7 Ways Manure Can Harm Your Garden: What to Look For
Manure, though smelly, is a wonderful amendment for the landscape. Whether you’re using cow or chicken manure, there are efficient ways to implement the stuff without harming plants, animals, and yourself! Watch for these seven ways manure can harm the garden, and learn how to use it best.
Contents
If you tend to livestock like sheep, chickens, or cows, you’ll have plenty of poop to manage! This animal poop is what we call manure. It may seem like a smelly waste product, but it’s a valuable garden amendment.
The key to using this amendment is allowing for a proper decomposition period. The brown muck is full of nutrients that plants need, but decomposition organisms like bacteria, fungi, and archaea must convert it into a form that plants can use.
Composting is a great way to speed up the breakdown process, though you can also spread the material over the ground and let it decompose in place. No matter how you use manure, avoid hurting your garden, local wildlife, and your family by watching for these harmful symptoms.
What to Look For
These seven symptoms are common signals that something is afoot and manure may be harming your garden. They commonly occur from applications of uncomposted manure, though composted material can also cause harm. Catch these signs early to prevent more problems.
Plants Burning
Burns on leaves, stems, and roots can occur in sites with excessive amounts of composted or uncomposted manure. Too much of the stuff overwhelms the site with nutrients like nitrogen. You’ll notice yellow leaf edges, necrotic spots, and abnormally dark green foliage.
Nitrogen isn’t the only plant nutrient in animal waste; it also has phosphorus and potassium in varying amounts depending on the animal it came from. The most common manures come from cows, sheep, rabbits, horses, and chickens.
Use this chart to help estimate the nutrient levels in your animals’ waste:
| Animal | % Nitrogen | % Phosphorus | % Potassium |
| Chicken | 1.1 | 0.8 | 0.5 |
| Dairy Cow | 0.3 | 0.2 | 0.3 |
| Horse | 0.7 | 0.3 | 0.6 |
| Steer | 0.7 | 0.3 | 0.4 |
| Rabbit | 2.4 | 1.4 | 0.6 |
| Sheep | 0.7 | 0.3 | 0.9 |
If the garden’s soil is already fertile, there’s little need for an application of manure. Only apply it where nutrients are low, like in vegetable beds and areas where you regularly grow crops. When unsure, use a soil testing kit to determine the nutrient contents at the site.
Salt Crusts Forming
Alongside excess nutrients, salt crusts can build up! Though you can’t see the salts, they’re inside the manure. Fresh manure is especially rich in salts, and the buildup can both kill growing plants and prevent future seedlings from sprouting.
To avoid salt damage, compost the waste first, or wait three to four weeks after applying fresh manure before sowing seeds and transplanting seedlings. The salts will leach out after a month, as water helps them penetrate deeper into the ground where roots won’t reach.
Poultry waste has the most salt of any manure, making it the most likely to harm garden plants when used raw. If you’re using waste from turkeys, chickens, or pheasants, consider treating it first or letting it sit for a month before planting new plants.
Wilting Crops
Alongside salts, herbicide residue can persist in manure if animals eat weeds or crops with chemicals on them. The herbicides persist in the manure; when you apply it to the ground, they leach into the soil. Any plants growing in the stuff will quickly wither and die, or they’ll face significant growing issues.
Rather than removing the contaminated amendment after seeing symptoms of herbicide damage, let the chemicals leach out before adding the stuff to your garden beds. Here’s an easy way to test for herbicides in mulch, compost, or manure:
- Plant a bean seed in the amendment.
- Water it and let it grow.
- Watch for signs of damage, like yellow leaves, limp stems, and slow growth.
- If the bean plant grows without issues, the mulch should be contaminant-free.
If you see signs of herbicide damage, consider composting the stuff to help speed up how quickly the chemicals decompose. Hot compost it with carbon-rich materials, or let it sit for a year or more before implementing it in your landscape. Avoid placing it near seedlings, trees, or shrubs, as the leaching herbicides can harm them.
Presence of Pathogens
Pathogens can be deadly! Bacteria and fungi can travel from waste onto crops, soils, and plant debris. Fresh manure is the most likely to have diseases that harm the garden and humans. When you grow crops like spinach or beets in it, the pathogens can travel onto the leaves and into your body when you eat them.
Prevent pathogens in one of two ways: compost the manure, or let it sit for many months before applying it. Hot composting is a quick, labor-intensive method that helps lower the amount of pathogens.
You may apply fresh manure to the soil around leafy greens and root crops, though you’ll have to wait 90 to 120 days before harvesting them. If the plants have a short growing season, apply fresh manure in the fall to see its effects in spring.
Leaching into Waterways
Plants love nutrients, but too many can cause significant problems in areas outside of the yard. Nitrogen is especially troublesome, as it can cause algae blooms in lakes, bays, and other bodies of water. It travels with irrigation water, running off into nearby streams, rivers, and creeks.
If you have a pond or water feature near sites with manure, the nitrogen can upset the natural balance of microorganisms and algae. This is common in climates with lots of rainfall, as the rains leach the nutrients from the dirt and push them elsewhere.
Prevent the ecological harm of garden leaching by applying just enough manure, and not too much. Compost the waste first to lower its nitrogen content, and add repeat doses over a few weeks rather than a single large dose.
Muddy, Soggy Soil
Animal waste can create muddy patches! This is common with thick applications and in gardens with too much mud, clay, or silt. Mixing or tilling it into the ground is a good practice, as it helps incorporate the waste with the dirt to prevent mud from forming.
To prevent muddiness, apply compost in layers between a quarter and a half-inch thick. Rake it in, or place it on top of the ground and let it incorporate itself over time. Blending manure with other mulches like composts, leaf molds, or straw can help lower the risks of future muddiness.
Weeds Sprouting
Like herbicides, weed seeds can persist after animals digest their food. They may eat them when they eat weeds in pastures and fields. The seeds drop out in their waste, and seedlings sprout after you spread the mulch on your crops.
Hot composting is the best way to reduce the likelihood of these seeds sprouting, as the high temperatures kill them during the composting process.
If weeds do sprout, simply pull them before they produce seeds and throw them back on the ground. The pulled weeds will decompose and cover the ground, conserving moisture and protecting plant roots.
How to Use Manure
So, now that we know how not to use this soil amendment, let’s learn how to use it best! There are a few options for us home gardeners—which is best for you depends on how much space you have and how much manure you’re dealing with.
Compost It
Composting is an ideal way to process animal waste. It decreases the nitrogen content, though it increases the material’s soil-boosting qualities. Drainage, water retention, and porosity will benefit from repeat applications of composted manure.
Hot compost is the best way to deal with the material, as it kills pests, diseases, and weed seeds. You’ll combine manure, a nitrogen-rich amendment, with carbon-rich debris like fallen leaves, paper products, and straw.
Nitrogen-rich materials are “greens,” and carbon-rich ones are “browns.” For every scoopful of greens, add two scoopfuls of browns. Turn the pile daily with a pitchfork, and keep it sufficiently moist, but not soggy. You’ll have a ready soil amendment in three weeks to two months after you make the pile.
Spread It
Instead of spending time and labor composting fresh manure, you may spread it over your beds and fields if you’d like. Add it in a layer a quarter to a half-inch thick on a dry, warm day.
To prevent the risk of pathogens transferring to animals or us gardeners, wait some time before letting cattle graze or harvesting crops. Wait three weeks after applying the fresh amendment before letting animals graze, and 90 to 120 days before harvesting vegetables or fruits.
In large fields where cows or horses graze and leave their waste, using a pasture harrow on a tractor can help lower pathogen risks and speed up the decomposition process. If you don’t have a pasture harrow, try using a chain link fence or a similar material on the back of your tractor to break up clumps in your fields.
Give It Away
Sometimes, there is such a thing as too much manure! Rather than using or storing it, you can give it to your gardening friends, neighbors, and family. Master Gardener programs and plant societies, or clubs, typically appreciate heap-loads of free mulch.
If these groups don’t exist near you, consider using online shops to advertise the mulch. Farmers will usually appreciate a free heap or two for their fields.
Store It
Save the mulch for later if you’d rather use it during a different season. Store it in spring for the fall, or keep it safe for the winter, and apply it in spring. Store the mulch in a covered area away from water sources and runoff.
Rainwater can move the nutrients into nearby soil, causing a greening effect on grasses and plants. Enclose the waste with sides of wood, concrete, or brick, and place a tarp on top on rainy days.
If you’re storing it on top of the dirt, consider putting a tarp between it and the ground. That way, the nitrogen and other elements stay inside the mulch instead of leaching into the soil.
Key Takeaways
- Manure isn’t bad for the home garden—it’s incredibly beneficial! Use it correctly to avoid harm to plants, animals, and yourself.
- Consider composting the amendment first instead of applying it fresh to the ground.
- Composted manures have less nitrogen than fresh ones, though they also have more long-term benefits for the soil. They introduce microbes, worms, and porous particles that benefit the ground for many seasons.
- Wait 90 to 120 days before harvesting crops in fresh manure, and three weeks before letting livestock graze the area.
