Today some gardeners and commercial growers decide to avoid adding animal products to their compost or to their land. The motivation not to use animal products doesn’t necessarily come from a vegetarian or vegan impulse but can be a practical solution to a logistics problem. Unless you keep animals on the premises there will be some heavy manual work involved in getting horse manure compost (or cow) onto your plot. Here are some reasons you might want to add a little animal dung to the pile and some reasons you might prefer to go it alone.
Animal manure is full of nitrogen. Straw bedding (carbon) soaks up animal urine (phosphorus and more nitrogen) and collects the dung to provide the perfect mix of nitrogen and carbon for composting, quickly.
Nitrogen is a prime plant food or ‘fertilizer’, along with phosphorus and potassium. Essentially nitrogen helps leafy growth, phosphorus supports the roots and potassium the fruit and flowering processes. There are many other important minerals required for healthy plants but not in the quantities of nitrogen, phosphorus and potassium. These three are the nutrients supplied by synthetic fertilizers that can be bought in granule or pellet form. Although easy to purchase and apply — no lugging heavy plastic bags home — they aren’t good for the soil and therefore for your plants in the long term. Artificial fertilizers are water-soluble and will wash away as it rains or if you irrigate. As with all liquid fertilizers, natural or not, the effect is short lived and reapplication is required.
The environmental problems associated with artificial fertilizers are that energy has to be used to manufacture them, they use virgin resources that take energy to extract and they then leach into natural waterways as the soil can’t hold onto them. The leaching leads to excess growth of algae that can choke the streams and lakes and even seas by blocking out the light from other aquatic organisms and using up the oxygen. Known as eutrophication this has caused problems in various waters around the world. Part of the nitrogen and phosphorus leachate comes from manure ‘run off’ from the intensive cattle farming. There is just too much manure in one place to deal with in the traditional way of composting and again the soil can’t retain the liquid element of it.
So where does that leave animal manure and the home gardener? Is there a need to add to your carbon footprint by travelling to collect animal manure, or can you generate sufficient nitrogen without it?
You don’t need animal manure to make compost but it will help speed the composting process if you do have it. There are other substances rich in nitrogen that can do the job although generally you need more of them to add the same amount of nitrogen. Nettles, comfrey and seaweed all have a good nitrogen content with comfrey (C:N ratio 10:1) rivaling farmyard manure (14:1). The lower the ratio, the more nitrogen-rich the substance will be. Chicken and bat (guano) dung are the best manure sources of nitrogen (around 7:1) with cow, horse and pig being more balanced and nearer the ideal for composting of 25 to 30:1.
Much of the waste generated in a garden (prunings, flower stems, etc) has a higher carbon content, which slows down the composting process. To make a finished compost with a high nitrogen content it will need to have a high nitrogen input. Grass mowings and any other soft leafy growth will be higher in nitrogen and as long as they are mixed with substances with more structure and therefore carbon, they won’t collapse into a dark, smelly mass. If they do this, the smell of ammonia indicates that your valuable nitrogen is being released into the air and will be lost to the land.
Seaweed contains a huge range of micro-nutrients and it’s great to compost as it breaks down quickly and speeds things up. However, a glaring drawback, chances are it isn’t going to be growing in your garden either!
Comfrey and nettles on the other hand are more likely to be present, or can easily be grown. ‘Bocking 14’ is the comfrey favoured by Henry Doubleday who conducted many trials in the 1950s. The main feature of Bocking 14 is it doesn’t readily set seed so won’t spread to where it isn’t welcome. Other varieties are fine to use if you have them already just not quite as rich in nitrogen. Nettles can be harvested before they set seed, when they first start to flower or before is probably the best time. Cut them down to the ground and place in a compost bin or they can be steeped in water to make a liquid feed perhaps for hungry tomatoes or other vegetables. This is one of the smelliest concoctions you will ever make but that smell may provide a deterrent to insect pests. Their sense of smell is a good deal more acute than ours and when we don’t notice the stink after 48-hours they can still detect it for substantially longer.
Comfrey and nettles will use nutrients in order to make their leaves which will then have to be replenished to keep fertility levels up. Equally domestic animals have to be fed plant material to live and produce their manure. A way of increasing nitrogen without using any existing stores is by growing certain green manures. Green manures come in many shapes and sizes and generally are grown directly on the soil you wish to feed. Some of these are nitrogen fixers such as the legumes alfalfa and clover. Nitrogen fixing plants, of which there are relatively few species, use bacteria which take nitrogen from the air and store it in nodules on the plant roots. The top of such plants can be harvested before flowering and the roots dug into the soil to add fibre and structure as well as the nitrogen.
Herbivore manure provides a better source of nitrogen than any non-animal alternative but by using plants such as prolific nettles and comfrey, and green manures, fertility can be maintained to an extent. It depends how productive you want your land to be. If you want to grow annual food crops on a reasonably large scale (i.e. allotment size) some form of domestic animal: cows, horses, chickens or pigs, will be necessary if fertility is to be retained over time. Even roses require more than average food to really thrive. Growing native perennial plants that are suited to your climate however, requires little more than the soil provides and by supplying compost made from your garden’s own prunings and debris there will be sufficient nutrition to keep everything healthy. The principle of forest gardening takes this a step further by selecting plants for the garden, especially shrubs and trees, that are productive but also native to hedgerows.