When to Start Growing Greenhouse Vegetables

Cool-Season Vegetables

• Cool-season vegetables like lettuce, spinach, kale, Brussels sprouts, cabbage and broccoli often are planted directly in the ground once the final frost has passed. The reason for this is these plants' ability to thrive in cool climates. Conversely, when temperatures reach the high 70s and 80-degree mark, leafy, cool-weather vegetables fail to thrive. To get an even earlier start on your cool-season vegetables, start seeds in peat pots 10 weeks prior to the final frost date. Transplant your starts from the greenhouse into the garden after the final frost date. Be aware that leafy vegetables do not transplant well, so use porous, biodegradable containers that can be planted directly into the ground. Ensure that the entire peat pot is below the surface to prevent moisture loss.

Warm-Season Vegetables

• Warm-season vegetables like cucumbers, watermelons and squash that are intended for future outdoor growth should be started in a greenhouse four weeks prior to outdoor planting. Plants like tomato, eggplant and pepper require longer growing seasons and yield multiple harvests. They should be started indoors seven weeks prior to your area's last frost date. Local meterologists and farmer's almanacs often provide geographically specific final frost dates. Vegetable seed packets provide information on the number of days until the seeds mature. Subtract the number of days until maturity from your area's last frost date to determine the best time to start seeds inside your greenhouse.

Growing Seasons

• Your area's growing season is the time period between its last and first frost date. Some growing seasons are very short, making it necessary for gardeners to start their plants indoors, or to keep them indoors for their entire growth cycle. Warm-season vegetables are started and grown within heated greenhouses during any season or time of year. Be aware that not all crops can be grown simultaneously within a greenhouse because they require different temperatures. If you plan to grow a variety of crops, start with cool--season vegetables during cool, outdoor weather. Harvest these vegetables then plant your warm-weather crops. Greenhouses equipped with adequate lighting, heat and water resources can produce crops year-round.

Considerations

• Greenhouse growers experience different growing dilemmas than other gardeners. Space, both overhead and at ground level, is limited. Diseases spread quickly without proper spacing and aeration. Choose vegetables that grow vertically, such as vining tomato varieties, to use space efficiently. Plant disease-resistant seeds and ensure that spacing recommendations are properly maintained.