Warm-season plants with a long growing season are especially vulnerable to frost damage early or late in the year. In cold northern climates with a limited growing season, starting gourds (Cucurbita spp., Lagenaria spp. and Luffa spp.) indoors before the outdoor growing season begins allows varieties with a long maturation period to thrive after they are transplanted to the garden. Many plant species are known as gourds, including plants in different genera, but all gourds share specific requirements that determine when their seeds should be planted.
Gourds are warm-season crops that need a long growing season free from frost. The best time to plant gourd seeds outdoors is in spring after the average last frost date. The National Oceanic and Atmospheric Administration maintains probability data for the first and last frost and freeze of the season in every state. Check NOAA's website for the data about your location. Gourd seeds planted in cold, wet soil often rot before they have a chance to germinate. Low lying areas with poor drainage and heavy shade often experience frost later or earlier in the season than the surrounding area. Planting gourds on relatively flat ground with full exposure to sunlight promotes healthy growth and reduces the risk of frost damage.
Seeds from gourd species in the Luffa genus need special preparation before they are ready to plant. Luffa seeds have a tough outer shell that inhibits germination. Rubbing the seeds between two sheets of medium-grit sandpaper helps break the coating on this shell. Soaking the seeds in room-temperature water for 24 hours completes the preparation process.
Gourds grow best when the average of the day and nighttime temperatures remains 70 to 85 degrees Fahrenheit. The plants typically need 100 to 180 frost-free days, depending on their species, to reach maturity and produce fruits. Gourds are ready to harvest when their stems dry out and turn brown. The best time to harvest gourd fruits is before the first frost in fall, but mature fruits with a hardened outer shell can tolerate a light frost.
Starting gourd seeds in pots indoors before the growing season reduces the risk of frost damage and lengthens the growing season in cold climates. The best time to start gourd seeds indoors is about four weeks before the average last frost of the spring season. Gourds are sensitive to having their root systems disturbed and grow best when they are planted in individual pots. Gourd seedlings are ready to transplant outdoors when they have developed four small leaves.