One of the most common mistakes made by beginning vegetable gardeners is harvesting the crop at the wrong time. Since ripeness varies according to planting time, the weather in any given year, the variety of the particular vegetable planted, and many other things, one can't just say, "Harvest this vegetable on August 20th." So we've gotten together a general guide for harvesting many commonly-grown vegetables.
We thought of restricting it to vegetables that grow easily here, or to summer harvest only--but greenhouse-growing is becoming more popular so we decided to do the long list.
Beets: You can harvest and eat the green tops that you thin out of the rows. Beets are somewhat a matter of preference when it comes to the right size. Most prefer a diameter of 1.5 to 2 inches, but they are ready any time after the shoulders come above the soil line.
Broccoli: We eat the unopened flower buds of broccoli, so check often as weather warms, and get them before they bloom (don't expect your heads to get to supermarket size). Harvest when the buds are about the size of a match head. Remove with a sharp knife; leave between 4 and 6 inches of stem.
Brussels Sprouts: Harvest when they are green, plump and firm (usually an inch or more in diameter). Harvest by twisting off or cutting the sprout from the stem.
Cabbage: Harvest cabbage when the head is firm and has reached adequate size, depending on the variety and growing conditions.
Carrots: Depending on variety, pull when about 3/4 to 1-1/2 inches in diameter. The top of the carrot will show at the soil line; you can gauge when the diameter looks right for your variety. If the diameter looks good, chances are the length is fine too.
Cauliflower: As with broccoli, your cauliflower heads will probably not get to supermarket size. Harvest when the head looks full and while the curds of the head are still smooth.
Chard (Swiss): Harvest as leaves become large enough.
Collards (kale and mustard): Harvest young plants or lower leaves on older plants. Leaves should be young and tender. Taste improves with cool weather.
Garlic: The garlic tops will fall over and begin to brown when the bulbs are ready. Dig gently, don't pull, and allow to dry before storing. Shake off dirt rather than washing.
Kohlrabi: For the best texture, harvest once the kohlrabi "bulb" is between two and three inches in diameter. Too much larger than that and it will be tough and woody.
Leeks: Harvest leeks when they are about 1 inch in diameter.
Lettuce (Head): Harvest once the head feels full and firm with a gentle squeeze. Hot weather will cause it to bolt or go to seed rather than filling out.
Lettuce (Leaf): Harvest the outer leaves once the plant has reached about 4 inches in height. Allow the younger, inner leaves to grow. Leaf lettuce can be harvested in this fashion for quite some time. If seed stalks begin to form, harvest the whole plant immediately and refrigerate.
Onions: Onions can be dug once at least half the tops have ripened and fallen over. Allow the onions to dry in the sun.
Onions (bunching): Dig before bulbing starts or before they become too thick (over 1/2 inch diameter).
Peas (English): The pea pods should look and feel full. Peas are sweeter if harvested before fully plumped. Peas really need to be tasted (raw) to determine if they are sweet enough.
Peas (edible pod): Harvest when the pods are fully developed, but before seeds are more than half size. (You'll need to develop a feel for this one.)
Radishes: Radishes mature quickly. Harvest as soon as they reach edible size. They will go quickly to seed.
Rutabagas: The bulbs should be about 3 inches in diameter. Rutabagas can be mulched, left in the ground and dug up as needed. Cold weather improves their flavor.
Spinach: Spinach goes to seed quickly. Harvest by cutting at the soil line before you see a flower stalk beginning to shoot up. Or cut just below the crown for a one-time harvest.