Stakes
Stakes or boluses of compressed fertilizer that can be driven or inserted into the soil are convenient, if expensive ways to supply nutrients to trees and shrubs. If applied deeply enough, they have the advantage of not promoting excess turf growth. The number to use and ratio of nutrients can be determined by weight, just as with granular fertilizers, according to soil test recommendations. However, most people simply follow the "ballpark estimate" on the package directions. Stakes are slow to dissolve, and can be used most any time of year. A larger number of smaller stakes may be more effective than fewer, larger ones because it is hard to guess just where the roots are in the soil.
Drill holes
A major advantage of the drill hole method is the opening of heavy (clay) or compacted soils, which allows air and fertilizer to penetrate. With this technique and liquid injection, you avoid the excess grass growth that surface applications cause in turf areas.
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Make small holes using a drill or soil auger, 1 1/2 to 2 inches wide and 12 to 18 inches deep. |
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Start about 3 feet away from the trunk and make the holes in concentric circles moving out a few feet past the drip line (the tips of the branches). |
Root feeders
Liquid fertilizer injected into the soil is rapidly taken into the plant by the roots, so injection is a good way to apply nutrients. Also, the addition of water to dry soil is desirable during periods of drought. Injection sites should be 2 to 3 feet apart, depending on the injection pressure, and 15 to 18 inches deep for trees. Follow equipment instructions to minimize root damage and keep injectors away from the trunk.
Fertilizer Spreader
Surface applications with a lawn-type spreader should be made at the lawn rate, or in portions that result in no more than 1 pound of actual nitrogen each time, per 1000 sq ft, to avoid damage to the turf. Time the applications in mid to late fall or early spring so that at least 3 weeks and a period of rain or irrigation come between applications. Do not apply close to the trunk. See How to Calibrate a Fertilizer Spreader .
Foliar Spray
Leaves can absorb some fertilizer nutrients directly, with a faster change in deficiency symptoms, but soil applications last longer. The following situation is one in which foliar application has value: In some parts of Michigan, manganese deficiency has been observed in maple trees growing on highly alkaline limestone soils. Manganese sulfate or manganese chelate foliar sprays have improved foliage color and general appearance. When using these or similar compounds, be sure to follow manufacturer directions.
Injection into tree trunks
Similarly, oaks in the red/black oak family, particularly pin oaks, develop chlorosis when the roots are unable to take up iron in alkaline soils. On the MSU campus where the soil test often reveals pH of about 8, some oaks have been treated with injections into the trunk with an improvement in appearance that lasted several years. Older methods of implanting nutrient capsules into trees made more and larger wounds, which is not recommended by MSU arborists.