When should I plant green manure?

The best green manure planting time is whenever a bed would otherwise sit bare. Empty soil washes away in the rain and fills up with weeds. So you want a living crop holding that ground instead of nothing at all. The biggest window of the year comes in fall, when summer crops clear out and beds go quiet for months. That gap is a chance, not a loss, and a cover crop turns it into free soil building.

You will notice your beds emptying fast once the harvest ends. That bare ground in fall is the prime spot for an overwinter green manure. Sow a hardy crop in early fall and it covers the soil all winter long. It holds nutrients in place, shields the surface from heavy rain, and gives you a head start on spring. Crimson clover, hairy vetch, and winter rye all handle the cold well. Pick the one that fits your goal, then sow it thick so weeds get no room to move in.

Good fall cover crop timing means sowing while the soil is still warm enough for seeds to sprout fast. Aim for about a month before your first hard frost so roots can settle in. Wait too long and the seedlings stay tiny and weak through winter. Get them in on time and they bulk up before the cold, then take off again as the days warm. A few weeks early beats a few weeks late every single time.

Spring and summer gaps are your other chance to plant. Any bed sitting empty for a few weeks can grow a fast crop like field peas or buckwheat. Buckwheat sprouts in days and fills a short gap before it sets seed. Field peas add nitrogen while they grow and break down quick once dug in. Cut buckwheat back within a few weeks so it never drops seed and turns into a weed of its own.

Timing the dig-in matters as much as timing the sowing. Research in Frontiers in Plant Science studied hairy vetch and what happens after you cut it down. About 30 days after you terminate the crop, nearly all of its nitrogen releases into the soil. So work backward from your next crop. Dig the vetch in roughly a month before that crop most wants nitrogen. The supply then lines up with the demand, and far less of it leaks away.

As a rule, dig legumes in as they start to flower and cut rye when it reaches about 6 inches (15 centimeters) tall. Past those points the growth turns woody and ties up soil nitrogen instead of feeding it. After you dig any crop in, wait two to three weeks before you plant. That short pause lets the material break down first. Skip it and the rotting plants can rob your young seedlings of the very nitrogen you grew the crop to add.

So make this your plan. Sow an overwinter green manure in early fall on any bed the harvest has cleared, and use spring or summer gaps for quick crops. Then dig each one in before it flowers and give the soil a couple of weeks to settle. Get the timing right and you should never have bare ground losing nutrients to the rain. Your beds stay covered, your soil keeps building, and your next crop starts in better ground than it would have.

Read the full article: Green Manure: A Practical Soil Guide