Starting vegetable plants in a greenhouse is a great way to get the most out of the gardening season. You can determine a planting schedule based on the best times to place specific vegetables in your garden. Some seeds only take two weeks to germinate before transplanting, while others need up to twelve weeks. Your seed starting and transplanting schedule will also be informed by the cool-weather or warm-weather nature of the vegetables you might like to grow.
Plant frost-tolerant crops in your greenhouse first. Start these in December or January. Harden them off by gradually conditioning them to outdoor conditions over a few days. Transplant them in your garden beginning in February or March. Common frost-tolerant vegetables include beets, leafy salad greens, Swiss chard, spinach, bulb onions, turnips, radishes and carrots. Beets and carrots can be continually transplanted from March through August or September. Bulb onions can transplantes as early as January. These are the hardiest and most frost-tolerant of cool-season vegetables.
Start most cool weather vegetables in the greenhouse beginning in March. Recommended cool weather crops include broccoli, cabbage, cauliflower and lettuce.These prefer average ambient growing temperatures of 55 to 65 degrees Fahrenheit. Harden off and transplant these crops beginning in April. As a general rule, hardy and cool-season crops require a longer germination period than warm-season varieties, usually seven to twelve weeks.
Start warm-season vegetables in your greenhouse beginning in March and April. They are not frost tolerant and most germinate well in four to eight weeks. Gardeners in higher elevations, where freezing temperatures can occur well into spring, may prefer to wait until mid-April or early May. Where freezing temperatures are rare, wait to harden off and transplant warm-season crops until average temperatures reach the preferred minimum of 70 F. These include favorites like tomatoes, vining beans, cucumbers, legumes, squash, peppers, eggplant, potatoes, peas, corn and melons. You can also follow this planting schedule for starting warm-season ornamental annual flowers.
In temperate Mediterranean climate regions, you can start a second crop of cool-season vegetables in preparation for the cooler temperatures and rains of autumn. Start these in your greenhouse during July and August. Harden off and transplant them late in August and September. You can harvest these later in autumn through the next early spring.
Your Planting Articles
- Colorado State University Extension: Vegetable Planting Guide
- Oregon State University: Growing Warm-Season Vegetables in Cool-Season Areas
- University of California: Growing Vegetables from Seed
- Texas A&M University: Cold Tolerance in Vegetables
- The Weather Channel/Weather.com: Average Dates of Last Freeze (Map)
- University of Illinois Extension: Starting Vegetable Seeds Indoors
- University of Idaho: Short Season Vegetable Gardening
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