The Best Time to Manure the Garden

Many years ago now (much more than I care to admit), I lived in the country and ran a small market-gardening business with my partner at the time. Occasionally, one of our neighbors would arrive by tractor with a trailer full of manure. Other times, we used manure from our own laying hens. Depending on the situation or the time of year, this manure went straight into the garden or was added to the compost heap. All this manure was absolutely free! An excellent source of nutrients for our fruits and vegetables.

Many of you “close” your vegetable garden at this time of year. I’m often asked if autumn is the right time to spread manure in our vegetable garden. It’s usually recommended in the fall or spring, but why? And is there a better time than the other?

Fumier au potager
Photo: Getty Images

Late Summer, Fall or Spring?

Before you start, it’s important to understand that, like compost, manure feeds the soil, not the plants, and it’s the soil that will pass on nutrients to your fruit and vegetables, through the action of decomposition, once the manure has decomposed. Compost and manure are soil conditioners that improve the fertility and structure of the soil, rather than fertilizers.

Although it’s possible to spread manure in the spring, I suggest doing so in late summer or autumn, for health reasons. To avoid contaminating your crops, it is recommended to wait at least 90 days after applying fresh manure before harvesting vegetables, and 120 days for vegetables that come into contact with the soil, such as leafy greens or root vegetables. Animal manure may contain bacteria such as E. coli or salmonella.

For example, if you spread your manure on October 1, but the ground freezes 45 days later, decomposition will stop until the ground thaws. Let’s say the ground thaws on April 1st, you’ll have to wait at least 45 days after that to harvest, and even 75 days, i.e. between mid-May and mid-June! Now think about your first harvests of the year: lettuces, spinach, radishes, peas and so on. These are all vegetable plants that are ready to be harvested quickly. For example, if you plant radishes on May 15, they’ll be ready to harvest around June 15, just in time! So, the moral of this story is, don’t wait too long before putting your manure in the garden!


For Late Crops

However, if you intend to use your manure for your tomato plants, there would be no problem in doing so in the spring. Since tomatoes are transplanted from late May to late June, depending on the region, and take a few months to bear fruit, the 90-day deadline will be respected if you spread your manure early enough. The same applies to fruit and vegetables harvested in late summer or autumn.

It has to be said that these periods often coincide with times when there’s nothing going on in the vegetable garden, which makes spreading much simpler. Most of the time, this is what determines when to use manure.

Another alternative is not to use manure for vegetables and fruit that are harvested early in the season. So there’s no need to worry about contamination.

Composting Manure

If you’re still worried about contamination, you don’t have to spread fresh manure directly in the garden. You can also compost it, which will eliminate the bacteria and weed seeds that might be found there… if our compost is well made! Here’s how:

  1. Make sure your manure pile is at least 30 meters (100 feet) from a water source.
  2. Make layers of around 10 cm (4 inches) of manure and 20 cm (8 inches) of leaves, straw or other carbon-rich material, to a minimum height of 1 meter. Your pile should be at least cubic yard to achieve the heat needed to kill bacteria and weed seeds. If your manure already contains a lot of straw or wood shavings, you’ll need to adjust the amount of carbon-rich material.
  3. Add water. Your compost heap should be damp, but not wet.
  4. Turn your compost pile after it has reached a temperature of at least 55? (131°F) for a minimum of 3 days. You’ll probably notice that the pile will have shrunk thanks to the decomposition process. Repeat the process every two weeks for 2-3 months, or until there are no recognizable pieces of original material left.
  5. Spread in the garden!
Compost de fumier
Photo: Maria Firman

Manure Problems

Apart from contamination, using manure in the garden could cause a few problems, the first being the presence of seeds that will germinate in the vegetable garden. Straw is often used as bedding for farm animals, and it’s not uncommon to find straw seeds in manure for this reason. As mentioned above, the manure composting process will eliminate these seeds.

It’s important to note that meat production often involves the use of growth hormones. If this bothers you, or if you want your garden to be organic, make sure that the farm from which your manure comes is also organic.

Is There Such a Thing as Too Much Manure?

Repeated or excessive application of fresh manure can also cause an imbalance of nutrients in your vegetable garden soil. Manure can have a different composition depending on the animal that produces it. Fresh manure often contains high levels of nitrogen. An excess of nitrogen or mineral salts can cause “burns”, which are, in fact, a physiological imbalance that prevents water absorption or cellular respiration. Be careful not to use too much; 2 to 5 cm (1 to 2 inches) should be enough. Ideally, manure spreading should be follo by a soil analysis. Composting manure helps enormously by transforming nutrients into more stable forms.

Excessive levels of certain nutrients, such as nitrogen, can also be harmful to nearby watercourses. Avoid over-watering to prevent leaching. Mulching or using green manure is always a good idea in the vegetable garden, manure or not, to prevent erosion and leaching. Excessive nutrients can also have a negative influence on soil flora and fauna.

In Quebec, the use of manure in agriculture is regulated. Under normal circumstances, its use is permitted between April 1 and October 1, and prohibited on frozen or snow-covered ground. Verify the regulations in your area.

Manure, a nutrient-rich soil improver that is often free of charge, but should be used with care!

Mathieu manages the and websites. He is also a garden designer for a landscaping company in Montreal, Canada. Although he loves contributing to the blog, he prefers fishing.

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