Why you should fertilize your lawn this fall

Judith Adam

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Corydalis ochroleuca photo by Brendan Zwelling

Have you noticed red tree leaves everywhere? This is definitely the turn of the season, and autumn is upon us. Let’s hope there will be an extended period of frost-free weeks for gardeners lasting well into November, because there’s some serious catching up to do!

Sometimes, I don’t get around to feeding my lawn in spring or summer. There are several reasons for this, but my excuses don’t really matter — the lawn is hungry now and would appreciate a good meal. If you’ve been in a garden centre recently (to pick up some plants on sale), you might have noticed the bags of autumn lawn fertilizer. The first three weeks of October are prime times for feeding turfgrass, and an autumn feeding is the most important meal of the growing season. Cool air temperature in early October slows the growth of grass blades, allowing nutrients to strengthen roots for better winter survival. A significant portion of the autumn fertilizer is absorbed by grass plant crowns and stored for early spring release, just when you want to see a quick green-up (but don’t want to get out in the still-chilly air to feed the lawn).

The nutrient analysis in autumn lawn fertilizers is low in nitrogen (so not to stimulate blade growth), and high in potassium and phosphorus to build disease resistance and cold hardiness. It’s clear that this autumn feeding brings many benefits, particularly when the gardener is unreliable with respect to feeding schedules. (And you know who I’m talking about.) If you’re taking advantage of the season to aerate the lawn (to improve drainage and increase oxygen in the root zone) and repair damaged areas (either with seed or sod), do those chores first and apply the autumn fertilizer last, even as late as early November if the ground isn’t frozen. Your lawn will love you for it!

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10 thoughts on “Why you should fertilize your lawn this fall”

  1. I always read that it is fine to let your grass go dormant in the heat of the summer. However, this summer was so hot that my grass totally died. Question – How do I prevent my grass from dying but still allowing it to go dormant? How could I have prevented this? (I live in St. Catharines, ON)

    I raked out the loose dead grass and sprinkled grass seed. Nothing appears to be happening. Must I had soil also? Was hoping that it was not necessary.

    Thanks so much for your advice.

    • Hi Trudy, My suggestion is to search the Garden Making website for other articles on lawn renovation. This summer was particularly tough on lawns–and many plants–because of the lack of rain and high temperatures. Overseeding in the cool, usually wetter, fall months is a good idea. Best to also add some soil when you overseed and keep the overseeded areas irrigated–once a day if there is no rain–until you see grass seedlings. Usually, grass germinates in 10 to 14 days. Good luck!

  2. Hello Michele (Sept. 20)
    With respect to the lawn, be sure to read the information (usually in fine print) about the grass species contained in the package of lawn seed. Best results will be from a mix of seed varieties, with a content distribution of 40% creeping red fescue, 30% Kentucky bluegrass and 30% perennial ryegrass. (This mix is sometimes labelled as sun and partial shade grass seed.) The creeping red fescue grows strongly in part shade to shade; the Kentucky bluegrass adds lush colour and texture to the lawn; and the perennial ryegrass is a durable grass that withstands foot traffic and acts as a nurse grass to the others while the new seedlings get established. Be sure to cover the grass seed with one-half inch (1 cm) of peat moss, compost, triple mix or aged manure for best germination. To keep the lawn green during droughts, you might want to consider adding white clover seed next spring. You can purchase it in spring, in the grass seed section of garden centres or online from oscseeds.com.

    What a frustrating season this has been for your clematis. I suspect the inordinate amount of rain we had in southern Ontario this spring caused more than one kind of fungus problem for them. The two that appeared to die completely may have succumbed to clematis wilt, a fungus disease that attacks the stems near soil level, blocking the movement of moisture to upper parts of the plants. This infection can collapse the vines for a season, but often they recover and reappear the next spring. The only thing you could possibly do now is move them to a new location (and watch for recovery), or improve drainage close to the plants by digging in coarse builder’s sand and shredded leaves. But I would leave them where they are, and wait and watch for signs of life next spring.

    Those clematis that developed crispy leaves and failed to bloom, and the others that did bloom, but have yellowed leaves, are also probably suffering from a residual fungus infection generated in spring moisture. My thought is that all, or most, will recover next year. Once fungus infections get a foothold in plants, it’s difficult to intervene during the current season. The most you can do is try to lessen the accumulation of moisture to encourage recovery. We live in hope!
    — Judith

  3. Hi Judith!
    I’m about to revive an ancient and ugly lawn with topsoil, seed and then fertilizer. Any recommendation for grass seed for a well-trampled, clay base, half-shade old lawn?
    Also —am desperate about my many clematis. I have at least two dozen, of all types. This year, two always-flourishing ones died completely, two developed dead, brown, crispy leaves early in the season and did not bloom, and one had some blooms but yellow leaves. All have been magnificent for about 10 years. True, I didn’t fertilize this year…but could that lead to such dreadful results? As clematis are my favourites, I feel quite frantic!

  4. To Henry, Sept. 29,

    Oh Henry, this is a problem. Quack grass is an aggressive weed grass, spreading both by seeds and underground rhizomes. It's hard to beat. If you go so far as to remove the turf entirely and put down a new lawn, be very sure that every bit of the underground rhizomes are removed, because any left in place will grow again. (Dig out a healthy clump of quack grass to study the root system, and know how to recognize the rhizomes.) If you should decide to replace the lawn this season, grass sod can be used quite late, even into December. To make a new lawn from seed, better to wait for spring.

    The best organic herbicide available for use is acetic acid, and you can buy this at a garden centre. It's a 20% vinegar solution that kills the tops of young weeds (requires repeated applications). But it will also top kill any green tissue it hits, so isn't good for using in a lawn where it will damage the grass species you want to keep.

    Alternatively, you can re-seed the lawn twice a year (spring and late summer) to encourage a thicker growth of premium grasses, and weed out the quack grass as much as possible. You might be able to achieve an acceptable balance that way. Keep the lawn mown to about 2 inches (5 cm) high, and that will discourage the quack grass from setting seed. Good luck!

  5. To Yvonne, Sept. 29

    Hi Yvonne,

    Yes, your lawn is really going to love you! Timing will be important. Get the grass seed down soon as possible. Be sure to cover it with a generous 1" (2.5 cm) layer of peat moss, or small leaves, or triple mix (from a bag), or even light garden soil (not heavy clay). Grass seed germination is always more successful when the seed is covered. Consider using a seed mix with lots of quick germinating perennial rye grass in it. Kentucky bluegrass takes much longer to germinate, and better to use in the spring when you have more time. Keep the seed wet.

    Delay the fertilizing until quite late, perhaps even early November, to let the grass seeds get a start before a big meal is delivered.

    You haven't mentioned your location, but it's probably safe to say that you absolutely don't need to use lime. Many Canadian regions already have alkaline soils, and lime will only increase that condition. Lime can be used where soil pH is quite acid, pH 5.5 or lower. If you have alkaline soil, adding lime will make a difficult growing condition for grass. Best not to use. And thanks for visiting my blog! P.S. Good news — the vine clips are very inexpensive.

  6. I really enjoyed this article. We were planning to both overseed and use the winter lawn fertiler, so it's good to know that we should overseed first and fertilize a few weeks later. I've heard we should lime about the same time we fertilize. Any opinion?

    Also, I had no idea there was a clematis that bloomed into the fall – must look for this one – and I was wondering about clips as I have a honeysuckle that's also wasted scrambling along the ground. What's a bit more money at Lee Valley … they get lot's of mine already. Trick is to get out with only what I went for… thanks for the all the great information.


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