This time of year, I’m ready to garden. Yet even though air temperatures are already peaking into the low 70s, night temperatures are still cold, and soil temperatures remain well below 50 degrees. Planting seeds in such cold garden soils often results in greatly delayed or reduced germination — or even, at times, complete crop failure.
Although the seeds of many families of vegetables (carrot, beet, lettuce, onion, cabbage, etc.) can germinate at temperatures as low as 32 to 40 degrees, the ideal soil temperature for germination ranges from 70 to 85 degrees, depending on the crop. Even at those ideal temperatures, it can take anywhere from two to 12 days — and two to seven or more weeks at minimum soil temperatures — for these veggie seeds to pop! Worse yet, until a seed germinates, it’s particularly susceptible to rot in our cold, wet spring soils. Such realities can put a serious crimp in one’s instant-garden plans. There are tricks for warming the soil: laying a black material over it, or using clear-plastic cloches/mini-greenhouses. (Combining these two techniques works even better.) Using raised beds is another somewhat-effective option.
Still, these strategies aren’t as reliable as growing or buying transplants. As Elliot Coleman writes in The New Organic Grower, “A seed sown in the field is a gamble; a healthy 3- to 4-week-old transplant is an almost sure harvest.”
Over the years, I have transplanted just about everything — even carrots! We achieved that supreme level of gardener lunacy because in California, waves of slugs and snails mow down virtually all veggie seedlings in their infancy. So we designed deep flats with removable bottoms that enabled us to transplant blocks of carrots once they’d grown past the highly vulnerable infant stage.
Raising seedlings in the protected environment of our homes or beneath a simple plastic tunnel/cloche or cold frame lets us get a jump on the season. And if you’re ready for the challenge, you stand to gain much by growing your own starts. You can choose varieties that work for you. Perhaps even more importantly, you can gain more control over when you set out your plants. The lateness and poor selection of fall-transplant offerings at local retail outlets demonstrates the need for such control. Items like brussels sprouts, for example, should be set out by early July at the latest, yet they’re hard to find before late July at the earliest.
This is not an indictment of our nurseries, garden centers or farmers’ markets; they are merely responding to the buying public’s misconceptions. Just as our growers must sell flowering plants in bloom despite the fact that such specimens are inferior, they must also offer fall transplants when folks want them — not when they should be planted.
If you pot up your starts in a timely manner, keep them evenly moist, pay attention to their nutrition, and harden them off before setting them out, you can count on starts that will hit the ground running and never look back. You can further finesse your transplant production by gently brushing the tops of your plants several times a day. This mimics outdoor stresses, encouraging stocky starts.
You should also have a better shot at ending up with transplants that are disease- and pest-free. Be careful not to introduce infected plant material or contaminated pots and flats to your propagation operation. Such basic, common-sense precautions can go a long way toward ensuring healthy starts.
To help suppress disease, I rely on compost-based potting soil: 1 part well-made compost, 2 parts peat or coir (a coconut-fiber peat substitute), 1 part vermiculite and 1 part perlite. (Wear a mask when mixing this recipe!) I find that if the compost is high quality, I don’t need to add other amendments.
If you’re in doubt about your compost’s nutritional profile, you can amend this mix. Coleman’s recipe for amending potting soil calls for equal parts greensand, colloidal phosphate and blood meal. He recommends adding 3 cups of this “base fertilizer mix” and 1/2 cup lime to 80 quarts of potting-mix.
To boost your compost’s microbial vitality/ability to suppress disease, try Ruth Ostranga’s trick of spraying the surface of a newly seeded flat with fish emulsion. This encourages a benign fungal growth that inhibits damping off. Compost tea made with a commercial formula tested for disease suppression is another cost-effective way to augment less-than-perfect compost. You can find a list of sources for tested commercial compost-tea products at www. soilfoodweb.com.
Note: Savvy professionals take advantage of North Carolina’s bargain rate for waste analysis (a mere $4) to test their compost’s suitability for use as potting soil. Your local Agricultural Extension office has the forms and should be able to help you interpret the results.
Seed-starting infrastructure can be as elaborate or as basic as you choose. I recommend starting plants under shop lights equipped with both a cool and a warm bulb. There’s no need to invest in grow-light bulbs; these shop lights are cost-effective and conic — ready to plug in. Hang them from a ceiling or shelf using chain or rope, so you can move the lights up as the seedlings grow (this is critical, as the lights should be kept within a few inches of the seedlings). Two sets of shop lights with their reflectors should provide the proper width for a standard flat. A 4-foot set of lights will accommodate four flats; an 8-foot set of lights will cover eight flats.
To ensure that your plants don’t dry out while you’re at work, you can buy mats that wick water to seedlings. And if you want to grow the heat-loving plants, a thermostatically controlled heat mat is almost indispensable. High humidity enhances germination; either clear plastic bags or those nifty, clear-plastic domes designed to just fit over flats are a great way to achieve it. After germination, remember to remove the domes or bags to avoid humidity-induced fungal infections.
I generally use this light setup until the seedlings have about two sets of true leaves. At that point, I want them to be getting lots of real sunlight. This is where a simple PVC-and-plastic-sheeting mini-greenhouse/cloche will serve you well. (Beware the windowsill solution: If your plants start looking lanky, they probably aren’t getting enough light.) If you do go with the mini-greenhouse, pay attention to the high and low temperatures; you may want to just bring the seedlings inside on cold nights and days. For info on the required temperatures for various veggies, refer to Nancy Buber’s New Seed Starters HandBook.
If you don’t want to bring your babies in and out each day, reasonably priced soil-warming cables are another option. I also recommend using moveable insulation (such as heavyweight row cover) for the outside of the greenhouse/cloche at night and lightweight row cover for pulling over the starts inside the greenhouse. On sunny days, you’ll need to vent the greenhouse/cloche. Be careful when you vent, however, especially until the trees leaf out: Our spring breezes can dry out flats up to three times a day, so stay on top of your watering. If you can’t be there to keep up with all the watering, use the wicking mats. And if you count the work of caring for your starts for the pleasure it is and don’t factor in your labor, you will probably save some money, too.
If all this sounds like too much work or trouble, no problem — there are some fine transplants for sale out there. Just remember that you want vigorous, stocky plants that are stress-, disease- and pest-free. If you’re an organic grower, also be aware that conventional transplants may need some coddling as they adjust to the rigors of the organic-soil food web and wean themselves from their conventional fast-food diets. Later in the season, as the various farmers’ markets open, an abundance of organic seedlings should be available for sale.