Many plants you want to grow outdoors can be started inside your greenhouse in late winter and early spring, two to three months before your frost-free date. This can give you a full-looking flower bed or vegetable garden as soon as temperatures are right for your types of plants. To do this, you'll need to know how to plant seeds in a greenhouse for the best results and good germination. While the process of planting seeds in a greenhouse isn't much different from doing it outdoors, the greenhouse can give you a jump start on your garden.
Fill your seed pots with soil or starter mix and place inside the seed tray. If using Jiffy pots, place the disks in the tray.
Set the tray in an area of the greenhouse which receives at least six hours of sunlight a day and is easy to get to for daily observation and care.
Add water and let the pots absorb it until they are completely moist. The Jiffy pots should have expanded fully to almost 2 inches tall. If there is excess water in the tray, make sure to pour it out so the plants aren't over watered.
Plant your seeds into the pots at the depth and quantity specified on the packaging. Only cover the seedlings if required. Often, vegetable seeds will need covering while flower seeds do not, so be sure to look at the individual labels for each type of seed you are planting.
Cover the seed tray with a clear or frosted plastic lid, or plastic wrap, to seal in the moisture. Even though you are inside your greenhouse, which tends to have moister air, you'll still want to maintain as much moisture as possible in the soil around your seeds.
Water as needed to keep your soil evenly moist during the first six to eight weeks. As the seedlings become tall enough to reach the lid, remove it and allow the seedlings to grow unrestricted.
Plant your seedlings outdoors in prepared soil, or move them to a larger container, after two to three months. Transplanted seedlings will need watering for the first month as the roots grow; when new growth appears you'll know the roots have become established.