After Planting Care of Container Grown Plants
James E. Cross, Cutchogue, New York
Reprinted from New York Chapter Newsletter
Plants which have been grown in containers require direct and careful irrigation after they have been planted and until they become well established in the surrounding soil. The care required is in addition to that normally given all new transplants. Plants which are dug from the ground have many of their roots cut, thereby initiating root growth which hastens their eventual reestablishment. The container grown plant's roots are not disturbed by the removal of the container before planting and it has no immediate incentive to send roots into the surrounding soil. Most fatalities of container grown plants result from the plant drying out and this can happen even when the surrounding soil is still quite moist.
The critical period of time until the plant becomes established will vary according to soil conditions (the slowest is from light porous container growing medium into heavy sticky soil, next is heavy container medium into light soil). The amount of extra water required will vary with the type of plant (fine shallow rooted plants require greater frequency) and the stage of growth (more frequent where there is soft, new growth and/or flowers to support) and of course, the type of soil (more frequent for sandy soils). To be safe in average soils with good bottom drainage provide 1 inch of water at least once each week throughout the first summer. A good heavy mulch will help hold moisture.
Steps should be taken to shorten the critical establishment time. First prepare carefully a large (several times size of existing root ball) planting hole. This is to provide a zone around the plant for easier transition of the roots into their new home. Remove ¼ to ½ of the soil and replace by thoroughly incorporating materials which give more friability to the soil. The more extreme the existing soil conditions (heavy clay or light sand) the more supplementary materials need be added. Sand and perlite type materials are excellent for light, sandy soils. In using peat, it is important to mix it very well with the soil. Make certain also to dig very deep to eliminate any drainage faults which will lie beneath your plant. Almost all plants need good drainage.
The next step is to loosen or cut some of the roots before planting. By extending some of the roots out into the planting hole you begin to break the former root habits. For fine rooted plants, gently loosening the outside layer of roots should be sufficient. When roots are coarse, loosen them or cut them with a sharp knife or pruners - particularly if they are severely coiled on the sides or bottom. Bad kinks and coils should be eliminated. If a lot of roots need to be cut away in the process, offset by pruning back or thinning out the top of the plant. While undertaking these steps, do not allow the roots to dry. When backfilling the hole, create a circular ridge or dam to form a water basin located so water that collects will go directly into the root ball rather than into the surrounding prepared soil.
Where container grown plants are planted in late summer or fall, assume that they will go into the winter without being thoroughly established. Provide some winter protection (sun and wind break) to the foliage.