The seed-starting season is upon us. Soon loads of colorful and alluring seed catalogs will be populating websites and mailboxes nationwide. For the ardent gardener, raising plants from seed has huge benefits. One can grow cooler homegrown plants from seed for less than purchasing from most garden centers, but it’s not without challenges. Even advanced gardeners find it tough to produce homegrown seedlings that are as robust as nursery-grown; the key is maintaining the right balance of light, temperature, soil, nutrition and water through good care and smart decision-making.
There’s a reason why seed-starting is popular. Gardeners can grow cooler plants, for less than the cost of purchasing from most garden centers.
Seedling woes and mishaps are many. Truth-be-told, the average seed grower tends to grow leggy, pale green, weak plantlets rather than stout, multi-stemmed, medium green ones. The causes are basic: poor light causes legginess and pale color and inadequate nutrition, poor soil and/or improper watering can all cause poor growth and weakness. This matters because weak seedlings have a higher mortality rate and are slower to establish, while robust seedlings look better, fill out faster, and yield more flowers and fruits sooner.
Good growing light is most essential because too little causes etiolation (long, spindly, pale growth) and too much causes foliar burn. Gardeners lacking a sunny conservatory or greenhouse should choose the next best thing, a light table. And for high-grade seedlings refrain from window-growing; even south-facing-window-light is rarely uniform or strong enough for robust growth. A growing table fitted with broad spectrum shop lights will do a much better job. Here are four growing table “dos” to abide by:
1. Do choose the right location and table. A warm, sunny room is ideal. Prefabricated grow tables (sold by many seed vendors) are handy but expensive. Standard 4-level utility shelves (sold at home improvement centers) fitted with shop lights are just as effective and much cheaper.
2. Do choose the right fixture and bulbs. Standard 48-inch shop lights can accommodate two flats of seedlings, and high-Intensity fluorescent bulbs have the broadest spectrum for good growth. (Avoid metal-halide high-intensity discharge (HID) bulbs, which are expensive, hot, and unnecessary.)
For best growth place seedlings 2 to 3 inches from high-Intensity fluorescent bulbs.
3. Do place your seeds and seedlings the right distance from the light. Pots and seedlings should be kept 2-to-3-inches from fluorescent bulbs and fixtures hung from chains for easy height adjustment.
Exposure to dappled sunlight can help seedlings adjust to natural sunlight more quickly.
4. Do slowly acclimate sun-loving seedlings to natural light before outdoor planting. Sunlight is stronger than artificial light and can burn tender seedlings. Over seven to ten days, slowly move seedlings from indirect outdoor light to full exposure—increasing exposure by two hours every two days.
Containers and growing medium are the next essentials. Standard six-cell, six-pack growing flats with non-draining trays are perfect for most seedlings, and Black Gold Seedling Mix, with its blend of high-grade Canadian Sphagnum peat moss and perlite, is recommended. Our seedling mix is also easily wetted and uniformly fine for light seed coverage. Light coverage is essential because most seeds naturally germinate on or close to the soil’s surface, so when planting seeds stick to the mantra “lighter coverage for lighter seeds and greater coverage for greater seeds.” Dust-like seeds can simply be sprinkled on the top of the medium, and large seeds rarely need to be planted deeper than ¼ of an inch—despite what some seed-starting guides advise. Seeds can also be lightly covered with Black Gold Washed Sand or fine Vermiculite instead of mix. Coverage with both is shown to reduce instances of “damping off” (seedling fungal disease); planting in fresh, unused mix also reduces damping off.
Small seeds are best surface-sown for successful germination.
Temperature needs vary from seed to seed and plant to plant; some like it cool and others like it warm, but most thrive at room temperature (68 degrees Fahrenheit). Warm-season plants, like tomatoes, peppers and zinnias, germinate and grow faster with warmer temperatures; a seedling heat mat will hasten germination and growth for these and other summer growers. A flat-sized heat mat costs around $25.00 and will last for years.
Good watering technique will make or break growing success. The key is remembering that overwatering is worse than underwatering . Too much water encourages fungal disease and root and stem rot, and invites pests like fungus gnats, whose larvae feed on seedlings, and shore flies, whose excrement damages seedlings. Once these problems are established, they are hard to get rid of.
Left: A plastic bottle with holes punched in the top makes a perfect seed waterer! Right: Be sure to allow only one seedling per planting cell for best success.
To avoid overwatering seeds and seedlings: (1) water gently and (2) water until mix is moist but not wet. These steps are most important before and right after seeds germinate because seeds and seedlings use less water and are easily drowned. A plastic water bottle with five holes poked into top makes a great gentle seed and seedling waterer (see photo). Bottom watering with a self-watering capillary mat is also recommended. Just be sure that no standing water remains at the tray base at any time.
Properly grown seedlings should have healthy roots to the bottom of the pot.
Once plants develop multiple leaves, more water can be applied. The amount ultimately depends on how quickly plants are growing and using water. It’s wise to check fast-growing seedlings twice daily to assess their water needs. If you think you may be watering too much, err on the side of less water. Slight wilting is better than rot and ruin.
Nutrition is not a factor until plants develop their “true leaves” (sometimes called the second set of leaves). In fact, fertilizer can actually inhibit seed germination and burn new seedlings, which is why good seed-starting mixes are always fertilizer free. Once seedlings have reached two inches or so, a feather-light sprinkle of Black Gold Starter & Transplant Fertilizer will keep them pot-healthy until planting day.
When the threat of frost has passed, incrementally introduce your flats of plantlets to the great outdoors. Incremental exposure allows tender plants to healthfully acclimate to the high light, wind and temperature changes of the garden. Start by placing them in a protected location with diffuse light and slowly move them into a more open spot with higher light. After seven to ten days your plants should be garden-ready, and if you follow this guide they should look like those grown by the pros!
Happy seedlings have good colors and are not leggy.
Homegrown plantlets, like these fennel, should only be planted in the garden after they have hardened off.
These newly planted homegrown cabbage seedlings are healthy and robust!
Those new to indoor seed growing should start with annuals such zinnias, cosmos, basil and gloriosa daisies.