1 - Fall planting of trees and shrubs is a good idea, but we can also plant container grown trees and shrubs in late summer.
Q. Everything I read says to plant trees in the fall when they are dormant. To plant a tree during the heat of the summer may stress it and cause it to die. I recently purchased several trees in buckets from a local nursery on clearance. Such a deal! My question is which is worse, to leave the tree in a bucket where it is already probably root bound for the next 3-4 mos. or attempt to transplant it at this time of year (Aug)? Don R. via University-wide Extension
A. You will often find recommendations to plant trees and shrubs in the autumn. There are several reasons for this. Nurseries often lower the price of plants to clear their inventory in preparation for the spring. As you mentioned, these plants have often become rootbound in the container and will only continue to do so if kept longer in the container in the nursery. There are also horticultural benefits from fall planting. Many trees grow a large proportion of their new roots in the autumn. At this time the air has begun to cool, reducing metabolic activity in the upper part of the plant, while the soil remains warm for several months. This results in greater metabolic activity in the roots in the autumn and greater root growth. Food material produced in the leaves in the summer is directed to the roots during this time because metabolic activity is greater in the roots. In New Mexico, we often have less wind in the fall, so staking of new plants is less critical while the roots are establishing. This results in less damage from staking materials and wind. Fall is a good time to plant, but your question about planting in August is relevant. In general, container grown plants may be planted anytime the soil can be worked (not frozen). Waiting a month or two may allow the roots to become somewhat more rootbound, but more importantly, it is difficult to maintain adequate moisture in containers than in the ground. So, for both reasons you can plant trees and shrubs in August. The only concern is that proper planting technique involves cutting the circling roots in the container. Cutting these roots results in a reduced root system to supply water to the top of the plant and wilting may occur. However, by mid-August temperatures are beginning to decline and, some years, the monsoon continues providing soil moisture and higher humidity to help plants cope with the reduced root system. This is the season when plants are programmed to produce new roots, so new root development should begin soon to replace those that were cut. Gardeners in parts of New Mexico where temperatures have remained extremely high may wish to delay a few more weeks, but that is not necessary. If you choose to delay, do so only if you can provide a shady place that is protected from the wind for these plants remaining in their containers. You must also commit to watering twice a day or more to sustain them in good condition until you can plant. You must provide these plants several months in the ground before the soil finally cools in order to establish new roots before winter begins. So, delay no longer than early September. Water the plants well when planting them. Apply organic mulch over the root zone and water every week at first. Be sure the plants have been well watered before the ground freezes in the winter. Specific information regarding planting trees and shrubs has been published in earlier Yard and Garden articles, so look for these articles at SWYG Archives.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.
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