Fig. 50: Hand application of fertilizer in a band around an established Fraser fir.
Although fertilization at planting time is not generally recommended, fertilization later in the Christmas tree rotation can often be beneficial. Christmas trees are essentially a foliage crop, and luxuriant foliage with good color is a definite asset when trees are sold.
Good moisture and nutrient relations are of prime importance in producing trees having desirable foliage characteristics. Earlier discussions have emphasized the importance of site evaluation, species selection and control of competing vegetation on nutrient and/or moisture relationships. In this section, the potential of using fertilization for improving foliage characteristics in established plantings is discussed.
As with any crop it would be very desirable to be able to prescribe fertilization needs of Christmas trees on the basis of soil and/or foliar analyses. However, adequate standards for making such diagnoses are not yet available. As a consequence, fertilization needs must be judged largely on the basis of indirect indicators.
Species and site characteristics often serve as a general guide to fertilization in established Christmas tree plantations. On sites with adequate water, species having relatively high site requirements such as some of the spruces, true firs, Douglas-fir and white pine may respond favorably to fertilization on coarse to moderately coarse textured soils (sands to sandy loams) and possibly even on medium to moderately fine textured soils (loams to silty clay loams). Scotch pine does not need fertilization on most sites, but it may benefit from fertilization on relatively dry, infertile areas and may show considerable foliar response to fertilization on a wide variety of sites. It is generally more difficult to obtain favorable response to fertilization with most species on either very dry or wet soils.
Thin, open growth of herbaceous vegetation on sites can also be used as an indicator of fertility needs, especially on areas where there is adequate soil moisture.
A number of materials can be used for fertilizing established Christmas tree plantings. In the absence of more adequate standards for diagnosing needs, applications of balanced fertilizers having 1-1-1 ratios such as 10-10-10 or 15-15-15 are probably as good as any other material. Where nitrogen may be deficient, fertilizers with 2-1-1 ratios (such as 12-6-6 etc.) are appropriate. Applications of high-analysis nitrogen compounds such as urea (45-0-0) or ammonium nitrate (33.5-0-0) can improve foliage characteristics when applied one or two years prior to harvesting. Research in Ohio indicates that foliage density of Norway and white spruces,
Douglas-fir, Fraser fir and Scotch and white pine growing on a variety of sites improved significantly when fertilized with 150 to 225 pounds of actual nitrogen per acre treated. If individual trees are fertilized, from three ounces to one pound of the above formulations will be needed, depending on size. Care should be taken when using high-analysis nitrogen compounds to avoid excess stimulation of succulent growth that may be subject to winter injury. Excess applications of soluble nitrogen compounds can also severely injure or kill small trees, particularly on sandy soils.
Applications of fertilizers to established Christmas tree plantations should be carried out in conjunction with good weed control practices, including judicious use of herbicides in bands or spots around trees. Band applications of fertilizers are generally more desirable than broadcast applications because less material is used and it is placed only in areas where it is needed. Banding also avoids excessive stimulation of herbaceous growth between rows. Methods of banding vary. Hand applications can be used by applying a circular band of fertilizer 8 to 12 inches from stems (Fig. 50), or mechanical equipment can be used. Early spring is probably the best time to apply fertilizers in established Christmas tree plantings. Costs of fertilizer applications vary. Table 6 lists examples of time requirements for equipment and labor using hand and tractor applications.
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| Fig. 50: Hand application of fertilizer in a band around an established Fraser fir. |