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how to destroy weed seeds in compost


Composting is one of the oldest ways of recycling based on the biological breakdown of organic material by microorganisms in the presence of air and moisture. The bio-organic waste decomposes during the composting process to produce a soil-like material. The end product of composting can then be used as a natural fertilizer, rich in carbon, nitrogen, and other nutrients, for the soil to improve plant growth while also serving as a natural pesticide.

YES: Kitchen scraps of fruit peels and vegetable cuttings, coffee grounds, tea bags, peanut shells, eggshells, decaying leaves, garden trimmings, grass clippings, straw, hay, soil.

NO: Seeds, weeds, diseased plants, animal products except eggshells (meat, fish, cheese, bones), animal waste (because of possible spread of E. coli), oil, grease, plastic, metals.

Gather organic waste and make sure peelings and plant material are small in length, so that they can break down and decompose faster.

Store in a composting bin or out in the open contained by metal chicken wire or wood fencing, ensuring 1 metre in diameter and height.

Mix dried "browns" (decaying leaves, straw, dry organic material) with moist "greens" (grass clippings, fruit peels, vegetable cuttings) in a 1:2 or 1:3 ratio and pour some soil

Turn the compost twice a month to increase the amount of air. Keep the compost pile damp by adding water (if severely dry) or "greens".

The temperature of the pile should be around 54°C. (Can go up to 63°C if composting to destroy weed seeds.)

The compost is ready when it appears dark and has an earthy smell and appearance.

If the composting pile accidentally contains weeds that produce seeds, there is a way to destroy the weeds and the seeds. By turning the compost to make sure that the weeds are on top of the pile, the seeds will dry out as they are left out in the sun – a process called solarization. The heating of the compost will help to eliminate the seeds. An effective way to increase the temperature of the compost is to create "a greenhouse effect" by spreading out the pile and placing a plastic sheet on top. A compost pile temperature of 63°C will be enough to destroy even the most resistant seeds after one month.

This can be due to a lack of "greens" and moisture.

Make sure the compost pile is damp by increasing more nitrogen-rich "greens". Then, move the pile to a location that provides enough of both sunlight and shade to maintain optimal water drainage. Otherwise, if placed in an overly sunny location, the compost will become too dry to reach the required temperature.

The compost pile should not have an odour other than an earthy soil-like smell, and when done correctly, will not attract insects or rodents.

When the composting process is done incorrectly, the compost pile might have a rotten egg smell. However, there are ways to fix this! If an odour is present, that indicates that materials from the DO NOT compost list or too many "greens" were added, contributing to an increase in moisture and low pH. Fix this by adding more "browns" and turning the compost pile more frequently. Also, consider moving the pile to a sunnier spot to improve water drainage. If the pH is below 6, add limestone to increase the pH back to the optimal range of 6-8.

The compost pile should generally have a neutral pH, meaning that the pH should be between 6 and 8.

The pH can be measured using pH indicator paper, a soil test kit, or a calibrated pH metre. When using pH paper or a calibrated pH metre, dissolve the compost sample into distilled water before measuring the pH, and this will give the pH of compost in water (pHw).

If too acidic (pH below 6), then the pH of the compost can be increased using limestone, mixing the pile more frequently to improve air circulation, and by adding more "browns". If too alkaline (pH above 8), then the pH of the compost can be lowered by adding pine needles, oak leaves, and letting the pile sit without mixing to reduce airflow.

From April to October at Cambridge (201 Savage Drive) and Waterloo (925 Erb Street West, Gate 2) Waste Management sites.

Due to COVID-19, compost and mulch cannot be currently picked up.

Visit the Region of Waterloo Waste Management website for more information.

We want to start composting at our garden located at the Northdale site soon but are not composting at the moment.

How to destroy weed seeds in compost

Q. I was just too busy this fall to add any compost or manure to my garden. Can I still add it this spring?

– Glacier County

A. Overall, fall is the best time to add amendments like compost and manure. This allows them time to finish breaking down into organic matter, and nutrients are more available when plants are actively growing in spring. However, it is still better to add them in spring than not add them at all.

There are two precautions for adding amendments in the spring. First, you may need to add extra nitrogen to the garden. Compost and manure may not be fully broken down and there may be a fair amount of carbon remaining. The microbes that break down the carbon in the compost, making nutrients available, require nitrogen for this process and may “rob” nitrogen from the soil. Keep an eye on your plants and if they seem chlorotic (i.e., green material becoming yellow or white), and add a bit of nitrogen.

Second, be sure the manure you are adding is fully composted and does not contain any herbicide residue. If you use fresh or even aged manure, it may contain weed seeds and/or residue of herbicides used to control weeds. Overall, it is recommended to only add manure-based compost once every seven to 10 years and that it come from a reputable source.

Q. Each spring when I get to my garden I have a ton of weeds. I usually till them in, but I think it is causing even more weeds. Can I spray the garden with Roundup this spring before I rototill?

– Cascade County

A. This is a good question and one that I get quite often. First, if you have a lot of weeds in your garden in the spring and you rototill, it may increase the weed population. When rototilling, you stir up the weed seed in the soil and may redistribute weed rhizomes throughout the garden.

If you are open to the use of pesticides, spraying the garden with a broadspectrum herbicide, such as Roundup, is recommended. This will reduce the number of weeds, especially rhizomatous weeds, and lessen the chance of redistributing harder to kill weeds. In most cases, spray the garden, wait a few days, rototill in the debris, then plant. Be sure to read and understand the label and be aware of the time you spray to the time that you seed. Be aware of your safety and the environment around you when spraying.

Spraying will take care of many of the weeds, but not the seed that is stirred up during tilling. Continue hoeing those weeds into the fall and never let them go to seed.

Finally, at the end of the gardening season, be sure to clean up and remove all the debris and then rototill. If you do end-of-the-year clean-up and sanitation in fall, you will have fewer weeds the following year.

Q. When and how do I use dormant oils?

– Gallatin County

A. Dormant oils, also called mineral oils, are used to manage insects on woody yard and garden plants while they are dormant, generally in winter. These highly-refined oils suffocate insects by blocking air holes they use to breathe. When sprayed in the early spring before bud swelling and bud break, and diluted with water, these oils may be an effective control of many hard-to-kill pests, including aphids, caterpillars that overwinter as eggs, mites that overwinter on the plant, and many scale insects. They are relatively safe to use and have less effect on beneficial insects than many other pesticides. When using dormant oils, always read the label. Be aware that some woody species, including black walnut, Douglas fir, junipers, maples and spruces, are sensitive to dormant oils, so oils should be avoided around them. Do not use dormant oils when temperatures are below freezing, rain is likely, or in combination with other pesticides.