Manure in the garden

Move that manure!

 When I was a child there were always a few warm spring days when mom was complaining about not being able to open the windows because grandpa had just dumped loads of cow manure in the garden. His garden was only about 20 feet from our kitchen windows. He had a friend who was happy to deliver loads of that fragrant manure every spring. He spread the manure everywhere, from vegetable bed to rose bed.

I know my grandfather was one of those gardeners who waited until around Memorial day to plant so I guess adding that manure in April would have given it time to age enough that it wouldn’t burn the plants. And back then people didn’t worry so much about salmonella and other manure carried pathogens. Or maybe the manure was well aged when it was delivered, I don’t remember.

Any manure you add to flower beds should be well aged, so it won’t burn plants. (Well-aged is manure that’s several months old.)  The burn effect comes from both an overabundance of nutrients such as nitrogen and the actual heating up of the manure as it decomposes. Plants will turn yellow and brown and can quickly die if too much fresh manure is applied near them.

Rabbit and goat manure is not as likely to burn plants even when applied fresh. But it will contain lots of pathogenic bacteria. Poultry manure is probably the worst manure for “burning” plants when fresh. Manure from other animals falls somewhere between.

Aged manure may not burn the plants, but it can still carry bad bacteria. It’s debatable whether we have more problems with salmonella, listeriosis, and other food borne pathogens than we did fifty years ago. But we are more knowledgeable about the diseases they cause. Manure in food gardens should be applied long before the garden is planted, preferably several months before, to prevent bacterial contamination. This is especially true for root crops and leafy greens.

Manure is less likely to change soil pH than common fertilizers, it improves soil structure as it provides lots of organic matter, especially if mixed with animal bedding, and it usually is high in nitrogen.  Manure improves soil aggregates, the way soil sticks together, which lessens erosion and makes a better place for plant roots.

Manure is great for the compost pile and composted manure and bedding mixtures makes an excellent soil amendment. But, it’s an inefficient way to supply plant nutrients. Unless you have it tested, you don’t know what nutrients the manure actually provides. What type of animal produced it, what it ate, what bedding the manure is mixed with, how long the manure was stored and how it was stored all effect the nutrient content of manure. 

There are other drawbacks to manure.  Manure increases soil electrical conductivity, which helps soil hold on to mineral elements. Some of these are salts, which over time, can build up in the soil and harm plants. If manure washes off it can run into surface water, contaminating it.  And it can even contaminate ground water in certain circumstances. Don’t apply manure on slopes or close to bodies of water, ditches, or drains.  Keep it 50 feet away from any wells.

In recent times some manure may contain chemicals that harm plants.  These were applied to hay the animals ate and are excreted in manure. And manure often has lots of weed seeds, especially if it came from horses. A horse’s digestive system moves food through it so quickly that many weed seeds survive the journey. Horses consume weed seed both from pastures and from hay.

The best time to apply manure to flower beds, perennial crops and the vegetable garden is after the plants are dormant and the ground cold, but preferably not frozen. You could apply 6-8 inches of manure if you have it.  If manure is applied before perennial plants are dormant, they may start growing again and that new growth will be winter killed, wasting plant resources. 

Manure applied to frozen ground is more likely to run off nutrients which contaminate nearby water. And if the ground is frozen the nitrogen in the manure will largely disappear before the spring thaw. Adding 3-4 inches of manure before the ground freezes will keep it from freezing for a long while and let soil microbes work it into the soil.

 

Manure is bulky, heavy, messy and smelly. It takes a lot of manure to supply the same nutrients just a sprinkling of fertilizer produces. If you have manure from animals you raise or some one gives it to you every year free then it’s worthwhile to add it to your garden and compost pile. If you don’t know how the manure was produced and stored, and you have to buy it, I would pass.