When should I fertilize trees and shrubs in New Brunswick?

The best time to fertilize trees and shrubs in New Brunswick is early spring, from late April through mid-May, just as buds begin to swell and root growth accelerates in the warming soil. A second, lighter application can be made in early June for trees and shrubs that show signs of nutrient deficiency, but avoid fertilizing after mid-July — late-season fertilizing promotes soft new growth that will not harden off before NB's early frosts arrive in September and October, leading to winter dieback.

Before applying any fertilizer, get a soil test to understand what your soil actually needs. New Brunswick soils are typically acidic (pH 4.5-6.0) and often deficient in calcium and magnesium. A basic soil test costs $30-60 through the NB Department of Agriculture or private labs and tells you the exact pH, nutrient levels, and organic matter content of your soil. Many NB homeowners waste money on high-nitrogen fertilizer when their trees actually need lime to raise pH, which unlocks nutrients already present in the soil. Dolomitic lime is particularly valuable for NB properties because it raises pH while also supplying magnesium, which is commonly deficient in Maritime soils.

For most established trees and shrubs in good health, a balanced slow-release granular fertilizer (such as 10-10-10 or 14-14-14) applied at a rate of 1-2 pounds per inch of trunk diameter works well. Spread it evenly beneath the canopy drip line — not piled against the trunk — and water it in thoroughly. Newly planted trees should not be fertilized in their first year, as the stress of transplanting combined with fertilizer salts can burn tender new roots. Wait until the second spring, then apply a gentle, slow-release formula at half the normal rate.

Flowering shrubs like lilacs and hydrangeas benefit from different approaches. Lilacs prefer a low-nitrogen fertilizer or simply a top-dressing of compost and bone meal in early May, which promotes flower production over leafy growth. Panicle hydrangeas respond well to a balanced fertilizer applied when new growth emerges in spring. Acid-loving shrubs like rhododendrons and azaleas (marginal in NB but possible in zone 5 sheltered spots) need an acidifying fertilizer formulated for evergreens.

Evergreen trees and hedges should be fertilized in early May as new growth begins, using a fertilizer formulated for evergreens (higher nitrogen, often with added iron and sulfur). Cedar hedges in particular respond dramatically to proper fertilization, producing denser, greener foliage. Apply granular fertilizer along both sides of the hedge row and water deeply. For established trees that appear healthy and are growing normally, annual fertilization is not always necessary — a 2-3 inch layer of quality compost spread under the canopy each spring provides gentle, sustained nutrition.

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