By Ron Alexander
Guidance in tree and shrub fertilization has changed over time. The University of Maryland (from Fertilizing Trees and Shrubs) currently suggests that:
“In most landscapes, healthy trees and shrubs do not require fertilizers, especially when they reach their mature size [because] trees and shrubs absorb nutrients applied to adjacent turfgrass.” But, of course, this does not always occur – many trees and shrubs do not receive excess turf fertility, and mature trees growing in poor soil conditions could certainly benefit from infrequent fertilization, using slowly releasing nitrogen.
Remember, if a plant’s fallen leaves are not left to degrade around them, that same plant will need additional fertility. The University of Maryland (UMD) further warns against improper fertilization at plant establishment, especially when using quickly releasing nitrogen. When placed in the planting hole, quickly releasing nitrogen fertilizers can burn young roots. According to UMD, “research studies show most of a plant’s energy is directed to root growth during the establishment period. The application of [high rates and quickly releasing] nitrogen during this period seems to suppress root growth rather than enhance it.”
So here’s what we suggest: The safest way to fertilize trees and shrubs is after planting is completed using a granulated (non-liquid) complete fertilizer containing slowly releasing nitrogen. Surface apply the fertilizer around the tree after the planting process is completed and the soil is brought to grade. The tree or shrub should then be watered in, then the fertility applied, followed by mulching. For Cured Bloom, that means applying it onto the soil surface around the tree (or over the planting bed), then gently raking and/or watering it into the soil surface, then mulching over the treated area. Remember, fertility should initially be applied under the drip line of the tree, and as it grows larger outside the dripline, depending on the trees known rooting pattern. For a planting bed, apply fertility over the entire planting area. Note that fertilizer rates for trees are no longer based on trunk size or caliper, but on root system spread.
Virginia Tech’s fertilizer recommendations for established trees and shrubs are 1–6 pounds of actual nitrogen per 1,000 square feet of root zone. Evergreen shrubs and trees need less (1-¬3 pounds) nitrogen, while deciduous trees and shrubs commonly need more (3-¬6 pounds). Further, younger trees and shrubs generally receive higher rates of nitrogen than mature plants. Finally, fertility rates should be reduced when plants are growing in root restricting areas (e.g., sidewalk cuts, parking lot islands), where roots of multiple plants overlap, and in foundation plantings near homes and buildings.
Since Bloom provides slowly releasing nutrients, it is easier and safer to use as a nutrient source, and it also provides needed organic matter. The best product to fertilize trees and shrubs with is Cured Bloom.
• Note that four bags of Cured Bloom (25 pounds per bag x 4 = 100 pounds of product) will provide approximately 1.5 pounds of actual slowly releasing nitrogen, as Cured Bloom has a 1.5-1.5-0 guaranteed analysis. Apply a 25% greater volume of Woody Blend for a similar nutrient addition.
. • In most cases, applying 1.5–2.25 pounds of nitrogen per 1,000 square feet of root zone is a good initial application rate. So apply 4-6 bags of Cured Bloom per 1,000 square feet of estimated root zone (or planting area) or 10–15 pounds per 100 square feet of estimated root zone. 3-4 cubic feet of Woody Blend will supply a similar amount of nitrogen per 1,000 square feet of root zone.
• Watch how the trees and shrubs react over time before reapplying. Note that most tree and shrub planting areas should only be fertilized once every 3 to 4 years.
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