It’s the middle of April and its still quite cold, it’s not yet warm enough to transplant the seedlings grown at home nor for direct sowings. I have been slowly uncovering my beds, lilting the cardboard coverings and despatching the slugs, spot weeding of couch grass and ground elder. I set up beer traps on the beds I plan to sow in the next couple if week. I have been emptying all my ready compost bins onto the beds. I never have enough compost and I tend to use green manures whenever possible; those that were grown in late summer / early autumn were covered in cardboard when the frosts came and the plants died back. Now I lift the cardboard and clear any stems that haven’t been taken into the soil into the compost bins. I am thinking of using summer green manures this year, sowing soon to give the soil a boost on some beds where I can plant my beans and corn through it in a couple of months.
If you have never used green manures, here is some information on why to consider using them.
1. Plants need a wide range of nutrients to grow well – the 3 key nutrients from the soil are nitrogen phosphorous and potassium and carbon, oxygen and hydrogen from the air; other soil nutrients required are magnesium, calcium and sulphur. We add fertilisers to boost growth and improve flowering / fruiting, but synthetic fertilisers reduce the fertility of the soil in the long run as they disrupt and kill off the microbes that keep your soil healthy
2. Green manures area plant based alternative to animal manures. Sown as seed on bare ground and grown to cover bare soil often once a crop has been harvested or to fill gaps between plants or to under plant taller crop. They can be used as a filler crop to keep soil covered before a main crop as well as afterwards. They are quick growing and have deep roots which bring nutrients to the surface and thus available to future crops. They stop nutrients being washed out of the soil by the winter rains and prevent soil compacting. When they are dug back on they release nutrients back to the soil. Green manures help create healthy soils which are full of invertebrates, bacteria and fungi which break down organic dead matter (manures and dead plants) and make nutrients available to the growing plants
3. There are summer grown manures which form dense foliage and act as a weed suppressant (buckwheat and fenugreek) as well as autumn soil which will stay over winter. There are many different types and you need to choose which ones are best for your plot – thinking about the soil, the space available at any given time, crop rotation and what you want to grow next. There are some good guides on the web, try RHS.org.uk, gardenersworld.com and greenmanure.co.uk
I tend to grow those which will go in as beds are cleared of crops from August; the mustards and phacelia will soon be tall and I leave to flower for insects and bees in the autumn. Some will stand all winter; others will die back when the frosts come and I cover with cardboard and let rot into the soil over winter. If you dig then you can dig the green manures into the top 25cm of soil.
4. How to sow. I broadcast and rake into the top of the soil; you can sow in rows. You might want to protect from birds until the seeds sprout – especially is using the grazing ryes.
5. useful tips;
if you are digging the green manure in, its best to do it 2-3 weeks before planting crops or 4 weeks before sowing seeds – to give it time to rot down. Cut the green manure crop, leave if for a few days on the surface to wilt and then dig in. if the foliage is too tough and coarse to easily dig in its best to compost.
Ideally you want to cut back green manures when they are about to flower so as to avoid them dropping their seeds and growing a new crop that you might not want – unless you are leaving them for late pollinators. Personally I have never found this a problem – give me clover or mustard any day than couch grass and ground elder!
Benefits of using green manure
- Lots of leafy green manure vegetation helps increase the organic content of the soil – and it’s better than horse manure if you don’t know where it has come from or what’s in it.
- Green manures can either add nitrogen to the soil or it can lift it closer to the surface so boosting crop growth
- It prevents leaching of nutrients from the soil in the winter rains
- It provides cover for frogs, beetles and other natural predators that feed on pests such as snails/ slugs and can deter some crop pests such as carrot fly and wireworm
- It means you don’t have to weed.