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Soil Chemical Properties

Program Contact: Tianna DuPont, Tree Fruit Extension Specialist
(509) 663-8181 •


There are many potential chemical imbalances that must be addressed prior to planting. The pH of the orchard soil is probably the most common problem. Orchard performance will be improved if the soil pH is between 6.2 and 7.2. If pH is lower than that, an application of agricultural lime is required. The best time to apply this product is while you can still identify the old tree rows. The pH is lowest under the trees, and that is where most of the lime should be spread. When the soil is ripped and disced prior to planting, the lime will mix with the low pH soil, react with the acid, and rapidly improve the pH. If your soil is low in magnesium (by test) dolomitic lime should be used. This is the least expensive way to add magnesium, a major nutrient, back into your orchard system.

(More lime information)

If your soil test suggests a general problem with low nutrient levels, such as phosphorus and potassium, this pre-discing period is the most effective time to apply appropriate rates. If soil P and K are already adequate, adding these fertilizers is not likely to help. Zinc fertilizer, broadcast or banded, and mixed with the soil before planting, will greatly improve the zinc nutrition of young trees for the first two or three years after planting. Boron applied in the preplant application will help for the first season. Foliar zinc and boron can be applied at low rates two or three times during the growing season during the first two years, then applied as you would to a mature tree from the third season onwards.

Arsenic and lead residues, left over from efforts to control codling moth in the 1930’s through about 1948, have been blamed for much of the tree growth restriction on old orchard sites. In many cases, arsenic in a replanted site is an excuse for poor growth, rather than a true cause. These residues can slow tree root growth, adding to the problem if other factors are not addressed properly, but trees can tolerate much higher levels than were once considered toxic.

replantqThe picture on the right is of a Gala/M7 after its first growing season, planted in an orchard with a serious replant disease problem and an soil arsenic level of over 200 ppm. As you can see, the tree is doing fine.

Many apple or pear orchards have shown almost no effect when the preplant soil arsenic test showed levels below about 150 parts per million. If your soil test shows levels near this level or higher, your apple or pear trees will probably grow better if you plant them individually, with at least the equivalent of two or three 5-gallon buckets full of “new” soil around the new tree roots.

There are some rare sites where arsenic levels are over about 200 ppm. Levels this high or higher may cause tree growth restriction unless a large amount of new soil is placed around replanted tree roots. It is too expensive to replace the amount of soil necessary to ensure good long-term tree growth in these few sites.

Stone fruits, especially peach, nectarine, plum and apricot, are quite sensitive to above-normal levels of arsenic in the soil. These fruits will often defoliate in the late summer if planted on arsenic levels of over 75-100 ppm. In the “stone fruit” group, Cherries are the most tolerant to soil arsenic, but less so than apples and pears. There is also quite a wide variation in tollerance to soil arsenic amongst the stone fruit varieties. For instance, “Lapins” cherry seems more sensitive than “Bing”.