Nursery plants usually require fertilization to promote healthy growth and bring the plant to the harvest stage as rapidly as possible. Due to the variety of sizes and production methods, it is predictable that the methods of fertilization will vary. As is the case with other cultural procedures, grouping together plant species that have similar fertilizer requirements will make the fertilizer application process easier for the grower.
Small plants growing in ground beds usually are fertilized once a year. Typical rates of application are:
• needled evergreens 4 lb. per 1,000 sq. ft.
• broadleaved evergreens 3 lb. per 1,000 sq. ft.
• deciduous shrubs 5 lb. per 1,000 sq. ft.
Small plants growing in containers need more frequent fertilization during the growing season because of the limited amount of media around the roots. These plants lack the nutrient reserve that is available in ground beds. Container-grown crops may be fertilized with dry, slow – release fertilizers or during irrigation with the fertilizer injector systems described in Chapter 20.
Plants growing in the field usually have dry, low-analysis fertilizer or manure incorporated into the soil before planting. After planting, nitrogen fertilizers are usually added annually. Typical rates of nitrogen application for field production include:
• needled evergreens 175 lb. per acre
• broadleaved evergreens 125 lb. per acre
• deciduous trees and shrubs 225 lb. per acre
Actual rates are dependent on the crop, the soil type, and the length of growing season. Rather than applying all of the fertilizer at once, it is usually applied in two or three applications. A spring and early fall, or a spring, early summer, and early fall application schedule allows the most efficient use of the fertilizer by minimizing nutrient loss due to leaching. Further cost efficiency is made possible by applying the fertilizer as side dressing (applied along the side of the rows) rather than broadcasting it over the entire field. Side dress applications are also safer for the off-site environment since the potential for chemical runoff is lessened.
Regardless of how the fertilizer is applied, all applications of nutrients should be discontinued with the approach of fall to allow the stock to harden-off before winter sets in.