By Steven Cramer, Horticulture Agent, Colorado State University Cooperative Extension
How can the homeowner keep shrubs and trees healthy during the spring and throughout the year?
For an answer to this question, it's important to know something about the needs of healthy plants. Facts to consider include a plant's capacity to make and store carbohydrates, enough soil moisture, and soil that has adequate nutrients and is conducive to plant growth.
Capacity to make and store nutrients: This is important to all plants and it is not as simple as it may seem. Each perennial plant must be able to store adequate carbohydrates, not only to reproduce leaves for each year, but also to "hold in escrow" the energy needed to grow new leaves, if they are killed by frost or destroyed by wind or hail.
If graphed, the carbohydrate storage curve would be high in early spring, just before trees leaf out. After leaf-out, it would plunge (because the tree has used a lot of stored food energy to put on new leaves). Then, in midsummer or later, the curve would rise again, as the tree begins to build new food stores.
Trees and shrubs use stored nutrients in early spring. By the end of spring, after a tremendous growth spurt, trees have used up a lot of these nutrients. A healthy tree will begin, through the process of photosynthesis, making new supplies of nutrients (carbohydrates).
Though summer is hot, the healthy plant will continue to make and store nutrients sufficient to carry it through the winter. In fall, plants begin to lose their leaves and go dormant for winter, and the tree's food-making capacities slow down.
By knowing this cycle, it becomes apparent that the plant must be healthy enough to manufacture, store and use adequate nutrients throughout the year. If it isn't, you will end up with dead branches or even a dead tree. In some cases, a tree may have just enough food stored to begin leafing out, but not enough to continue growing. In that case, the tree will die. Proper plant care, year-round, should prevent this from happening.
Soil moisture: Too little or too much moisture will result in a tree dying back or dying off. As a rule of thumb, soil needs to be moist to between 12 to 18 inches of depth for most trees and shrubs. The only way to check moisture depth is to check by careful digging or by using a soil probe after watering the root area.
Don't assume you are watering a tree when you are watering your lawn. Most of the water may go to the lawn, which has many roots competing with tree roots. Thatch in the lawn acts to repel water, and different soil types make water penetration very difficult in many cases. Soaker hoses and root waterers can be useful tools for applying water.
Be sure to apply water during extended winter dry periods. This is vital to good tree health.
Soil types: Soils can vary greatly within a short distance. Generally, Front Range soils tend to be clayey and alkaline. However pockets of sandy soils can be found in some areas. You need to ascertain what type of soil you have and take steps, gradually, to improve it. If yours is a clay soil, aeration will help provide oxygen needed for optimum plant health.
Soil nutrients: In general, trees do not need as much fertilizer as do lawns. However, in our generally high pH soils, nutrients, such as nitrogen, iron, zinc and manganese, can be added. Note the color of leaves and needles. If they look sickly or light colored, that is a clue that additional nutrients may be in order. If you are concerned about soil health, you might consider having your soil tested.
By understanding these and other plant needs, you will know how to provide healthy plant care, not only each spring, but throughout the year.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010