Growing your own seedlings to transplant to your schoolyard garden is a great way to get your students thinking about their vegetable garden in winter, and can help you get a jump start on spring. By planting transplants instead of seeds in your garden, your vegetables will be ready to harvest sooner. Cool season vegetable seeds can be started in February, 4 to 7 weeks before transplanting them outdoors into your garden.
A few things to consider when choosing your vegetable seeds and starting them under lights:
- Time—The seedlings will need to be watered and checked on every day of the school week. Before starting seeds under lights, ensure that your classroom can commit time to this project.
- The last day of school—Make sure that you choose vegetables that will be ready to harvest before the end of the school year. Salad greens like lettuce and spinach are a great start.
- Spring Break—Most spring breaks fall in mid-March, so we recommend planting the garden after this week. Will someone be in town and at the school so that they can water the seeds during spring break?
- Having the right materials—Starting seeds in a windowsill does not usually produce healthy plants, since the light levels are too low, and plants become long and stringy when they stretch towards the sunlight. The best method for starting seeds indoors is to grow them with the help of fluorescent lights.
Materials you will need:
- Grow light unit (You can buy one, or make your own using wood, PVC pipes, shelving, etc.)
- Light timer
- Cell packs, peat pellets or other growing containers
- Pro-mix or other soil-less growing mix
- Vegetable seeds from KCCG
- Plastic bags or plastic flat covers
- Spray bottle with mist setting
- Watering can with fine spray
- Short plant marking stakes and felt-tip marker to label cell packs
Start seeds indoors under lights approximately 5 to 9 weeks before you want to transplant the seedlings to your schoolyard garden. The florescent lights will produce enough light for the plants to grow, so you do not need to place your grow light unit by the window. In fact, you want to make sure that the grow light unit is situated away from any drafty windows or heating vents/radiators as extreme fluctuation in temperatures may adversely affect plant growth.
Plants grow best directly under the lights. The number of seedlings you can grow in your light unit depends on how many lights you have. Typically, you can only fit one row of cell packs under a fixture with two florescent light bulbs. If you want to grow a row of standard flats, you will need a bank of 3-4 light fixtures.
- Put your pro-mix in a large container or tub and mix with water until pro-mix is moist.
- Loosely fill your cell packs with moistened pro-mix, leaving ½ inch space at the top of each cell.
- Set 2-3 seeds on top of the pro-mix near the center of each cell.
- Sprinkle dry pro-mix on top of seeds so that the seeds are lightly covered.
- Using a spray bottle, mist the 6-packs until top ½ inch is moistened (soil will turn darker).
- Cover cell packs with plastic bag or covers.
You are now waiting for your seeds to germinate. Place plastic covered cell packs in the grow light unit. Adjust the lights so that they are 2-3 inches above the top of the cell packs and turn on the lights. If the soil has dried out, remove the plastic from the cell pack, mist with water and then replace the plastic covering. Check the cell packs every day to see if your seeds have sprouted. Once you see the first green shoot emerging from the soil, remove the plastic covers and place the cell packs under the lights.
Although the light given off in the grow light unit may seem bright to you, it is still much weaker than the light given off by the sun. When seedlings do not get enough light, they stretch towards the light and become long and thin. These are not healthy plants.
- In order to prevent stretching, the lights need to be kept at 1 inch (or less) above the tops of the plants at all times. Check the grow light unit each day and make adjustments as needed.
- The center of your florescent lights is much more intense than the 12 inches on each end. Rotate your plants to keep them growing evenly.
- It is recommended that you allow your plants 16 hours with the lights on, and 8 hours with the lights off. You can use a simple light timer to turn on and off the lights so that lighting is consistent, or you can simply turn the lights on when you are at the school, and off when you leave for the day.
If more than one seed sprouts in a cell, remove the extra seedlings. If possible, leave the strongest looking plant that is growing closest to the center of the cell. Thin plants before they reach 1 inch in height. Try not to disturb the plant that you want to keep. Use tweezers to remove the extra seedlings. For best results, thin when the soil is moist.
Use room-temperature water to water your plants. Once the plastic wrap is removed from your plants and they are under the lights, they will dry out faster and will need to be watered more often.
Misting with the spray bottle will not moisten the soil enough for young seedlings. Once plants are established (3-4 inches tall) you may water from the top with a watering can. Young seedlings are fragile and a heavy watering can knock them down. It is best to water them with a fine spray.
Plants need nutrients to grow: too much and they will be too tall, too little and they will be stunted. Start fertilizing as soon as plants sprout. Use liquid fertilizer at half-strength. Fertilize once a week.
Transitioning to the Outdoor Garden
Planting your plants directly from your grow lab into your garden can shock your plant and keep it from growing to its full potential, because light levels outside are 10 to 20 times stronger than the light level in your grow light unit, which can cause the plants to sunburn when they are planted outside.
Cold temperatures and strong wind can shock the plants. A week before you want to transplant the seedlings to your outdoor garden, “harden off,” or acclimate the plants by moving them outside for short periods of time during the day, increasing the amount of time in the sun each day.