Growing plants in a garden can be difficult if your region experiences frequent changes in temperature, moisture, and weather. Changing conditions can make it especially hard to get started growing plants from seeds. A simple solution is to grow plants, flowers, and vegetables in a greenhouse, where you can control all of the climate conditions to provide plants with the optimal temperature and moisture they need to thrive. Once they have hardened off and acclimated, you can transfer the plants to your garden.
You can sow seeds in your greenhouse in any season. Plant seeds in your greenhouse about six to eight weeks before your last frost so they will be ready to be transplanted in the spring.
If you are planting large seeds, such as beans or tree seeds, soak them in a bowl of warm water overnight before you plant them. Put moist potting soil in seed-starting trays with one seed per tray. If you are planting very small seeds, spread a few across the surface of the soil and press them down.
You can sprinkle a very thin layer of vermiculite or sphagnum moss on top of the soil, unless the seeds need light to germinate. Petunias, lettuce, and small herbs require light to grow. Spray a fine mist of water over the surface of the soil. Water the seeds as necessary to keep the soil moist. If the seeds need constant moisture or high humidity, put the seed trays in a clear plastic bag until the seeds germinate.
Maintain a temperature in the greenhouse of about 70 degrees during the day and 50 degrees at night. If you need to run a heater, open a door or window for ventilation. If the greenhouse gets less than 16 hours of sun every day, put hanging fluorescent lights about six inches above the seed trays.
You can put the seed trays on a heating mat to make the seeds germinate faster. Try to keep the soil between 70 and 85 degrees Fahrenheit. A mat with a thermostat can keep the soil from getting too hot.
When the first true leaves appear, apply an all-purpose, soluble fertilizer at half strength. Thin the seedlings so there is one healthy plant in each tray cell and transplant them to larger containers when they have two or more true leaves. Leave enough space between the containers to allow for proper air flow. Keep a fan on at all times to provide a gentle breeze and help the stems grow strong and thick.
Start to harden off the plants two weeks before you transplant them to your garden. Do this in early spring or after your last frost. Put the plants in a shady outdoor area for a few hours every day, gradually increasing the length of time they are outdoors. When the hardening off is complete, you can move the plants to your garden.