The lone voice of horticultural reason

Don’t fertilize perennials, trees, or shrubs after August 15th.

After becoming accustomed to fertilizing around our yards and gardens we sometimes forget that we are growing different kinds of things, and that not all plants on our property benefit from late-summer feeding.

Perennials, for instance. Don’t ever fertilize after mid-August, thinking that your plants need a little boost to help them through winter. All that happens is they get jazzed up heading into fall, when cool nights and the sun’s lower intensity are trying to steer your perennials toward dormancy. You’re whipping the horse when you’ve already crossed the finish line and should be slowing down. Fertilize your mums and fall-blooming perennials on or just before August 15th, but any perennial that bloomed in June or July or already in August has no need for it.

There used to be a theory that you should fertilize trees and shrubs in the fall, but now more and more experts are realizing what’s the point? You were always told you were “fertilizing for next spring.” Well, lay the fall fertilizer down around your shrubs or trees and then get a very long fall, or December warm-up with no snow cover, and if the ground hasn’t properly chilled the plants can break into new growth that won’t have a chance of surviving winter. Wait and fertilize in spring, when you’re full of vim and out there cleaning around the beds and laying fresh mulch.

The only fertilizing you need to do is to continue to fertilize annuals in beds and in containers, and your late fall lawn fertilizer application (end of September in Zone 3, mid-October in Zone 4, end of October in Zone 5). Lawn grasses are different. A good fall blend fertilizer has relatively low Nitrogen (N), so you’re feeding your lawn a little phosphorus (P) and potassium (K) in the fall when it is stockpiling nutrients into the roots to help survive winter, and then there’s some left over in the ground, waiting to be taken up in spring.

Don Engebretson
The Renegade Gardener