Leaf drop and fall colour is visible on some 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 zone issue (dry, road salt etc.). Except for those stressed trees, fall colour seems to be late this year. Warm, sunny days and cold nights give rise to the most spectacular fall colours and so its likely that these cloudy days and warm nights are stalling colour development this year.
Up to half of the annual fertilizer requirement may be applied to field and landscape plants, after shoot growth ceases (mid-September to mid-October). Did you know that Autumn is a major root growth period for woody and herbaceous perennials? Roots will grow and absorb water & nutrients whenever soil temperatures remain above 5°C (conifer roots will grow at even lower temperatures). So if you are fertilizing this fall, applications to deciduous trees should come before evergreens.
By splitting annual fertilizer requirements into separate fall and spring applications, 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 much (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 and these conditions lead to better nutrient uptake and reduced losses due to runoff.