We have a delightful vegetable garden. Each year I add compost and peat moss and then rototill it all in before planting . I am thinking of adding some well rotted cow manure, which I can pick up from a local farmer. However I have read that this can introduce undesirable bacteria which could have deleterious effects even to the point of food poisoning from the harvested vegetable. Is there any evidence for this is , is this correct?
Thank you for contacting the Toronto Master Gardeners’ with your question about using cow manure in the vegetable garden. Harmful pathogens can be transmitted with the use of fresh or insufficiently composted animal manure on vegetable crops. Fresh animal manure can also burn plants due to its high ammonia content. However, fresh manure can be applied to the garden when a minimum of 4-6 months will elapse before planting to allow for pathogens to be killed. Typically fresh manure is applied in the fall in areas to be planted in spring.
In your case, the plan is to use well rotted, composted cow manure, which provides nitrogen and other nutrients to garden soil and can help to improve soil structure. Properly composted manure will have been through a process where sufficient temperatures were reached for a specified amount of time to kill harmful pathogens. If you are sourcing your manure from a local farmer it is important to ensure that such a process has been followed. The Federal and Provincial governments have regulations regarding this process and I have attached information from Ontario below. If you can’t be sure about the manure you are sourcing, you may want to consider applying it in the fall to benefit the following spring’s planting. When you are applying composted manure, depending on your growing area, you may find that light tilling with a broad fork or pitch fork is all that is needed. This will incorporate the manure while helping to preserve your soil structure and beneficial soil microbes.
West Coast Seeds provides a useful summary of different types of manures; and the University of Wisconsin has a helpful page regarding use of manure in the home garden that you may be interested in. I have attached both links below.
Best of luck with your vegetable garden this spring!