It’s time to start planting the vegetable garden.
Some of the most popular vegetables can’t be grown from seed planted directly into the garden soil, because our growing season isn’t long enough. It won’t be safe to plant until after our last frost, and our frost-free date is around Memorial Day.
Pepper and onion seeds need to be started about eight to 12 weeks before they are transplanted, and eggplant and tomatoes need a six- to eight-week advance. Seeds for these will need to be sown indoors in mid- to late-March in order to have plants ready to go on May 30.
Cold-tolerant vegetables such as lettuce, cabbage and broccoli also benefit from an early start. Although they take only five to six weeks to reach transplant size, they are frost tolerant and can be set out in late April.
Browse a good seed catalog or the rack at your favorite store, and you’ll quickly realize that the selection of varieties is often better than you’ll find at the greenhouse in May. Check the days to maturity on the packs to make sure your plants will have time to produce and ripen in our 120 to 130-day average growing season.
Start with sterile planting trays. If you’re reusing old cell-packs and flats, be sure to rinse them well with a diluted bleach solution. I like to use the mini-greenhouse trays available almost anywhere gardening supplies are sold. These hold your flats in a watertight tray, and have a clear plastic dome to keep seedlings in a humid, draft-free environment. I’ve also repurposed clear plastic deli and salad containers with good results.
Use new soil, never re-used, and choose a product labeled as a seed starting mix; generally a very light, fine, peat-based mix with just a bit of perlite or vermiculite. Paired with sterile containers, you have the best defense against “damping off,” a fungus that causes seedlings to rot at the soil level and die.
Put the cell packs in the flat and fill loosely with soil mix. Make sure edges and corners are full, and level off the tops with a flat stick. Tamp the soil down gently using an empty cell pack of the same size.
For ease of care and identification, plant only one type of seed per pack. Place two or three seeds in each cell, at the depth recommended for the type. Cover with a dusting of potting mix, and gently tamp down again. Label each pack for the variety.
I like to use strips of old plastic mini-blinds or cut-off plastic knives. Keep them short enough to fit under your cover.
To water in and settle the soil, put a half inch of water in the watertight trays. Set your seeded flats inside and allow them to gradually absorb moisture from below, but once the soil is moistened, don’t let the packs sit constantly in standing water. Cover with the greenhouse dome and set in a windowsill or under a light.
We grow our seedlings under inexpensive shop light fixtures, hung from the ceiling in a spot rigged in the basement. Standard daylight bulbs have provided excellent results; costly plant lights won’t make a difference to these short-term indoor residents. Use a timer to turn the lights on and off automatically, set for 12 to 16 hours of light. A seedling heat-mat placed under the trays will enhance germination and growth — but don’t put this on the timer.
When the seedlings start to touch the cover, remove it. Begin fertilizing with a water-soluble product, mixed at half strength for indoor plants. A small oscillating fan set on low will help strengthen stems and keep plants healthy until it’s time to move them outdoors.