Our office seed starting project has been a glowing success so far. Just three days after we planted our seeds, a few tomato sprouts had already broken ground! A few days after that, the peppers did the same. And both have been growing like crazy ever since — especially the tomatoes. Our excitement has been accompanied by a lot of learning, and I’d like to share some seed starting tips based on our experience. (Check out our What to Plant Now tool to learn which seeds you can start indoors in your area right now — there's still time!)
Seed Starting Supplies
Seed starting trays. You can pick up various sizes of seed starting trays at your local garden center. These usually come with one tray with dividers and holes in the bottom, and one flat tray without holes to set the first tray into. If you don’t want to purchase a setup like this, you can use recycled materials. For example, clean, empty yogurt cups with holes drilled in the bottom could be set inside a large baking pan to create a great tray kit. Making your trays is a perfect opportunity to get creative.
Seed starting mix. For best results, start seeds in an organic seed starting mix. These mixes are very fine and will hold water well. A small bag will cost about $5 at your local garden center.
Seeds. Consider planting heirloom varieties (see our article, Heirloom Vegetables: 6 Advantages Compared to Hybrids). Also, only use seeds from previous seasons if they’ve been stored properly in a cool, dry place.
Timer for your grow light. A timer isn’t a necessity, but it sure is handy. We plugged our grow light into an automatic timer, setting it to give the plants 18 hours of light per day.
Planting. For tomatoes and peppers, we planted two seeds per compartment with the intent to thin them later. We then covered the seeds with about a quarter inch of seed starting mix and gently patted down the soil.
Watering. For the most part, you’ll water your seeds via the bottom tray. When you first plant the seeds, however, you can give them a few good waterings from the top (but use a watering can with a gentle spout). Water lightly once, wait about an hour, water lightly again and so on until the seed mix is nice and moist. Also, fill the bottom tray up with about three-quarters of an inch of water (adjust based on the tray materials you’re using; you want to make sure the holes in the bottom of your primary seed trays or cups are surrounded by water).
Grow light. It’s not necessary to put your plants under a grow light until they actually sprout. When they do, place them as close to the grow light as you can (we set books under our trays to get them to the desired height). Then simply move the trays down as the plants grow.
While Your Seeds Grow
Watering. Keep an eye on the water in your bottom trays. Add water every few days or so, as required. There's no need to water the plants from the top at this point.
Temperature. The temperature of the room where your seeds are growing will affect their growth rate. Our tomato sprouts grew extremely rapidly, and we think it’s because they were at a pretty consistent temperature of about 68 degrees Fahrenheit both day and night. It’s best for your seeds to be growing in the 50 to 60 degree range. Ours grew so quickly that they look a bit tall and spindly (though still healthy), and a cooler temperature could have slowed them down a little and resulted in sturdier stems.
We grew our seeds in a grow light bookcase (see Multipurpose Plant Grow Light Seed Starting Bookcase for plans on how to make your own), and we noticed that the seeds growing on the middle shelf seemed to be getting a bit of extra warmth from the light mounted directly underneath it. This is something to consider if you have a similar setup. We’ve tried to solve this temperature issue by placing a sheet of insulation board underneath the trays on the middle shelf (see photo).
Thinning. After two and a half weeks of growth, it was time to thin our tomato plants. Do this by cutting all but the strongest plant in each compartment. Cut the weaker plants at soil-level. This method won’t disturb the root system, as pulling the plants would do.
Petting. Yes, petting. This may sound strange, but if you gently wave your hand over the tops of the plants a couple times a day, it encourages them to grow nice and strong. (This step has been my favorite because it stirs up a lovely tomato smell.) The same thing can be achieved by pointing a fan at the plants to simulate mild wind.
Outdoor time. After a few weeks of growth, you can start setting your plants outside in the shade for about an hour per day. Just make sure you don’t expose them to rain, direct sun or heavy winds at this point. Setting them out will help your plants “harden off” — prepare them for their upcoming lives in your garden.
Seed starting is not only fun, it can also save you money. We spent a minimal amount on seeds and materials, and we're growing 64 tomato plants and 32 pepper plants! Plus, you can experiment with varieties more freely when you're not limited to the starts available at a garden center.
Do you have any seed starting tips to add to this list? If so, please share them with our readers in the comments section below. Happy growing!
Shelley Stonebrook is MOTHER EARTH NEWS magazine’s main gardening editor. She’s passionate about growing healthy, sustainable food and taking care of our environment.
Photos by Sean Rosner and Megan Phelps.