We have an area that we attempt to use for gardening every year. It makes a nice garden area of about 10 feet wide by 20 feet deep. It will probably end up being the subject of several questions. But the first is how to clean it out and prepare it for spring? We are in northern California, USA (Zone 9) so it is hard to do anything with the area through the rainy winter. So the area is poorly cared for and horribly overgrown each year. What is the best way to eliminate the weeds and prepare the soil for spring planting?
I have converted parts of my backyard from lush lawn to lush vegetable patch. Here is what I tried in ascending order of work involved. The first two are the approaches that have given me good results so far.
I would recommend against herbicides to get rid of the grass and weeds, especially if you are going to use this patch for vegetable gardening. If you keep on top of the weeds on a regular basis, say every weekend, it won't be too much work.
Note: I live in Southern Ontario with hardiness zone 6a-5b, where we have snowy winters. The best approach might be different for your location, where I imagine things grow all year long.
It sounds like you have a mature garden space, and the problem you're facing is weed control.
See my answer to another question on weed control for a general approach, mainly:
This will work (somewhat) to keep the milkweed at bay, though you may have a similar problem to that mentioned in the linked question: seed blowing in from outside your property.
Aggressive grasses can be harder, especially if they spread by rhizome or stolon. You can try starting from a fresh slate by covering the area with heavy black plastic for two weeks. This will block out light, and if it is sunny, should cook the weeds. Some weeds are really aggressive, and will survive this kind of treatment. Rototill. Rake the garden smooth. Wait a week, then cultivate shallowly to kill anything that is resprouting. Repeat for a couple more weeks; this should reduce the amount of weed seeds that are ready on the surface to germinate.
Plant your vegetables into the garden.
Cultivate regularly during the growing season. Shallow hoeing, once a week, will keep the weeds down. If you still have aggressive grassy weeds, you may need to hand pull and/or cultivate more often. Be persistent, the effort will pay off in the long run. (At least I hope so! I started a battle with some aggressive grasses last year, I hope to start this spring with the upper hand...)
In the fall as you remove vegetables following harvests, plant a thick cover crop. You want something that grows well in your area, germinates quickly, is winter hardy (in zone 9 this won't be a problem), and will grow so thickly that weeds can't catch hold. For me, this is winter rye; if this grows well where you are then you can use it, otherwise you'll need to find something that suits your environment. The following spring, till it in before it puts on too much growth, and wait a couple of weeks before planting (especially with rye, which gives off a natural chemical that prevents seed germination).
Continue annually with regular cultivation and thick winter cover crops, and you can keep weed pressure to a minimum. As a bonus, the cover crops will help improve your soil.
Good hygiene in other parts of your yard is helpful too: if you let milkweed grow along your back fence, it's going to spread seeds into your garden. Same for the grasses in your lawn. If you need help controlling weeds in your lawn, so that they won't spread into your vegetable garden, see this answer.