It seems to be much too early for cool season vegetables while the weather is still so warm. Summer vegetables, which are also known as warm season vegetables, are still at their best. Most will continue perhaps until frost. Yet, months ago, they also started prior to their growing season. At that time, cool season vegetables, which are also known as winter vegetables, were still producing.
Although it really is too early for winter vegetables to grow in the garden, it is time to plan for them. Those of us who prefer to grow varieties of winter vegetables that are not likely to be available in nurseries should get their seed now. In only a few weeks, it will be time to sow the first phase of seed for carrots and beets directly into the garden. By October, it will be time to sow seed for peas.
Broccoli grows slowly from seed. Whether it goes directly into the garden, or into flats for later transplant, broccoli seed should get sown by about now. If the preferred gardening style allows for it, seed for winter vegetables can be sown below old summer vegetable plants. The seed for winter vegetables can germinate and start to grow as summer vegetables finish and vacate the garden.
Cauliflower and cabbage seed want to germinate and start growing shortly after broccoli, within the next few weeks. However, seedlings of the more popular varieties of cauliflower and cabbage, as well as broccoli, will be available in nurseries for later planting. Lettuce, spinach and kale do well from late seedlings, or seed sown after cauliflower and cabbage, along with carrots and beets.
Root vegetables, like carrot, beet, radish, turnip, rutabaga and parsnip, grow from seed, sown directly.
Eventually, some of the warm season or summer vegetables will need to relinquish their space to winter vegetables. Most will finish by that time anyway. Those that stay long enough will succumb to frost. Summer vegetables can stay latest where subsequent phases of winter vegetables will later (not yet) replace an early phase. Subsequent phases begin production as early phases finish.