The United States Department of Agriculture (USDA) Plant Hardiness Zone 7 stretches across the United States from coastal New England to Oregon and Washington. It dips as far south as Arkansas, Texas and New Mexico. It is divided into two subzones, 7a and 7b. Average minimum temperatures in 7a are from 0 degrees Fahrenheit to 5 F, while 7b sees 5 F to 10 F. Bear in mind that these are average minimum temperatures, so it is possible to get lower temperatures occasionally.
The Right Temperature
Gardeners in Zone 7a have the best of both warm and cool climates. Summer temperatures are warm enough to grow tomatoes, peppers, eggplant and many other subtropical plants. Winter temperatures can be cool enough to freeze the soil several inches deep for brief periods, but moderate enough that a little insulation will protect plants from damage.
Spring planting of vegetable crops should be guided by your last average frost date. If you are unsure of this, ask the local County Cooperative Extension office, listed in the phone book. Seed packet instructions often contain statements such as "Plant seeds indoors six weeks before the last average frost," or "Sow seeds in the garden two weeks after the last average frost date."
Early spring is a good time to get Zone 7a soil tested. Wait until the soil is no longer frozen and has dried out a little. Contact your Cooperative Extension office for instructions on how to take a soil sample. The results of this laboratory test will contain instructions on which soil nutrients are in adequate supply and which need to be boosted with amendments. These instructions are typically based on so many pounds of amendment per 100 square feet.
Add the recommended soil amendments and lightly incorporate them into the top few inches of the soil with a garden fork or three-tine cultivator. Do not dig them in too deep, or they will be beyond the reach of plant roots. Wait for at least one week before sowing seeds or transplanting into the amended soil. This allows time for the amendments to be absorbed and take effect.
Preparing for Winter
When vegetable crops are finished in late fall, add compost and composted manure to the soil. These will increase the soil's vegetative content, which will help it to retain moisture and plant nutrients. Sow a winter cover crop, such as rye, oats, vetch, or peas, to prevent soil erosion by winter winds and rainstorms.
Winter cover crops should be dug or tilled into the soil in early spring. Try to time this process to coincide with the addition of soil amendments as recommended by the laboratory soil test.
Look for microclimates in your garden---small areas that maintain slightly higher temperatures than the rest of your garden. This is where to plant things such as rosemary that otherwise would have to be brought indoors over the winter.
The moderate conditions in Zone 7a allow a wide variety of crops to be grown, including tomato, chili pepper, sweet pepper, basil, carrot, lettuce, roses, peas and beans, radish and cucumber. Many perennial herbs do well in Zone 7a, including sage, thyme, oregano, sweet marjoram and mint. With a little protection, rosemary and lavender can be overwintered.