Weather plays a key role in when to plant a vegetable garden. It is imperative to determine the last frost date for the area so plants and seeds do not succumb to frost damage. Amazingly, planting can go on throughout the year because of warm weather vegetables and winter varieties that are harvested the following year. Garden preparations are also an ongoing task, from selecting seeds and starting them to developing a plant rotation system to keep the soil healthy.
Estimating Last Frost Date
Transplanted crops and warm weather vegetables are planted after the last expected frost date for the area. Determining the last frost date is not always easy. Weather conditions are constantly changing from season to season. Global warming has impacted seasonal temperatures and conditions over the past few years. The best way to know what time of year to plant a vegetable garden is to study the past frost dates of previous years and estimate when that time is for the current year. See Resources for a link to the National Climate Data Center. This site presents a list of the last known frost dates by state, with each state listing major cities, for the gardener to estimate the prime planting time of plants and seeds.
When to Start Seeds
Gardeners who grow their own plants from seed should start preparing at least four to six weeks before the last frost date for their area. The plants will have a chance to grow healthy and strong during this time. After the plants become are mature enough to be transplanted, a hardening off period is needed. To harden off the young plants, place them outdoors during warm weather for a few hours each day. Do not leave the tender seedlings in direct sunlight. Bring the plants inside any time there is a danger from cold or other weather conditions. Hardening off the plants will make them stronger and help them survive being transplanted into the vegetable garden.
Preparing the Garden
The soil should be tilled as soon as the weather permits. Fertilizer and other nutrients can be added at this time. The garden site should be cleared of all debris and growth. Composted materials can be worked into the soil to contribute to the health of the garden soil. The garden may also be divided into planting sections at this time.
Planting Cool Weather Plants
Peas and broccoli are two vegetables that can be sown directly into the garden as soon as the soil is workable. They thrive on the cold weather. As the weather gets a little warmer, plants like lettuce and cabbage should also be planted. Squash and cucumbers prefer the cooler temperatures as well. Hot weather will make lettuce "bolt," or go to seed, causing it to become bitter. A fall crop of cool weather plants may be grown for a late fall harvest.
Guarding Against Frost Damage
Plastic milk jugs and buckets can be used to guard against damage when an unexpected late frost occurs. You simply cut off the bottom of the milk jug and place it over the plants. Placing five-gallon buckets over larger plants works well to protect them from frost. Large areas can be covered with plastic drop cloths or other material. Remove the coverings when the air temperature starts to warm. Do not wait until the sun is high in the sky, or the plants can suffer from sun or heat damage.