Is It OK to Fertilize in Hot Weather?
Avoid fertilizing when temperatures exceed 85°F for cool-season grasses and most garden plants. Heat-stressed plants can't absorb nutrients efficiently and concentrated fertilizer salts can burn roots and foliage. Exceptions: warm-season grasses (Bermuda, Zoysia) actively grow in heat and can be fertilized. If you must feed in summer, use organic slow-release products like Milorganite that cannot burn.
What You Need to Know
Fertilizing in hot weather is risky for several reasons. First, heat-stressed plants close their stomata (leaf pores) to conserve water, which reduces nutrient uptake through both roots and leaves. The fertilizer sits in the soil unused, concentrating as water evaporates. Second, quick-release synthetic fertilizers have a high salt index that draws moisture away from roots : exactly the opposite of what plants need during heat stress. This is how fertilizer burn happens. Cool-season grasses (Kentucky Bluegrass, Tall Fescue) go semi-dormant above 85°F and should not be fertilized until temperatures cool in fall. Warm-season grasses (Bermuda, St. Augustine, Zoysia) are actively growing in summer heat and can be fertilized, but use slow-release nitrogen to minimize burn risk. For gardens, if you must feed during summer, apply in early morning when temperatures are coolest, water thoroughly immediately after, and use half the normal rate. Organic products like Milorganite, compost, and fish emulsion are the safest summer choices because they cannot burn.
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