The first between-row weeding should be done after the crops emerge from the soil, especially with carrots and other root crops, they do not like to be disturbed or buried when they are just emerging. I use a blade hoe and run down the rows, just to knock back the majority of the weeds, careful not to cultivate out the crops.
The first hand weeding should be done when the crops are established, and if the weed pressure is not too bad, wait until the root crops have their first true leaves. This bed of parsnips had some established grasses the previous year, so I did my best to cultivate out all of the rhizomes and established weeds like clover, daisy and chickweed, before planting. But there's always some left behind. I waited for a good rain to soften the soil and hand picked the grasses, pulling up rhizome and all. This is the only kind of hand weeding I do in wet soil, or on cloudy damp days.
In a well cultivated bed of humus rich, moist soil, you can sink your hand right down, next to the grass, and pull up the rhizome without disturbing the crop.
Collect the rhizomes in a bucket, or something similar, and remove them from the garden. If they are left on the pathways they will re-root themselves, at least in our climate, we don't get enough dry, hot days in a row to kill grass rhizomes. The annual weeds are still small and can wait a week or so before hand weeding, but the rhizomes were just beginning to establish themselves, and would have been more difficult to remove completely a week later. So I went through and quickly pulled all the rhizomes while they still come easily out of the soil. Weeding at the right time, saves time.
This bed of onions was picked for rhizomes a week earlier, and the between-row cultivation done just after emergence of the crop. It is time for hand-weeding the annuals, so I waited for a sunny, warm, windy day. Annual weeds will wilt and be killed by exposure to a few hours of hot sun, and will not be able to re-root themselves on the surface of dry soil. Also, if you pull annual weeds from wet soil, you will notice that the soil sticks to the root ball, potentially disturbing your crop. This will happen less in dry soil.
I work down one row at a time, using both hands, looking ahead for the next onion in the row, pulling weeds to either side around it, and clearing the weeds between the next onion "blind" while my eyes scan for the next onion... In this way, I can move down a row quickly, and make short work of a job usually done in the height of mosquito season.
While weeding, I kept noticing these cut onion stems. I couldn't think of a cut-worm that would bother onions, so I speculated that I had somehow sliced them in cultivation, or that they had gotten a light frost in emergence and the frosted part died back. But it certainly did look like cut-worm damage to me, as there would be many in a row cut, and then none. Then I started to find the culprits.
It's a little guy, only 1/2 inch long. Our usual cutworms are much bigger, June beetle larvae, and they would not bother with onions, going for the bigger stems like beans or tomato transplants. But again and again, when disturbing the soil around cut onions, I would find these small caterpillars. Fortunately, the onions mostly recover from the cut, unlike beans and tomatoes, so they only set the crop back a bit.
The only moth I can remember seeing in any number in the garden yet are these small iridescent purple moths. And while I was weeding, one flew right down at my feet, allowing me to get a good look at it. Still hunting down it's name.
Ed: The cutworm is of the family Lepidoptera Noctuinae, cutworm or Dart moths. The moth below is not the culprit after all, but instead a rather plain looking moth that we have just recently begun to see. The cutworm larvae overwinter in the soil, emerge in spring as cutworms, then transform into the first generation of adult moths of the season. They can produce up to 3 generations in our climate. Cultivating the garden in the fall will disturb the larvae, but would also disturb the beneficial insect larvae such as Soldier Beetles. Allowing the chickens into the fall garden would help reduce the numbers, but we would need a much larger flock of chickens to do the job properly in a garden our size. The most promising predator of the cutworm looks to be Beneficial Nematodes which infest and feed on cutworms, killing them within 2 days. They can be purchased and applied, but we are looking into the conditions required in the soil to encourage our own native beneficial Nematodes such as Steinernema carpocapsae and Steinernema feltiae. Beneficial Nematodes also prey upon Flea Beetles (among many other insects).