Once you have decided on your greenhouse plans you will need to know how to take care of your seedlings properly inside your greenhouse. Whether you are using a window inside your home or you have an outside structural greenhouse there are some beginner greenhouse gardening tips that will make things easier for you while yielding the best results.
When to Start your Seedlings
Historically Memorial Day represents the opening of gardening season. It is typically when the weather has settled from winter and you can anticipate warmer temperatures at night. In order to plant at the end of May you will need to start your seeds early enough that the plants are strong enough to withstand your outside garden.
You will plant your seeds 6 to 8 weeks before the average date of last frost for your area. To find this information you can check with the Old Farmer’s Almanac. Today there are many websites that can tell you, including Modern Farmer’s own quick and handy frost chart. Find your areas average date and subtract six to eight weeks and plant your vegetable seeds indoors.
Greenhouse Gardening Tips
You may choose to plant your seeds in a single large container or you can use individual cell trays or small pots. You will need enough small pots or cell trays to hold all your desired plants. You will also need a good quality seedling mix.
A good quality organic mix designed for seedlings will be fast draining, and light. It will usually contain sphagnum moss and perlite or vermiculite. These mixes are formulated to encourage strong, healthy growth in new plants.
Regardless of how perfect seeds may appear, germination is never guaranteed. Because of this, multiple seeds are always planted, usually two seeds in each cell of a seed starting tray. This provides a better chance at least one in each cell will take root.
When the seedlings are at least a couple inches tall, and have reached their “true leaf” stage, which is when each seedling has sprouted a second set of leaves, it’s time for a process called selective thinning.
Thinning Out Your Crops
Selective thinning prevents overcrowding, so seedlings don’t have any competition for soil nutrients or room to grow. This process should be done several hours after watering to minimize stress on the remaining sprouts.
When thinning, carefully inspect the seedlings in each seed starting tray cell and determine the stronger of the two. Look for fleshy leaves, upright stems, and center positioning in the space.
Using a small pair of scissors, clip the smaller, weaker, more spindly looking seedling. This is also the seedling that is less likely to survive. Cut the undesired seedling as close to the soil line as possible, so nutrients go directly to the remaining plant. Another option is to pull the seedling out completely, but this could cause root disturbance to the remaining sprout.
Once selective thinning is complete, there should only be one seedling in each cell of the seed starting tray. Not only does this allow for better growth, but it also creates better air circulation for all the neighboring seedlings as well.
If both seedlings look strong and healthy you can transfer one seedling out into its own tray or pot.
Tranferring Seedlings to Individual Pots or Trays
As seedlings outgrow seed starting cell trays, they need to be transferred to individual pots, or larger trays. This process should not be done until the seedling has hit its “true leaf” stage. The first set of leaves are the cotyledons, or seed leaves. The second set are the true leaves, which better resemble the leaves of the mature plant.
Fill the new, larger pot with good quality seed mix, and poke a hole in the center of the container or larger cell. Place the seedling in the hole and gently firm up the surrounding soil.
Always avoid handling the seedling by its tender stems, which bruise easily – always use their seed leaves.
Notice the strong root system and the green, fleshy leaves. Transplanting is best in the late afternoon or evening, so seedlings lose the least amount of water and can recover from the move overnight, when temperatures are cooler. The growing seedling will remain in the new pot until it is ready to plant into the ground. Seedling Maintenance in the Greenhouse – The Martha Stewart Blog
“Hardening Off” Getting Your Plants Ready for the Outdoors
About 10 days to two weeks before the time to move the plants outdoors you will need to begin to prepare your plants for survival outdoors. Plants cannot go outside without a period of “hardening off.” This means gradually introducing them to the outdoors to avoid the shock of temperature changes, sun and wind.
Some advise bringing the plants in at night and putting back out the next day.
- Begin 7 – 10 days before your transplant date.
- Place plants in a sheltered, shady spot outdoors. Under a tree or even on your back porch is fine. Leave them for 3-4 hours and gradually increase the time spent outside by 1-2 hours per day.
- Bring plants back indoors each night.
- After 2-3 days, move the plants from their shady spot into morning sun, return them to the shade in the afternoon.
- After 7 days, the plants should be able to handle sun all day and stay out at night, if temperatures stay around 50 degrees F. Keep an eye out that the soil doesn’t dry and bake the plants, if the weather is warm.
- After 7 -10 days your plants are ready to transplant. Try to do so on a cloudy day and be sure to water well after planting.
Congratulations you have now started your own seeds, thinned out your seedlings so that you have a nice hardy plant, and planted your crops outdoors. Now all that is left is waiting for the them to mature! You will soon be enjoying fresh fruits and vegetables that you grew yourself.