If there are any cool season vegetables left in the garden, they should probably be harvested pretty soon. If left too much longer, they will be ruined by warming weather. Cabbage will bolt (start to bloom) once it realizes that it is spring. Cauliflower and broccoli, which are juvenile flowers, will become bitter as the flowers mature and try to bloom. Besides, they all need to get out of the way.
Warm season vegetables need the space. Tomato, pepper, eggplant, zucchini and other squash plants are ready to disperse their roots and get to growing. They are usually planted as seedlings because only a few of each are needed. A few seedlings of each type are more reliable, but not much more expensive than a packet of seeds; and they do not need to take the time to germinate.
However, because they are so easy to grow, seed for zucchini and other squash, as well as melon, are popularly sown directly where plants are desired. There was no need to sow them indoors earlier to plant in the garden as seedlings now. Onions can be grown from seed for late harvest, or they can be grown from juvenile onions known as ‘sets’ for earlier harvest or for green onions.
There are two main reasons why cucumbers, beans and corn should be grown from seed, although cucumber seedlings can be practical if only a few are desired. Otherwise, so many individual plants are needed that it would be relatively expensive to purchase enough seedlings. The main reason for sowing seed directly is that their seedlings are sensitive to the stress of transplanting.
Tomato, zucchini and beans are likely the most popular of warm season vegetables because they are so productive and reliable, even in limited space. Pole beans can be grown on trellises against fences or walls in very tight spots. Corn is less popular because it needs so much space, and needs to be watered so regularly. Too few plants may not be adequate for cross pollination. Pepper and eggplant, as well as okra, are not too demanding, but appreciate rich soil, regular watering and warm exposure.