No good gardener ever turns down the offer of a load of well-composted horse manure. Some may even go weak at the knees at the very mention of muck. Why? Because horse manure is a fantastic natural fertiliser, soil conditioner and promoter of earthworms. For leafy plants, always hungry for nitrogen, there really is nothing better than a decent pile of poo. Nitrogen is quickly leached from the soil during the winter months, so an annual application of manure provides the perfect organic top-up. Flowering and fruiting plants also require potassium and phosphorus and although horse manure contains less of these elements, they are not so easily lost from the soil. Both can be supplemented using blood, fish and bone, which I apply liberally to our allotment at least twice a year. Now you know why our dahlias and sunflowers look so happy!
The big challenge with horse manure is getting hold of it. Chances are, if you live in the countryside, you already have a trusted source. If not, ask around and someone will be willing to share their dirty secret with you. Once located, you’ve got the challenge of getting it home and on to your garden. Horse manure is, by its very nature, bulky and you need a fair amount of it to make a difference. It can also be heavy, especially when wet. If you can get it delivered, do so, and take as much as you can deal with. A tonne of manure does not go as far as you might imagine. If you have any left over, it can be left in a corner to continue rotting down until you are ready to use it, or there will always be friends eager to take if off your hands. Be sure to know where your horse manure has come from and how it’s been stored, as occasionally it can be contaminated with weedkillers, the roots of perennial weeds or weed seeds. Do not be concerned about the appearance of straw, wood shavings or sawdust. Much of the value of manure is in the urine-soaked animal bedding, which is particularly high in nitrogen. However, if it’s still very loose and yellow, your manure has not rotted sufficiently. Until the natural matter breaks down properly, nitrogen will be ‘robbed’ from the soil, which is the opposite of what you want. As ever in gardening, patience is a virtue.
We are fortunate, because every January our friend drives down from North Kent with a horse box full of ‘black gold’. This magnificent stuff has been rotting down for five or six years, by which time it’s scentless, crumbly and the colour of a decent chocolate brownie. Each shovel-full is positively writhing with small red worms. Age is important, because fresh horse manure can be so high in ammonia that it will damage the leaves and roots of your plants. At this stage it will be smelly too. Some sources suggest it’s fine to use horse manure on the garden after three to six months, but at this age it could still be fairly coarse, caustic and bulky. After a few years it will have started to compost nicely, and whilst some of the nutrient levels may have diminished, the texture of the manure will be greatly improved. After five or six years, there is very little sign of straw and the manure is a beautiful, friable consistency.
Once you’ve got hold of your manure, you have a choice of what to do with. Spread over beds and borders, or beneath trees in autumn the earthworms will have done much of the work for you by spring. If applied over winter or in early spring, it might help to fork manure in lightly to distribute it evenly through the upper layer of the soil. I tend to be lazy and leave this until I am ready to plant the bed and then the manure can be turned in at the same time as planting. If sowing seeds, it’s wise not to sow directly on to a manure mulch as it will be too rich and too lumpy for successful germination. If you do want to dig your manure in, then add it to the bottom of trenches as you work. Adding manure to soil is a brilliant way of improving its water retention. Crops like sweetcorn, Brussels sprouts, kale and runner beans will reward you for adding generous helpings on a regular basis. As for how much to manure to apply, you can’t really overdo manure as you could chemical fertilisers. As long as it’s not cascading over the top of your raised beds it’s fine and will soon settle down once the worms get to work. Where you don’t want to apply manure is any place you’re hoping to establish wild flowers. Manure will make the soil too rich, encouraging competing coarse grasses and perennial weeds to take over.
Other animal manures are available, from cows, pigs and poultry for example, but rarely are these used alone or in quantity because they are very concentrated. Horse manure is much the best general fertiliser because it’s rich in organic matter and much more mellow. Spent mushroom compost is a good structure improver, but not that useful for adding nutrients to the soil. It also tends to be alkaline, so should not be applied to already alkaline (chalky or limey) soils like ours here in Thanet.
Any time between now and March is fine to add horse manure to your beds and borders provided it’s well rotted, if it’s fresher, you should apply it in autumn and let the winter weather take some of the raw strength out of it before planting. Poor, light, dry soils tend to benefit the most from any kind of organic matter, as it helps to add weight and conserve moisture. Soil where manure is applied annually for three years is said to contain ten times the number of earthworms and that’s certainly noticeable on our allotment.
Although there is some best practice when using horse manure on your garden, the main thing is to get on and add it. Provided it’s not fresh out of the horse’s derrière, you cannot go too far wrong. TFG.