work the soil around the ball so that no air pockets remain. Large pockets of air can allow roots to dry out. Firm the soil so that the plant is vertical and adequately supported, but do not pack the soil. Water thoroughly while backfilling. The remaining soil should be mounded into a berm, on the outer edge of the hole, to collect water over the root zone, especially on sloped sites. Remove all tags or labels so that they will not girdle the trunk or branches as the plant grows.

Mulching
After filling the planting basin with water and letting it drain, fill the basin with 2 to 3 inches of an organic mulch. This will conserve soil moisture, moderate soil temperature extremes and reduce competition from weeds and turf. Many organic mulches, such as pine needles, bark or wood chips, are fine. Make certain the mulch is not touching the plant stem, as this could promote bark decay, crown rot, winter injury or rodent damage. Do not use black plastic or landscape fabric under the mulch, since these materials, sooner or later, restrict water movement and oxygen availability to the roots.

Water and Fertilizer
Planting is a major operation from which most trees and shrubs recover slowly. A major portion of the root system is lost in digging, and the plant must reestablish sufficient roots to sustain itself. In this time, the plant's ability to obtain and transport water and minerals is greatly reduced. The result are varying degrees of water stress and transplant shock. For this reason, proper watering is a key to the survival of newly planted trees and shrubs. If rainfall is not sufficient (generally 1 inch/week), the tree should be watered every five to seven days. A slow gentle soaking of the root zone is preferable. Your watering patterns should be appropriate for the soil type and drainage - remember that excess water in the planting hole is a leading cause of transplant death.

Since the root system functions of a newly planted tree are limited, fertilization often is not recommended at the time of planting. Excessive fertilizer in the root zone can be damaging, so do not add fertilizer to the backfill. If fertilizer must be used at planting or in the first growing season, apply a controlled-release fertilizer or liquid feed. Fertilizing in the fall, when the roots are active, can be beneficial. However, most plants received from the nursery require no fertilizer in the first year of establishment.

Pruning
Plants grow and establish fastest if pruning is minimized at planting. Beyond the removal of broken or damaged branches, it is usually best to avoid heavy pruning.

Staking and Guying
Most shrubs do not need to be supported after planting. In general, trees under 8 feet in height do not need support either. In fact, staking can have detrimental effects on the development of trunk taper and root growth. Too often, staking materials end up injuring or girdling the tree.

Trees may be supported by up to three stakes. If a single stake is used, it should be placed on the upwind side of the tree. The material used to attach the tree to the stake should be broad, smooth and somewhat elastic. The tree may be attached to the stake at several points along the trunk. However, do not stake the tree too rigidly, as the tree will develop a less sturdy root system and be more subject to girdling. If two support stakes are used, a single, flexible tie attached to the tops of the stakes will be sufficient. Triple staking provides more protection against strong wind and lawn mowers. Support stakes and guy wires generally should be removed after one growing season. If staking is left in place for more than two years the tree's ability to stand alone may be reduced, and the chances of girdling injury are increased.
Based on information found in the International Society for Arboriculture Arborist's Certification Study Guide, the Penn State University Master Gardener Manual, and Arboriculture: Integrated Management of Landscape Trees, Shrubs, and Vines, by Richard W. Harris.


This page maintained by BRIAN K. MAYNARD
E-mail: maynard@uriacc.uri.edu