Why is my lawn turning yellow after winter in Moncton NB?

Your Moncton lawn is most likely turning yellow due to snow mould, iron chlorosis from waterlogged soil, or nutrient depletion after the long winter — all extremely common conditions in Maritime New Brunswick that typically resolve within 3-6 weeks as the soil warms and dries. The key is correctly diagnosing which issue you're dealing with, since the treatment differs for each.

Snow mould is the most frequent cause of yellow and brown patches in Moncton lawns after winter. With 200-250cm of annual snowfall and snow sitting on the ground for 3-4 months, the damp, dark conditions under snowpack are ideal for grey snow mould (Typhula blight) and pink snow mould (Microdochium patch). Look for circular patches 6-24 inches in diameter with matted, straw-colored grass. You may see greyish or pinkish fungal threads on the matted areas, especially just as the snow recedes. The good news is that grey snow mould usually only kills leaf blades — the crowns survive and produce new growth once temperatures warm. Gently rake affected areas to improve air circulation and break up fungal mats. Most patches will green up on their own by late May.

Iron chlorosis — yellowing caused by iron deficiency — is another common springtime issue in Moncton. This occurs when soils are saturated from snowmelt, which is typical in April and early May. Waterlogged, cold soil limits root function and iron uptake even when iron is present in the soil. Moncton's Zone 5a-5b location means the ground thaws earlier than inland areas, but spring rains and high water tables keep soils wet longer. Additionally, NB's acidic soils (pH 4.5-6.0) can actually lock up iron and other micronutrients. Once the soil dries and warms to 10°C, normal nutrient uptake resumes and the yellow color fades.

Nutrient depletion after winter is the third common cause. Your lawn uses stored energy reserves to survive 5-6 months of dormancy under snow, and by April those reserves are exhausted. If the lawn didn't receive an adequate fall fertilizer application (a winterizer in late September or October), it may emerge in spring with a generalized yellow-green color rather than the deep green you expect. This is different from the patchy yellowing of snow mould — nutrient depletion produces uniform light color across the entire lawn.

To help your Moncton lawn recover, resist the urge to fertilize immediately. Wait until late May when soil temperatures reach 10°C and grass is actively growing. Raking gently to remove matted debris and improve air circulation is the best early intervention. If yellowing persists beyond 4-6 weeks into the growing season, a soil test will reveal whether the issue is pH, iron deficiency, or another nutrient gap. Lime application to bring pH above 6.0, combined with a balanced slow-release fertilizer in late May, resolves most persistent yellowing within 2-3 weeks of application.

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