Young apricot trees are likely to make excessive growth, especially trees from 2 to 5 years of age. Trees making excessive growth do not mature early in the fall and are, therefore, more subject to injury from low temperatures in November and early winter. Mature apricot trees are hardier than young trees.
Trees should not make more than 2 feet of annual growth.
It is extremely important to train young trees correctly to prevent weak crotches that are very susceptible to winter injury.
The southwest side of the trunk can become very warm on sunny days in late fall and winter. Night temperature frequently drops to well below freezing. This alternative freezing and thawing often injures the bark and wood. This permits wood-destroying fungi to gain entrance, and a large canker is likely to develop.
Paint the trunk with a latex-based, white paint. This paint is non-caustic because it is fast-drying and does not contain turpentine or oil. It gives good coverage throughout the winter, and the white surface reflects the sun's rays, preventing deep bark penetration. Brush the paint onto the trunk from the ground line up to the first scaffold branch. CAUTION: Do not use ordinary house paints containing oil, turpentine or lead. These may seriously injure or kill the trees.
Fill any holes that develop in the soil at the base of the trunk. Make certain that the soil level adjacent to the trunk is slightly higher so that water will drain away from the tree. Water collecting in depressions near the trunk will form ice in late fall or winter. This ice may girdle the tree, causing death or serious injury.
Do not use apricot trees grafted on peach seedlings. Manchurian apricot seedlings and seedlings of the Michigan apricot selection, Goldcot, are compatible with apricot varieties. The Manchurian seedlings are especially winter hardy and have given strong, healthy trees with minimum tree loss.
The standard varieties produced in the West have failed in Michigan. Goldcot is the primary variety grown in Michigan. The cultivars listed are reported to be hardy in the north.
Goldcot - The most dependable variety for planting in Michigan. Early Golden Hardy Iowa - Good for fresh fruit or cooking. Moongold - Must be planted with Sungold for pollination. Fruit suitable for most uses. Sungold - Must be planted with Moongold. Good fresh or in preserves.
The Use of Pollinators
Goldcot is apparently completely self-fruitful and can be planted alone. The other varieties, while ordinarily self- fruitful, will set heavier crops when unfavorable weather prevails during blossoming periods if they are inter-planted with other fertile varieties.
Site and Soil
Apricot trees are sensitive to climatic conditions and require the best possible growing sites to remain healthy and regularly productive. Some favorable Michigan sites for apricots exist in the northwestern area (Leelanau county) of Michigan. Apricots seem to grow and produce well in locations where sweet cherries are productive.
Apricots blossom about a week earlier than peaches. Therefore, plant apricots only on sites which are practically frost-free. Elevation of the site above the surrounding country will give added protection against loss from frost and winter injury. Nearness to a large body of water is associated with slow warming temperatures in the spring, which help hold back spring bud development.
The soil must be well drained and preferably of a sandy type. Poor subsoils of any kind will result in the death or poor growth of many trees. Avoid heavy soils for apricots as such soils are likely to be poorly drained.
Fall-planted trees are more subject to cold injury during the first winter after planting. Plant the bud union 4 inches below ground level for good anchorage. The soil should be well settled and firm around the roots.
Training and Pruning
Train the young tree to the modified central- leader system. Select two main scaffolds on opposite sides of the trunk, well separated so they will not touch each other when fully grown. The first scaffold should be about 30 inches above the ground if trees are to be mechanically harvested. The second scaffold should be 8 to 10 inches above the first. Select scaffolds having wide angles at the point of attachment with the trunk. Sharp-angled branches split badly. The leader must be left longer than the scaffolds so that it will not be shaded out.
It is very important the second spring to remove all excess scaffolds from the trunk, retaining just two or three. Head the scaffolds back somewhat if they are likely to grow higher than the leader.
By the third and fourth years, the trees are beginning to produce some fruit. The main framework of the tree has been established, and pruning is mostly to remove additional branches that may come from the trunk, and to head back new terminal growth if it exceeds 2 feet in length. A small amount of thinning out may be necessary where branches are too thick or are rubbing. Do not leave too many branches originating close together on the trunk.
Pruning the Mature Tree
The apricot produces most of its fruit on rather short- lived spurs. Prune mature trees to remove branches loaded with old spurs and keep the trees producing good replacement wood. This requires a combination of thinning out branches having many weak spurs and heading back long branches by one-third or to a strong lateral branch. Mature trees must make from 16 to 24 inches of new terminal growth a year to maintain satisfactory annual production. If less growth is made, the trees will fall into a biennial bearing habit and produce a large crop of small apricots every other year. Prune or head back the long branches in April. Additional pruning in June and August will reduce excess vigor. Do not prune during late fall or mid-winter because of drying out and the possibility of winter injury.
Grow young apricot trees slowly. They have a tendency to make excessive growth, rendering them more susceptible to winter injury. New growth should not exceed 2 feet in length annually.
Nitrogen is the most important nutrient in fruit production and is usually the only fertilizer element that should be applied regularly in Michigan. However, young apricot trees have great inherent vigor even on relatively poor soils; therefore, nitrogen fertilizers should not be used in young plantings on reasonably fertile land and sparingly even on light, sandy soils. As the trees become older, start producing and the danger of winter injury becomes less, nitrogen applications will need to be increased sufficiently to insure an annual terminal growth of 16 to 24 inches to maintain good production. Apply nitrogen in late fall, after mid-November, or before growth starts in spring. The kind of nitrogen to use should be chosen on the basis of cost of actual nitrogen and ease of application; however, nitrogen in the form of urea should be avoided.
Potassium is the only nutrient element, other than nitrogen, that is likely to be needed in Michigan apricot plantings. Potassium deficiency reduces tree growth, yields and fruit quality. The best way to determine need for potassium (potash) is through leaf analysis. When needed, potash may be applied in the fall or spring. The most common potassium fertilizer is muriate of potash (60 percent K2O).
Phosphorus is utilized in only small amounts by fruit trees compared to either nitrogen or potassium. There is no present indication that apricot trees will benefit from application of phosphorus. However, in some cases, fertilizers containing phosphorus may benefit growth of cover crop.
If fruit set is heavy, thin the individual fruits so that they will be 1 1/2 to 2 inches apart. Otherwise, fruits will be small, and the trees will become biennial in bearing habit. Thinning can be done by hand, or -- faster and easier -- by careful pole thinning. Bamboo poles of various lengths are used. Cover the top 12 inches with a piece of garden house to reduce injury to the branches. The excess fruits may be removed by rubbing and tapping. Avoid hard blows, as all of the fruits will be knocked off for a considerable distance from the point of contact. Early thinning is recommended. Start thinning as soon as danger of frost has passed.