Green Manure & Cover Crop Selector

Free Green Manure & Cover Crop Selector — Find the Right Crop for Your Bed

Leaving a bed bare between crops is one of the most common missed opportunities on the allotment. Bare soil loses nutrients through leaching, compacts under rainfall, dries out in summer, and gives weeds a free run. A cover crop or green manure fixes all of that — and often improves your soil significantly in the process. The question is which one to sow, and when.

Our free Green Manure and Cover Crop Selector takes the guesswork out of it. Tell us when your bed is free, when your next crop goes in, and what your soil needs most — and we'll recommend the best options ranked by how well they match your situation.

How the Selector Works

Not all cover crops suit all situations. Phacelia is brilliant in summer but won't survive a hard winter. Grazing rye is the go-to for overwintering but needs at least 16 weeks to do its job. Winter field beans fix nitrogen and break compaction but need to go in by November. Our selector filters the full range by your timing window first, then ranks what's left by how well each crop addresses your specific soil needs.

• Sowing month — when the bed becomes available, from January through to December
• Time until next crop — how many weeks or months you have before the bed is needed again, from 2 months up to next year
• Your soil needs — boost nitrogen, break compaction, suppress weeds, prevent erosion, attract pollinators, or add organic matter. Select as many as apply

The selector then shows you up to four recommended cover crops in order of match score, with the best fit highlighted. Each result includes a description, the specific benefits it delivers, when to sow it, how long it needs, and a link to buy seeds.

What Each Cover Crop Does

Nitrogen fixers

Leguminous cover crops — clovers, vetches and field beans — host nitrogen-fixing bacteria in nodules on their roots. These bacteria pull nitrogen from the air and convert it into a form plants can use. When you dig the crop in, that nitrogen is released into the soil over the following weeks, effectively giving your next crop a free feed. This is particularly valuable before hungry crops like brassicas, sweetcorn and leeks.

Weed suppressors

Dense, fast-establishing cover crops like mustard and phacelia outcompete weeds by shading the soil surface. This is especially useful on beds that have a weed problem or that you can't attend to regularly. A good cover crop can significantly reduce your weeding workload the following season.

Soil improvers

All cover crops add organic matter when dug in, but some are more effective than others. Grazing rye and rye-vetch mixes produce large amounts of biomass and have extensive root systems that improve soil structure significantly. Winter crops left in over several months can make a dramatic difference to heavy or compacted soils.

Wildlife and pollinator crops

Phacelia, clovers and buckwheat are among the best flowering cover crops for beneficial insects. Phacelia in particular is rated as one of the top bee-attracting plants you can grow, producing abundant nectar over a long period. If you have an empty summer bed, a patch of phacelia does more for your plot's biodiversity than almost anything else you could sow.

Tips for Getting the Most From Your Cover Crop

• Dig in before it sets seed — this is the most important rule. Most cover crops become difficult to control and may self-seed prolifically if left to flower and set seed. Cut or dig in as soon as flowering begins
• Allow 2–3 weeks before planting — freshly dug-in green manure needs time to break down before you plant into it. Allow at least two weeks, ideally three, between digging in and sowing or transplanting
• Water after digging in — moisture accelerates decomposition. If conditions are dry after digging in your cover crop, watering the bed will speed up the breakdown significantly
• Mix it up — different cover crops fix different problems. Alternating nitrogen-fixing clovers with deep-rooting ryes over successive seasons builds soil health more effectively than using the same crop every time
• Don't leave it too late — most cover crops need at least 6 weeks to establish before they provide any real benefit. If your window is shorter than that, simply covering the bed with cardboard is often a better option than a rushed sowing