Around mid-October each year, I give up on my garden, till or rake away all vegetation and plant annual ryegrass. I also take down the fencing that helps keep the deer out during the growing season so I can more easily till and plant the garden the following spring. I do not mow the ryegrass and it grows tall and becomes green manure for next year’s garden.
I’ve noticed in the last two days with all the snow that the deer are eating the tips of the tall ryegrass coming through the snow in my garden. I’ve also noticed an abundance of deer feces on the white snow in the area.
I know that the snow will melt and the deer pellets will disappear in the tall ryegrass, but should I be concerned about all the deer feces where I will be growing tomatoes and other vegetables this spring?
This is a fantastic question! Unfortunately, I'm not going to give you a straight answer. But first, let me applaud you for your use of a cover crop over the winter in your vegetable garden. Not only does the annual ryegrass prevent erosion and add organic matter, it also recycles some nutrients that might otherwise be leached away.
Regarding the issue of deer visiting the garden, you are wise to use a fence to keep them out. There is indeed a risk that the deer droppings (or droppings from other wildlife) would contaminate your harvest with pathogenic organisms. However, that risk drops as the time between manure "deposits" and garden harvest increases.
As a point of reference, the National Organic Program recommends 90 days between the application of raw manure (as a fertilizer) and the harvest of a crop that does NOT come into contact with the soil. It recommends a 120 day interval for crops that DO come into contact with the soil (e.g. leafy greens and root crops). I understand that the Food Safety Modernization Act is going to require a 9 month interval.
It's also worth considering who will be eating the produce. Pregnant women, the elderly, young children and people with illnesses are examples of those who may be at higher risk.
Hopefully this information will help guide your decision. As a long term solution, you may want to consider permanent fencing that stays up year round.
You may find the following webpages to have some helpful additional information:
- Wildlife and Animal Management practices from the Good Agricultural Practices Program - http://www.gaps.cornell.edu/dt-wildlife.html
- Soil Amendment practices from the Good Agricultural Practices Program - http://www.gaps.cornell.edu/dt-soil.html
All the best and happy gardening!