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lupinGreetings, fellow gardeners – from the big smoke! I've left garden and animals in the care of my husband for a few days (I hope he remembers to top-up the slug bait on the daikon radishes) and I'm having a ball, jogging round the streets, poking my nose over fences to gawp at backyard city gardens. Gosh, we have it lucky it the country. I've seen so many hungry vegetable plants this week that I want to gather them all up and take them home with me – though I have the distinct feeling I'd be arrested if I started doing that! But honestly, I've never seen so many nitrogen-starved greens in all my life. It makes sense, of course. Most people are trying to grow organically these days and animal manure, the chief source of nitrogen, isn't exactly readily available in the city.

I've been thinking a lot about what I would do if I didn't have ready access to animal manure, and the answer I've come up with, though not new, is so novel to rural-old-me that as soon as I get back home, I'm going to experiment with it in a least one raised bed. Even though my donkeys and chooks are happy to supply all the manure I need, I'm going to try conjuring nitrogen out of thin air! To do this, I'll be sowing what is traditionally called a "green-manure crop". The other name for this autumn-sown seed is "catch-crop" and it, quite literally, catches nitrogen out of the air and delivers it to the plants' roots (isn't nature amazing!). Not all green-manure crops do this, of course. Some en-mass autumn sowings have a different purpose such as helping to reduce soil compaction and leaching during the fierce cold, wet months. But the crops I'll be using are the nitrogen-fixers, the most common of which are peas, broadbeans, and lupin.

I'll sow the seed thickly, and let the crop grow through the cold months. Come late winter or very early spring, before they plants have had time to set seed (I don't want them popping up everywhere once I've finished with them), I'll cut them down with the hedge clippers, chop them up with a spade, and dig them, nitrogen-covered roots and all, into the soil. As well as turning in all that free nitrogen, I'll also be supplying my soil with some delicious organic matter that will encourage worms. A couple of weeks later, and with a covering of compost added to the bed, the ground will be ready to receive its first sowing or planting of the season.

Sounds simple – and exciting! However I do have just one word of warning. If you're after organic matter only (and not so worried about catching nitrogen) you can sow a range of other green-manure crops, including several from the brassica family (the most common of these are mustard and radish). But if you have a clubroot problem in your garden, or if you want to plant vegetables from the brassica family (cauli, cabbage, broccoli etc) on the same spot immediately after digging in your greens, choose a non-brassica green-manure crop. That's because brassica should always be followed by a non-brassica crop to help deter clubroot or, if you already have the disease in your soil, to help eradicate it.

That's all for this week. I'm off for a run to the nearest garden centre to pick up a big bag of lupin seed. Over and out from the big smoke!

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