Cover Crop Legumes

When you're making a forest garden (or any productive garden for that matter), the success of the system is heavily dependent on how well you maintain soil fertility.

You've got to make up for the fact that you're going to be continually harvesting food (= soil-derived nutrients) from the land. In our case, working on a pretty impoverished piece of land, we're making this a very high priority. So I'm busy getting to know my legumes.

I've written about these a few times before, focusing mainly on white clover. Legumes are great for the soil as they team up with friendly bacteria to fix nitrogen from the atmosphere into the soil. Used as a chop and drop mulch, they're really good at building up organic matter and fertility for your soil.

My next trial will be of five species of legume commonly used as green manures for organic vegetable growing. These are all short-lived plants (mostly one season only), so can easily be replaced when I'm ready for it, by the cosmetic herbs or perennial vegetables that I've ultimately got planned to make up my forest garden understorey.

Over the next year, I'll be trying out crimson clover, agricultural lupins, trefoil, field beans and winter tares. I'll be testing them out in a couple of spots that I've had under a cardboard mulch this year.

Crimson clover is one that that grows through the summer - it can be sown from April until September and then you cut it back in autumn. It's vigorous and fast growing, so I've been sowing this one out this week and am hoping for some growth before I cut it back in the autumn.

The lupins are another one to sow in spring and cut back in autumn. They're deep rooting, so good for breaking and aerating the soil. We'll need a lot of that for any compacted soil we find under that concrete. I imagine these will be quite tall, so I'll need to be careful not to sow them too close to any of the fruit trees, fruit bushes and cosmetic herbs that I've got growing through my cardboard mulch.

Winter tares will last through the cold of the winter, but can be sown from as early as March, right up until September, making them look like they can be used either for summer and/or winter. These are basically a vetch and we've already got lots of that growing locally and on site, so it should do well.

Trefoil will also last through the winter, and will make fairly short plants, so they are going to be good options for sowing in amongst my existing plants and trees. This one gets sown anytime between March and August. Like the tares, we've already got birds foot and lesser trefoil growing on site, so it clearly likes our climate and soil type.

Lastly, field beans. These also grow through the winter (sow from September) and, like the lupins, are deep rooting so should join them in helping to break up any compacted soil. Again, like the lupins, I think these are going to be tall plants, so I'll need to be careful about where I put them.

Growing green manures is fairly new to me - I've tried it a couple of times, but both times when I was too busy to cut it down at the right time, so it grew too big and was then a pain to deal with. I'm hoping it works better for me this time around. Has anyone else had any experience with this? How did it work for you?