Before fertilizing trees, have your soil tested

When diagnosing a tree’s health problems, inevitably the question arises about fertilization. Trees require certain mineral elements for healthy growth. Nutrient deficiencies can cause a reduction in shoot growth, leaf size, foliage to fade, and distort – sometimes in a characteristic pattern that helps identify the cause. Severely deficient trees produce fewer leaves, exhibit dieback and are predisposed to other maladies.

Generally, there are sufficient macronutrients (nitrogen, phosphorus and potassium) as well as micronutrients (iron, manganese and zinc) present in landscape soils. Additionally, trees located in a lawn utilize the nutrients from fertilizers applied to the turf. If you reduced the turf in your yard and installed plant material with an organic mulch, soil fertility is usually increased by nutrients from the mulch decomposition.

The physical properties of soil (texture, depth, and structure) influence the amount of nutrients that the soil holds and, to a certain extent, the availability of nutrients to the tree. Most nutrient deficiency symptoms are caused by adverse soil conditions such as high soil pH, inappropriate irrigation, poor drainage, physical injury to roots and root decay pathogens.

Soil pH is the measure of the acidity or alkalinity of a soil using a scale of 3 through 11. A pH of 7 is neutral, acidic soil has a pH less than 7, and alkaline soil is greater than 7. Most plants grow well in soils with a wide range of pH, from about 5.5 to 8.3. Sacramento soils tend to be neutral or alkaline. You may experience an iron or manganese deficiency in a high-pH soil. Symptoms include new foliage that is undersized and yellow except for green along the leaf veins.

Applying fertilizers without knowing which nutrients are deficient wastes time and money, and can lead to salt buildup in the soil. High fertility inhibits the formation of mycorrhizae, which are beneficial fungi that assist the roots in the absorption of water and minerals.

Fertilizing a tree undergoing stress is not recommended because it diverts the tree’s resources from storage and defense and uses it for shoot and leaf growth. This makes the tree more susceptible to stress and less resistant to pests.

Except for palms, fruit and nut trees, the fertilization of established trees is not recommended unless a soil analysis indicates certain nutrients are deficient.

Sunland Analytical Lab in Rancho Cordova offers various soil test packages and water tests. A soil test for a general landscape evaluation costs $87 and includes soil amendment recommendations from the results. Contact or call 916 852-8557.

So, before purchasing that bag of fertilizer, have your soil tested. It’s better for the tree and could save you some money.

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