With any plant, including fruit trees, water must move from the soil through the roots to the tree above the ground and into the air. This continuum is broken when trees are lifted in the nursery.
The shock that trees can get when they lose many of their roots in the nursery during lifting, and then are transplanted into a different soil environment, can lead to poor or no growth at all of new roots. This is called transplant shock and is often exacerbated when roots are not kept wet after lifting or when the trees are not supported and are allowed to rock and sway in the wind. Pear and cherry trees are particularly prone to transplant shock.
When the continuum is not quickly restored after the trees have been planted, the roots shrink due to loss of water by the aboveground part of the tree. As a result, trees cannot make new roots. Lack of active root growth of transplanted nursery trees means lack of cytokinin production. This in turn means that trees have difficulty leafing out, and production and transport of auxins to the roots is impaired.
When you plant your trees carefully and have established the continuum, roots may still not grow. Failure of roots to regenerate might also be caused by lack of oxygen because of waterlogged conditions and/or cold soil. Most fruit trees belong to the Rosaceae family which function best under a high soil oxygen level (higher than 10 percent). Root growth is suppressed within 30 minutes when oxygen levels drop below 5 percent.
When roots do not start to grow as a result of transplant shock or lack of oxygen, newly-planted trees will use their reserves of carbohydrates, nutrients, and hormones, and small leaves will appear. These leaves will then wilt and dry out, which can eventually lead to tree death. If your trees happen to survive this ordeal, you may save them by cutting the tops back in winter and start again. But you have lost the first (crucial) year.
To prevent or minimize transplant shock and give your trees a good start in life:
- Buy high quality trees with good root systems. Do not buy runts.
- Have the topsoil and the subsoil sampled and tested by a reputable laboratory for pH, phosphorus (P), zinc (Zn), manganese (Mn), sodium (Na), and chloride (Cl), and the need for gypsum.
- Prepare your soil well. Rototill the soil, making it crumbly. Apply lime, gypsum and/or superphosphate if necessary.
- Provide good drainage. Hill up the topsoil.
- Have a well designed irrigation system in place before you plant the trees.
- Have a support system (trellis) in place before you plant the trees.
- Soak the tree roots in water before you plant them.
- Cover your trees with a tarpaulin when you transport them to the block.
- Do not cut roots when you plant the trees. Roots store carbohydrates, nutrients and hormones. The cuts can become entrances for soilborne diseases. There is no gain in cutting roots except for ease of planting.
- When you plant, do not stomp the soil around the tree with your boots, as this compacts the soil and makes it difficult for water (and later fertilizer) to reach the roots.
- Cut feathers back to short stubs, do not head the trees.
- Always water the trees in, even after it has rained and the soil is wet. This will help attach fine root particles to the roots, restoring the continuum.
- ie the trees to the support system.
- Do not let the soil dry out around the roots, even when the trees have not yet leafed out. Put a few tensiometers next to some trees. Tensiometers will tell you if the soil is too wet.
- Do not mulch the trees. Mulch keeps the soil cold and wet in spring, which slows down root growth. Delay mulching until the trees have grown a little, or when the trees start to crop.
- Spray the trees to control diseases.
- Do not apply any nitrogen fertilizer until the new shoots are at least four inches long.
Van den Ende is a tree fruit consultant in Australia’s Goulburn Valley.