Monitoring your crops is important for a healthy crop. To prevent bacterial and fungal diseases, keep the mulch around the plant light and airy.
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Green onion plants grow quickly, so it's important to stay on top of them: they'll get tall and much thicker in about a month. Give them a dose of fertilizer to help them along. Once the roots are established, they'll grow much more quickly. Once the fertilizer is applied, pile mulch around the stems of the plants. The most tender and tasty part of a leek is the white part on the bottom, and by keeping the stems covered it'll help them stay white. The sun is what makes them turn green and fibrous.
Keeping the stems white, also know as blanching, can help you get a much better crop of leeks. You can double the amount of white stem by keeping them covered. Be sure that the air circulation around the plants isn't completely cut off, or they could rot. Using a lightweight mulch helps to avoid rot.
In addition to rot, all onions can get leaf blight and purple blotch diseases. Leaf blight is caused by a fungus that occurs during hot, damp weather. The leaves dot, sink and wilt, and eventually the plant dies. Purple blotch is caused by a different fungus, which leaves a purple sunken hole in the leaves before wilting all of the plant's stems. This fungus is also common in hot, wet weather.
There are several ways to prevent fungus:
1. Pull out any sick plants immediately and throw them in the garbage.
2. Try not to water the leaves, only the soil. Fungus and bacterial both grow on damp foliage.
3. Make sure the mulch around the onions isn't too heavy and holding water. You can flip or fluff the mulch after rainy periods to keep moisture away from the plant stems.
Onions don't have many pests because of their strong flavor, but onion thrips are a real problem. Thrips are little yellow bugs, only 2mm long, that attack crops in June and can produce several generations in a single summer. Because they hide in and under foliage, they can do a lot of damage before they're noticed. Check onion plants carefully each week for signs of pests, destroying any you find either by hand or with an insecticidal soap to keep them away from the crop.
Within a month scallions can start to mature. The bulb should be about the same width as the stem; this is how you can tell scallions from other onions. To harvest, gently lift and wiggle them out of the dirt. Try not to disturb the other scallions nearby when you do this.
Chives are also easy to harvest; simply cut them as you need them once the plants are established and spreading. You can tell they're ready when they start to look like clumps of soft grass. Use a pair of clean scissors to clip just the number of chives you'll use within a day or two. Chives are almost always used fresh or raw because they lose their flavor if they're cooked or left in the refrigerator too long. Be careful to leave some of the stems on the plant; otherwise it might not be able to recover from its trim.
Garlic, or Chinese, chives also grow quickly and well. The edible buds are considered one of the best parts of the plant. Be sure to toss the stems and buds into a salad: you'll be surprised how fresh they taste.
Leeks take longer than the other green onions: it may be four to six months before they're mature. Once they're large enough for your taste, you can begin to harvest them. Pull them out of the garden just as you need them; the ones you leave will stay fresh in the ground as long as the temperatures are cool. Try not to damage nearby plants as you harvest; any cuts or bruises could be an opening for pests or infections. You can leave some of the plants to go to self-seed if you like; when you do this, the seeds may end up being scattered rather than in neat rows, but it saves money and time next year.
There aren't many crops you can pick whenever you want, and that's part of what makes growing these leeks, as well as the scallions and chives, so worthwhile. Don't forget that you can grow these in a container if you have limited space. Chives actually do well indoors, so put some in a pot and bring them inside for a taste of spring in the winter.