Leaf drop and fall colour is visible on trees and shrubs in the landscape. This is especially true of woody plants on roadsides, high sandy knolls or compacted sites. In some cases where individual specimens are entering senescence earlier than others of the same species, it might indicate a root issue. Some areas of the province have received above average levels of precipitation this summer. But despite that, some plants entered senescence early. It happens every year and the environmental cues (light intensity, day length and night time temperatures) have a very strong influence on our landscape trees. Fall colour is peaking or just passing peak right now in Muskoka and Parry Sound. Southern Ontario fall colour is expected to peak during the next week.
Up to half of the annual fertilizer requirement may be applied to field and landscape plants, after top growth ceases (mid-September to mid-October). Autumn is a major root growth period for woody and herbaceous perennials. Roots will grow and absorb nutrients whenever soil temperatures remain above 5°C (conifer roots will grow at even lower temperatures). By splitting annual fertilizer applications into fall and spring, we can actually maximize plant uptake of important macronutrients like nitrogen. Potassium is another important element in fall fertilizing and can also help improve tree health. Always conduct a soil test before adding nutrients like phosphorus, since so many soils already contain adequate amounts of this nutrient. For more information on fertilizing trees, see OMAFRA Guide 841, Guide to Nursery and Landscape Plant Production and IPM (starting on pg. 1).
Several evergreen nursery growers have shifted some (or all) of their fertilizer applications to the autumn and have reported much better colour, quality and improved growth the following spring. Soils in the autumn are usually warmer and less saturated than they are in the spring, these conditions lead to better nutrient uptake and reduced losses due to runoff.