Optimum monthly average temperatures for plant growth are 60 to 65 degrees F. Collards will withstand a greater range of temperature, both heat and cold, than most other leafy vegetables. If the temperature decreases gradually over a period of several days, collards can withstand temperatures as low as 15 degrees F. Collards may be seeded directly into the garden or transplanted. Collards may be harvested by three general methods or a combination of the three. The entire young plant can be cut off at ground level, just as mustard greens are, the entire mature plant can be cut off at the ground, or the bottom leaves can be stripped off the plant periodically, leaving the bud to grow and produce more leaves. Collards tend to improve in flavor as the weather turns cooler in the fall.
Leaves remain tender and edible for several weeks after reaching maturity.
Kale Kale is a member of the cabbage family and is grown for its succulent leaves and stems. A hardy vegetable, kale can be overwintered in Delaware. Culture of kale is much the same as for collards. Kale may be harvested in one of two ways. The entire young plants can be cut off at ground level about 40 days after seeding.