When feeding the garden it’s best to use natural fertilisers, such as manures, blood & bone, fish emulsion or blended organic fertilisers. No matter what kind of fertiliser we choose to use, it’s important to apply the right amount, and no more! For plants, over-fertilising is as bad as under-fertilising, and for gardeners, using more fertiliser than necessary is costly and wasteful.
How do we know how much fertiliser to use?
The product label of every commercial fertiliser list the application rate, how much to use per specified area, and also the application frequency, when and how often the product should be applied to the garden.
How Much Manure Do I Need to Feed the Garden?
Non-commercial fertilisers, such as bags of cow and sheep manure usually don’t specify application rates.
Cow or sheep manure is a fairly mild fertiliser, apply 2-4 litres per square metre (2-4L/m²) of garden bed, or 0.5-1.0 gallon per square yard (gal/yd²) in imperial measurements.
Tip: A regular household bucket holds 9 litres (2 gallons), so a bucketful of cow or sheep can be applied over an area of around 2.5-4.5 square metres (2.5-4.5m²), or approximately 2.5-4.5 square yards (2.5-4.5 yd²) and dug into the soil.
Chicken manure is a much stronger fertiliser, so it’s applied in smaller amounts, but more frequently. Apply around 150g per square metre (150g/m²), or 5 oz per square yard (5 oz/yd²) in imperial measurements, prior to planting, and then apply 100g per square metre (100g/m²), or 3.5oz per square yard (3.5 oz/yd²), every 8-10 weeks during the growth period if desired.
Keep in mind that chicken manure releases its nutrients faster than other manures, and only lasts around 6 months in the soil.
Sheep and cow manure, which are much milder manures, release their nutrients more slowly over a 12-month period.
How Often Should Manure Be Applied to The Garden?
At the very minimum, a garden should be fed with fertiliser twice a year:
- Once at the start of spring (September in the southern hemisphere, March in the northern hemisphere) for the warm season crops
- Then again at the start of autumn (March in the southern hemisphere, September in the northern hemisphere) for the cool season crops.
The garden can be fertilised more often though, as often as every 8-weeks (2 months), between spring and autumn.
In temperate climates, gardens should not be fertilised after the start of autumn. When the weather cools down, soil temperatures drop and the soil nutrient nitrogen, which is responsible for leafy green growth of plants, becomes unavailable for plant uptake.
Would you treat horse manure the same as cow or sheep manure?
Yes, you can use horse manure the same way as cow and sheep manure, it’s a bit richer though.
Don’t use fresh horse manure in the garden, all animal manures need to be composted for around three months before they can be used in the garden. The bagged and bulk manure products sold at garden centres are already composted, so they can be used in the garden immediately.
Hi Angelo
I always love your blog posts, and read them religiously.
As a permaculturalist though, how do you add manure without disturbing the soil? Do you just plonk it on top of what is already there, and do you scrape the mulch off to get to the soil to do this?
I would be super intrigued to know.
All the best, Jill (insta@ carrots_and_kale_from_the_vale)
On Fri, 17 Sept 2021 at 14:24, Deep Green Permaculture wrote:
> Angelo (admin) posted: ” When feeding the garden its best to use natural > fertilisers, such as manures, blood & bone, fish emulsion or blended > organic fertilisers. No matter what kind of fertiliser we choose to use, > its important to apply the right amount, and no more! For” >
Thanks Jill, appreciate the great feedback!
When adding manures or other fertilisers to the garden, it;s important to incorporate them into the soil, that is, dig them in, so the nitrogen isn’t lost by volatising into the atmosphere.
That said, the best way to add manure to a garden without disturbing the soil is by using the system of no-dig gardening.
All I do to fat the end of each season to feed my garden is:
1. chop & drop and plants that are finished for the season
2. add any mulched fruit tree prunings if available at that time of year
3. add any compost or worm castings that may be ready to use
4. sprinkle the manure over these materials
5. cover the whole lot with a straw mulch such as lucerne, peastraw, sugar cane mulch
This chop and drop technique is also known as sheet composting, it’s fast, efficient, and doesn’t disturb the soil, because there’s no digging involved!
It’s worth a try, I’ve been doing this for over a decade now, and have never looked back, the soil transformation that has occurred is incredible.
You say that nitrogen becomes unavailable during winter in temperate regions. Why is this? I always thought that plant growth stopped because of the cooler weather and less sunlight, not because of a lack of nitrogen. Then, because plant growth has slowed or stopped, adding nitrogen fertiliser is not needed as it will only be washed away.
Thanks for an excellent question!
Remember that plants can still grow with less light, see my article How Much Sun Do Vegetables and Herbs Need to Grow?, though some respond to day length.
The reason why we don’t fertilise in cold weather in temperate climates is because the low soil temperatures reduce soil microbe activity. Just like most living things, the microorganisms in the soil are more active when its warm, and less active when its cold.
Microbe activity plays an important role in several key parts of the nitrogen cycle, and the two that are important here are the processes of mineralisation and nitrification.
Mineralisation is the process whereby microbes decompose organic nitrogen (N) from manure, plant materials and soil organic matter into inorganic forms, first to ammonia (NH3), and then to ammonium (NH4+). This occurs most readily in warm, well-aerated, moist soils with a temperature of 20-35C (68-95F),
Nitrification is the process whereby microorganisms convert ammonium (NH3) to nitrite (NO2-) and then nitrate (NO3-) in order to obtain energy. This occurs most readily in warm, well-aerated, moist soils with a temperature of 19.5 – 30C (67-86F), but virtually halts below 5C (41F) and above 50C (122F).
The process of conversion of nitrogen from organic matter to nitrate which plants can use is as follows:
R-NH2 -> (NH3) -> (NH4+) -> (NO2-) -> (NO3-)
organic N ammonia ammonium nitrite nitrate
Nitrate (NO3-) is the form of nitrogen that is most available to plant, and that plants use the most. It’s also water soluble and therefore highly susceptible to leaching out of soils. For these reasons we need to replenish the soil nitrogen.
That’s a very comprehensive answer. Thank you. One more question… Mineralisation and nitrification slow down or stop altogether at low temperatures, limiting the amount of nitrogen available to plants, but what happens if you give them a fertiliser that is not dependent on microbial activity? I think that Urea ((NH2)2CO) hydrolyses in water to give NH4+, NH3, CO2 and a OH- ion. Would this have an impact on plant growth? Or is it more likely to be washed away?
You’re welcome! I’ve gone one better and have published an article on the topic – Why You Shouldnt Fertilise Gardens in Winter in Cool and Temperate Climates.
To answer your question, urea isn’t just a synthetic fertiliser, it’s also a component of natural fertilisers. The reason poultry manures release their nitrogen the fastest, with 90% of the nitrogen released in the first year, is because most of it is the form of urea or uric acid.
Urea only hydrolyses in water with the enzyme urease present, forming ammonia with carbamic acid as an intermediary, which then rapidly decomposes to ammonia and carbon dioxide. If the ammonia gas interacts with water in will form ammonium.
The ureolytic soil microbes are the major producers of the urease enzyme, which hydrolyzes urea into ammonia and carbon dioxide.
Plants can use some ammonium, but take most of their nitrogen in the form of nitrate, so the process of nitrification still needs to take place to convert ammonia into ammonium.
The fertiliser that is not dependent on microbial activity is the end product of nitrification, and that’s nitrate. Since nitrate fertilisers are water soluble, and they don’t slowly release over 12 months or more like organic nitrogen fertilisers, and are very prone to leach out, causing groundwater contamination and eutrophication of waterways and aquatic environments.
Ever seen pictures of lakes the colour of pea soup with all the dead fish floating at the top, that’s caused by runoff of nitrate fertilisers from farms causing explosions of growth of algae which suffocate aquatic environments. When synthetic nitrate fertilisers are used on plants, all of it is available all at once, so plants are force fed nitrogen when they only need to take up water. This results in soft, sappy growth with long internodes, creating weak pants that are very attractive to pests, and hence more vulnerable to pest attack.