Plant or move plants in the fall to prevent shock

Last Updated: 
September 23, 2011

CORVALLIS, Ore. – Autumn is a good time to plant or move perennials, shrubs and trees in most places in Oregon. The wet and mild conditions can help prevent transplant shock and water stress.

"Shock is caused mainly by the demand of the plant for water and the limited ability of the root system to supply it," explained Ross Penhallegon, horticulturist with the OSU Extension Service. "The plant has a better chance of quick recovery if it has a chance in the fall and winter to develop new roots and build up nutrient reserves needed for healthy growth next spring."

If you dig and move a plant, try to leave as much of the root system as possible. In many urban areas, soils are compacted and sometimes poorly drained. You'll need to create a good root zone by amending the beds with sandy-loam topsoil and working the soil as deeply as possible.

Proper planting is the most important step. 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 critical. Trees often are planted too deeply 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.

Often in container-grown trees roots grow around the inside of the container. After you remove the container, gently straighten the roots. Otherwise, they can eventually girdle and kill the tree.

Fill the hole with soil about half full, lightly tamping it with your foot to remove air pockets. Make sure the tree stands upright. Water the plant slowly to saturate the soil and remove remaining air pockets, then finish filling the hole with soil. Remove extra soil rather than mounding it around the tree. You can build a temporary berm at the drip line to hold water around the root system.

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

Organic matter helps clay soil as well. The soil is easily compacted, which obstructs the movement of water and air. Mix in organic matter to help break up clay particles and improve water and air flow around the roots.

Contrary to popular belief, you don't need to fertilize trees when you plant them. In the spring, slow-release fertilizers are good for fall-planted perennials because their effect is long-lasting and less likely to burn roots than rapid-release products, Penhallegon said.

Newly planted trees require routine and thorough watering, particularly during Oregon's dry summer and fall months. Make sure the plant is well-watered for one to three weeks after transplanting. Add a layer of mulch around the base of the shrub to retain moisture and keep weeds from becoming established. Clean straw, clean manure, newspapers, a layer of black plastic or landscape cloth are all good mulching materials.

Water the tree regularly for at least three years after planting. If you have moved a shrub, it can help transplant shock to prune the shrub and make branches on top match the size of the root system.

Author: Judy Scott