One of my first lessons in growing vegetables and herbs is learning the plant’s preference for temperature. To keep it simple, there are cool season and warm season crops. Getting to know what the plant prefers determines when to buy/plant, what to buy/plant, where to buy/plant, and when to harvest/eat!
In the mid-Atlantic area, typical cool season plants are anything in the cabbage family (cabbage, broccoli, collard, Brussels sprout), lettuce, pea, kale, chervil, dill, cilantro, leek, scallions, radish, spinach, arugula, beet, pak choi or bok choy, carrot, mustard, parsnip, turnip, and Swiss chard.
Some can continue to grow well during the summer such as spring onions and Swiss chard. Other cool season lovers “bolt” when it warms up in May/June. For example, cilantro will bolt, that is, flower and set seed, in May. This is good if you want the seed, also known as coriander, but bad if you want to continue to harvest the leaves. When the plant bolts, the leaves become bitter and eventually the plant will die because it is an annual.
Most people associate the warm season edibles with summer itself. These include tomato, basil, fennel, eggplant, pepper, corn, summer/winter squash, zucchini, melon, watermelon, cucumber, okra, and pumpkins. These will not tolerate the frosts we may get in the spring evenings so it is best to start them outdoors after the last average frost date in mid-May.
Frequently you will see both types of plants for sale as early as March. These photos were take at a local hardware store in March last year. Basil, a summer lover, is especially sensitive to cold. If one were to purchase these basil plants and put them in the garden unprotected they may die because there is still the likelihood of frost in early spring.
In my zone 7 garden, the cool season plants/seeds should be started outside in mid-March to the beginning of April. The warm season plants/seeds should be started in early May to the end of May. If you do not know what your vegetable or herb prefers, there are several ways to figure this out:
Read the seed packet or label
Read seed catalogs
Research on the internet
Read local gardening books
Visit garden nurseries and ask knowledgeable staff.
The books I found most useful books for this area are listed below and are easy to get from the library or bookstore. Knowing the plant’s preference will help you figure out when to start your seed and/or when to purchase plants.
The Week-by-Week Vegetable Gardener’s Handbook by Ron Kujawski & Jennifer Kujawski (Storey Publishing, 2010)
The Timber Press Guide to Vegetable Gardening in the Southeast by Ira Wallace (of Southern Exposure Seed Exchange) (Timber Press, 2013)
The Year Round Vegetable Gardener by Niki Jabbour (Storey Publishing, 2011)
Gardening in the Mid-Atlantic, Month-by Month by Andre and Mark Viette with Jacqueline Heriteau (Cool Springs Press, 2008)