Getting down to brassica tax

A guide to indoor seed starting

By Soncirey Mitchell
Reader Staff

Don’t be fooled by the smattering of snow on March 24 — the first day of spring came and went, signaling the start of gardening season whether the weather cooperates or not. If you’re just getting into gardening and are looking to save some money growing starts from seed, here’s a guide to turning any space into a miniature nursery.

Clear plastic containers make perfect seedling terrariums. Photo by Soncirey Mitchell.

Know before you grow

Depending on specific geographical features, the U.S. Department of Agriculture designates Bonner County as “Zones 6b-6a” on the plant hardiness scale, meaning the average extreme minimum temperature falls between -23.3 and -15 degrees. By comparison, California’s San Joaquin Valley, dubbed the “breadbasket of the world” for its food production, is designated as “Zones 9b-10a.”

Given our cold climate and short growing season, which extends from the last frost in mid-May to the first frost in late-September, anyone looking to grow their own produce needs to buy or grow starts to get a proper harvest from most vegetables.

Cold-weather crops like brassicas (think broccoli, cauliflower and cabbage) and alliums (onion and leeks) can be sown as early as March 5, but gardeners should wait until April to plant summer crops like tomatoes and squash. Not everything can or should be started indoors; root vegetables, leafy greens and peas grow directly in the garden.

Becoming a closet gardener

There are eight key ingredients to growing and sustaining starts: seeds; seed starting mix; fertilizer; pots; containers; and an LED light, space heater and fan.

Seed packets from any local gardening store will do the job, but if you’re interested in high-quality, diverse produce suited for our climate, look at websites like Snake River Seed Cooperative, Adaptive Seeds or Deep Harvest Farm. A packet of 30 Snake River tomato seeds costs $4 and can last several seasons if stored properly. Seed packets labeled “heirloom” or “open pollinated” are best for would-be seed savers, as it’s more likely that the next generation of plants will be “true-to-type,” with the advantageous characteristics of their parents.

Seed packets in hand, find a closet or other small room to convert into a mini hothouse, making sure anything inside can withstand heat and humidity for at least three months.

Starts need lots of water, heat and light, but don’t waste money on expensive grow lights. When setting up my closet garden, I wandered the lighting aisle at Home Depot until I stumbled upon a three-foot LED shop light for approximately $18, which I plugged into a waterproof surge protector and hung from a wire shelving unit. Grow lights are only necessary if you intend to take your tomatoes from seed to fruit indoors, otherwise LED lights will satisfy the plants until it’s time to move them outside.

Finally, change into some classy Bermuda shorts, plug in the space heater and crank the temperature to 70.

A handy chart outlining planting timelines, with information courtesy of Idaho Master Gardeners.

Trashy tomatoes

To keep the nursery from becoming a desert, gardeners can give their starts consistent moisture by encasing them in pseudo-terrariums — and that requires a bit of dumpster diving. Clear plastic boxes from takeout, snack mixes or salad greens can be reused year after year to create a humid microclimate that keeps the seeds or seedlings from drying out overnight or during business hours.

Begin by washing the containers in hot water and diluted bleach to kill off any harmful diseases. Rinse well, then fill them up with nursery pots, cutting the tops off if necessary. If you’re having difficulty finding nursery pots in the right size, substitute by cutting large holes in the bottoms of plastic cups. Plants with sensitive roots (like leeks) should be sown in a biodegradable pot made from peat or cardboard to minimize the risk of injury when eventually transplanting them outside.

Fill the pots with seed starting mix — this is different from potting soil — and plant your seeds as specified on the packet. To water, fill the plastic container rather than displacing the seeds by drowning them from above. Bottom watering keeps the mix stable and ensures an even distribution of water.

Seal the seeds inside their recycled terrariums and tuck them away, checking the moisture level twice daily. When seedlings emerge, begin switching the LED lights on during daylight hours. Starts can stay under the plastic for as long as they’ll fit; but, after germination, gardeners should crack the lids or leave them open during the day to ensure proper airflow and keep the plants from rotting.

Seeds contain all the nutrients needed to sustain a plant until they outgrow their first leaves (or cotyledons), but once the second set of leaves sprout, it’s time to incorporate small amounts of fertilizer into their water. Always follow the instructions on the label to avoid burning the plants. At this stage the starts will need a gentle jiggle every so often — or better yet, a breeze from a nearby fan — to encourage them to strengthen their stems.

If you follow these instructions, your plants will spend their infancy under perfect conditions and therefore be totally unprepared for the cold, bitter reality of the outdoors. Shoving them in the dirt without acclimating them to the harsh sun or shifting temperature will kill them. Therefore, when they’ve outgrown their terrariums begin bringing them outside. 

Start with one hour in indirect sunlight, and add an hour every day for one to two weeks, increasing the intensity of the sunlight until they can survive a full day under the conditions in your garden.

Plant the starts outside and voilá — the real work begins.

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