Fall is Good Time to Plant or Move and Replant Perennials, Shrubs or Trees

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Last Updated: 
November 5, 2010

CORVALLIS, Ore. – Do you have a small tree or shrub you want to move? Or have a space you'd like to fill in with a new perennial, shrub or tree?

Mid-autumn is a good time to plant or move and replant landscape plants in most places in Oregon. The wet and mild conditions of October may help prevent transplant shock.

When shrubs are brought home and transplanted, they may suffer varying degrees of shock. This may be from root loss (for field-grown plants) or the changes in care practices (for container-grown plants). Weather conditions and the condition of your soil can also have an impact on how well and quickly a plant adjusts to its new location.

"The shock is mostly caused by the demand of the plant tops for water and the limited ability of the root system to supply it," explained Ross Penhallegon, horticulturist with the OSU Extension Service. "A plant's demand for water is less in cool and rainy fall weather, and the plant has a better chance of quick recovery, especially if it has a chance to develop new roots before the next growing season."

Fall planting also gives the new plant time to establish the necessary root growth required to anchor it in the soil and time to build up nutrient reserves needed for healthy growth next spring.

Locally grown nursery stock is available in most nursery and garden stores and many varieties of transplants are available. Penhallegon advises buying nursery plants grown in Oregon and adapted to local climates and soils.

If you are digging up and moving a plant from one location to another, try to leave as much of the plant roots as possible.

In many urban areas, gardeners will find that the soils are compacted and sometimes poorly drained. In these situations, you'll need to create a good root zone by amending the beds with sandy-loam topsoil and working up the soil as deeply as possible.

Proper planting is the most important step. Many problems with a tree or shrub can be traced back to improper planting. Dig the hole at least two feet wider than the size of the root system or root ball. A large hole will allow better root growth and is especially important in compacted soils. Roughen the sides of the hole, which should be the same width at the top and bottom, and remove any rocks or debris.

Planting depth is of critical importance. Trees often are planted too deep in the hole. Carefully set the tree in the hole at the same depth or slightly higher than it was at the nursery or in your yard. Plant it with the root collar at ground level or slightly higher (two inches) to allow for settling. If you replant at the exact ground level, eventual settling will put the growing crown below the level of the soil, allowing it to sucker.

With balled and burlapped trees, support the root ball with your hands and gently place the tree in the hole to test for proper depth. Never drop the tree on the ground or in the hole as this disturbs the root ball and can break the roots.

Container-grown trees often have roots growing around the inside of the container. After removing the container, gently straighten the roots. If they are not straightened they will eventually girdle the tree.

If you plan on staking your tree, drive two wooden or metal posts along the sides of the hole before you backfill. This prevents you from accidentally driving the stakes through the root ball and damaging the root system.

Fill the hole with soil about one-half full, lightly tamping it with your foot to remove any air pockets. Make sure the tree is standing upright and not leaning. Water the plant slowly to saturate the soil and remove any remaining air pockets, then finish filling the hole with soil. Remove any extra soil rather than mounding it around the tree. Build a temporary berm at the drip line to hold water around the root system.

Amendments are additions to the soil that enhance its moisture-holding capacity, nutrient availability, or structure. Amendments include good loamy topsoil, peat moss, and various kinds of mulches. Most soils in Oregon – except sandy soil, soil with high clay content, or soil that has been heavily disturbed by construction – don't require amendments.

Sandy soil, often found in eastern Oregon or along the Oregon coast, benefits from the addition of organic matter such as peat moss, compost or old sawdust to the planting hole to increase the soil's moisture-holding capacity around the roots.

Additions of organic matter also help clay soil. This soil is easily compacted which obstructs the movement of water and air. Mixing in organic matter helps break up clay particles and improves water and air flow around the roots.

Generally, the OSU Extension service recommends a ratio of one-third amendment mixed with two-thirds of existing soil for backfill. Use caution with non-composted animal manure, which may be hot from biological activity or high in salts.

Contrary to popular belief, you don't need to fertilize trees when you plant them. Fertilizing with nitrogen in the fall may contribute to cold damage transplant shock. Never use lawn fertilizers in a planting hole. However, potassium and phosphorus may help the roots to establish.

Slow-release fertilizers are good to use in the spring on fall-planted perennials, as they have a long lasting effect and are less likely to burn the roots than rapid release products, said Penhallegon.

Newly planted trees require routine and thorough watering, particularly during Oregon's dry summer and fall months. Water the tree regularly for at least three years after planting. If you have moved a shrub, it might help the transplant shock to prune the shrub to make the branches and foliage on top match the size of the root system.

Make sure the plant is well watered for one to three weeks after transplanting. Adding a layer of mulch around the base of the shrub will help prevent weeds from becoming established and help soil to retain moisture. Clean straw, clean manure, newspapers or a layer of black plastic are all good mulching materials.

Author: Carol Savonen
Source: Ross Penhallegon