For people in northern climates, a greenhouse is a valuable structure to have in the spring months. It allows you to start seeds much sooner than you normally would be able to plant them in the ground. Using the sun's solar energy, greenhouses can be more than 30 degrees warmer inside than the outside temperature. Grow vegetables in a solar greenhouse to enjoy earlier harvests, and plant vegetables that would take longer to mature than your average growing season.
Fill plastic jugs or barrels with water to add thermal mass to your greenhouse. Use 2 1/2 gallons of water per square foot of wall and roof space. Place the full jugs or barrels wherever you have free space in the greenhouse.
Place two concrete blocks in your greenhouse and place a 2-by-12 board on top of the blocks to create a bench for your garden flats.
Set your garden flats on your benches and add soil to each one. Mix 1/3 garden soil, 1/3 compost and 1/3 sand to make a growing medium.
Plant seeds as directed on your seed packaging. Label each flat to correspond with the kind of plant that is in it.
Water the flats so that the soil remains moist, but not soggy. The individual amount of water needed will depend on the amount of sunlight, wind movement and soil mixture of your flats. Adjust watering accordingly.
Fertilize seedlings as soon as they emerge with a 20-20-20 soluble greenhouse fertilizer. Apply two to three times per week with the amount recommended by the packaging.
Transplant your vegetables to your garden once the threat of frost has passed in your area.