view counter

Secrets of Successful Transplants

Getting to the roots of woody plants

Did you know that when the stems of an oak tree are growing in the spring, the roots are not growing? Conversely, when the top of the plant has stopped growing and has stopped producing new leaves, the roots initiate growth. It’s the same with most woody plants. Most are unable to grow at both ends at the same time.
    In the spring, the stems and leaves are elongating and unfolding, while the roots are busy providing them water and nutrients. At maturity, the full-sized leaves begin sending down compounds such as carbohydrates, hormones and other metabolites used by the roots to produce new roots. In some plants, this cycle repeats itself. Many deciduous species will produce two or more flushes of top growth with brief periods of root growth. In other plants such as pine trees, there is usually only one flush of growth.
    Plants need to grow new roots because nutrients are absorbed only at the tips of roots. Nearly all nutrients are absorbed by root hairs, and these only occur on newly formed roots. As soon as new roots begin to form, the root hairs deteriorate, and that part of the root is covered with suberin, a sugar-like substance that enables the root to absorb only water.
    In other words, most of the roots of plants function as pipes, carrying nutrients and water to the stem when the tops are growing, then carrying metabolites to their own tips when roots are growing.
    This is knowledge you need to transplant trees and shrubs successfully. To assure better survival, growers root-prune plants a year or two before transplanting. To root-prune, make a circle of deep cuts at the plant’s drip line, severing the roots with a sharp spade.
    Wait until after woody plants have stopped producing new leaves in the first flush of growth. Root pruning during shoot elongation and leaf growth often results in severe wilting and loss of foliage, thus weakening the plant. Late-summer root-pruning has another advantage. More buds have formed, resulting in the maximum production of natural hormones that stimulate new roots.
    Annual plants are another story. In annuals, tops and roots grow simultaneously. This is possible because these plants have the advantage of growing only during long days and warm weather.
    Understanding root growth also helps you care for potted plants. Plants grown in containers have limited space for root growth. Keeping the plants in the same container for too long results in root-bound plants. There is no more room for roots to grow. Root-bound plants deteriorate or may flower profusely, wilt frequently and stop growing. Those are signs that it’s time to repot. When repotting, slash or tear apart the root ball to stimulate new roots to grow.