Best fertilizer for lawn in autumn

Judith Adam

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October is good time for lawn fertilizer.
October is good time for lawn fertilizer.
October is good time for lawn fertilizer.

The cool nights and mild days of early autumn are just what grass needs to repair itself from the strains of a long growing season that began last April. This is the time to look in garden centres for bags of autumn turf fertilizer, and October is the month to get it spread across the lawn. If I’m able to fertilize the grass only once a season, autumn is the most crucial time, because this is when it benefits most from supplemental feeding.

Blades aren’t growing as quickly as they were in summer, and by month’s end we should be putting the lawn mowers away. The grass remains green well into December, and autumn fertilizer applied in October will go more toward strengthening the plant crowns than into blade growth. All that new food energy will be stored in the crowns for a healthy growth spurt next spring.

Looking through Internet searches for lawn fertilizer products promoted for fall application, I’m confused (and shocked!) at the differences in nutrient (nitrogen, phosphorus and potassium) content. One I found had an analysis of 32-0-10, delivering a whopping amount of nitrogen. Another had a much lower nitrogen content of 4-0-12, with the largest amount of nutrition in the form of potassium.

It’s all a matter of what you think grass needs to be healthy and grow, and I know gardeners frequently disagree about lawn fertilizers. I always try to keep the nitrogen content to a number of 20 or less, because repeated application of high-nitrogen fertilizers can lead to difficult problems such as thatch layers in the lawn. I like the second fertilizer analysis (4-0-12), because it provides a good dose of potassium, which helps build strong cellular walls and maintain good health. But that product gives such a low dose of nitrogen (and not a bit of phosphorus), and I would prefer to have at least 10 per cent nitrogen content. Another product offered 10-0-0, satisfying my interest in nitrogen, but delivering no other nutrients. (Plants absorb fertilizers more effectively when at least small amounts of each nutrient are present.)

I did find a granular shrub and evergreen fertilizer with an analysis of 10-3-6 that’s just right for my concept of how much to feed the lawn. This could be used for any kind of plant, including turfgrasses. But it’s packaged in small 3.75-pound (1.7- kg) bags, impractical for feeding a lawn.

I think there’s still hope for finding an autumn fertilizer product at a local garden centre that will suit my needs. Failing that, I’ll spread two inches (5 cm) of composted manure across the lawn for a good old-fashioned meal of basic nutrients. There’s more than one way to put the lawn to bed on a full stomach.

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2 thoughts on “Best fertilizer for lawn in autumn”

  1. Was waiting for the print edition to comment on this. As I couldn’t find the subject there, here is a short version of my 2 cents worth on it.
    You say you look for a nitrogen (N) content of 10-20% in a lawn fertilizer. The actual N content is less important than the relative concentrations of principal nutrients, N, P and K. Application rate can be adjusted to deliver the desired dosage of a particular nutrient, whatever its concentration in the fertilizer. If you want to apply 1 lb. of N per 1000 sq. ft. of lawn (typical for spring/summer growing conditions), that can be accomplished with fertilizer of any N concentration by applying 1/(fractional N concentration) per 1000 sq. ft. of lawn. The dosages of other nutrients are then fixed in proportion to their relative concentrations in the fertilizer – so choose your fertilizer according to the nutrient proportions you want. For application rate, you can either do the math yourself or follow label directions.
    If you want a balanced fertilizer such as 10-10-10, you can probably find that at a farm supply dealer. Or look for 7-7-7 at Canadian Tire, etc.

  2. Guelph Turfgrass Institute, (a great resource)many years ago recommended an application of a high nitrogen fertilizer as late in the year as possible. This would be absorbed and produce the best green-up in Spring and in fact could be the only application needed for the whole year. I believe it was suggested that we look for a leftover bag of spring fertilizer! Now I see that the fall fertilizers are indeed coming out with a high N ratio. Also Tommy Thomson from Humber always said that our soils need K potassium, more than they need the phosphorus. I am a frugal gardener and have followed this advice with excellent results although I may not even fertilize every year at all! I have had no problems with chinch or other bugs and have a liberal proportion of white clover in my lawn which stays green no matter what! Thank you for another good article and always the wonderful mag. Jennifer W (a “Charter subscriber”) I see you have scillas in your “October” lawn…..


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