Fertilization is an important part of landscape maintenance. Just as you cannot eat enough food on Sunday night to get through the week, we cannot expect our actively growing plants to get by on one yearly feeding application either.
Unfortunately, fertilization can become complex and confusing if the gardener is swept away by the wide variety of fertilizer products on the market today.
Which analysis is best? A soil test, available through your county Extension office, is the best way to determine which fertilizer analysis is best for your soil. But as a general guideline, most ornamental plants benefit from a fertilizer having its primary nutrients (nitrogen, phosphorus and potassium [N-P-K]) in a 3-1-2 or 4-1-2 ratio. This would be an analysis such as 16-4-8 or 12-4-8.
The analysis is on the fertilizer bag or box, and the three numbers refer to the amount of nitrogen, phosphorus and potassium respectively.
UGA Extension suggests using these ratio-type fertilizers because shrubs use a large amount of nitrogen but they do not need a lot of phosphorous, as it accumulates in the soil. However, if the above analyses cannot be found or if you are on a new site where phosphorous has never been applied, then you can still use a general-purpose fertilizer, such as 8-8-8 or 10-10-10.
For optimum growth of young shrubs, ground covers and trees, three to five applications are recommended at 6- to 10-week intervals from March to August. Application frequency varies with the amount of slow-release nitrogen in the product, so consult the label for specific recommendations.
Established trees and shrubs will benefit from one to two applications during the growing season. Annual flowers and roses should receive applications at four- to six-week intervals from March to August. When using slow-release or specialty fertilizers, follow the manufacturer’s recommendation on the container.
When you purchase the fertilizer, make sure it is not in a “weed-and-feed” formulation that contains a postemergence chemical that kills weeds. Weed-and-feed products that contain postemergence herbicides can injure plants if applied to shrubs and flowerbeds.
Also, note if the nitrogen component of your fertilizer is all or part slow-release. If it is a slow-release material, be certain to follow all label directions. Make sure that you do not exceed the recommended rates. This is especially important since the danger from salt injury is particularly great during the hot summer months.
When applying the fertilizer, broadcast the amount evenly over the root system rather than placing the fertilizer in only one or two spots. This allows even nutrient uptake through the plant’s roots and helps avoid concentrating the fertilizer material, which can result in root damage or death.
There is also no need to remove the mulch materials like pine bark or pine straw, as the fertilizer nutrients will wash through them right into the plant’s root zone. After applying the fertilizer, always water it in thoroughly.
Trees growing in turf areas will obtain nutrients from the fertilizer that is applied to the turfgrass. Do not apply excess fertilizer to turf in an effort to feed trees, as injury to the turf may occur. Rather, when fertilizing trees broadcast the fertilizer over an area extending two to three times the canopy spread, if possible.
Research has shown that tree roots grow far beyond the canopy spread on established trees. Do not concentrate fertilizer in holes drilled under tree canopy. Research shows that broadcast application results in better growth.
If you have questions about fertilizing your shrubs, call the Liberty County Cooperative Extension office at 912-876-2133 or visit our office at 100 Main St., Suite 1200. We are located inside the historic courthouse in downtown Hinesville.