Seed Starting for a First Food Garden

Starting your own seeds is the cheapest thing in gardening and the easiest to do badly. A packet of seeds costs about what one transplant does, and it contains dozens. The catch is that a seedling has requirements a mature plant does not, and getting them wrong produces pale, stretched plants that never really recover.

There are only four variables that matter: the medium, the container, light, and temperature. Get all four right and germination is close to boringly reliable. Get light wrong -- which is the usual one -- and nothing else saves you.

A seedling grows toward light. On a windowsill in late winter, the light arrives from one side and there is not much of it, so the stem stretches, the plant goes pale and floppy, and it falls over. Gardeners call it leggy, and it is not a watering problem or a soil problem -- it is a light problem.

The fix is a light source 2 to 4 inches above the leaves, running 14 to 16 hours a day. Modern LED strips run cool enough to sit that close, use very little electricity, and link together so one outlet feeds a whole shelf. It is the single highest-value purchase in this category -- see grow lights for seedlings.

Seed starting mix is deliberately fine, light and low in nutrients. Fine texture puts the medium in contact with the whole seed, which is what triggers reliable germination. Low nutrition is correct because a seed carries its own food supply until its first true leaves -- and a rich mix at that stage produces soft growth and fungal trouble instead of roots.

Once true leaves appear, that changes. The seedling has used its reserves and needs either a weak liquid feed or potting on into a richer mix. Skipping that handover is the second most common reason a promising tray stalls. Our picks are in the best seed starting mix, and the DIY recipe if you would rather mix your own.

Seeds respond to the temperature of the medium, not the room. Peppers and eggplants want soil in the 80s Fahrenheit to germinate briskly; a 68-degree house gives them soil in the low 60s, which is why they appear to do nothing for weeks. A heat mat under the tray fixes that.

Take the tray off the heat once the seedlings are up. Bottom heat after germination encourages soft, stretched growth and dries the tray faster than you will remember to water it. Cool-season crops -- lettuce, brassicas, peas -- do not want it at all, and lettuce germination is actively inhibited by warm soil.

Sowing too early is the classic first-year mistake. Seedlings started eight weeks before they can go outside become root-bound, stressed and leggy while they wait, and a stressed transplant is set back more than a later-sown one that went out at the right size. Work backwards from your last frost date -- when to start seeds indoors has the counts by crop.

And do not skip hardening off. A plant raised indoors has no defense against wind or direct sun; it needs a week of gradually increasing outdoor exposure before it is planted out. A cold frame makes that easy, which is part of why the greenhouse step comes where it does.

The failure that catches people out is damping off: a fungal collapse that fells a whole tray of healthy-looking seedlings at soil level, usually overnight. It is not a disease you treat once it has started -- the tray is gone -- so the entire strategy is prevention.

• Take the humidity dome off the moment most seeds have germinated. Still, damp air is exactly what the fungus needs.
• Give the seedlings air movement. A small fan on the lowest setting, a few feet away, is enough.
• Use a clean bagged seed mix rather than garden compost, which carries fungal spores and weed seed.
• Wash trays and pots between seasons. Reused dirty trays are the most common way the problem carries over from one year to the next.
• Water from below where you can, so the surface of the medium and the stems stay drier.

A packet of seeds costs roughly what one transplant does and contains dozens. For a bed that takes four tomato plants the saving is modest; across a full planting of brassicas, salad, beans and squash it is substantial, and it compounds every year you keep the equipment.

The bigger return is variety. Garden centers stock the handful of cultivars that ship and display well. Seed catalogs carry hundreds, including the ones bred for flavor rather than for shelf life, and for regional climates that a national retailer will not stock. That is the real argument for starting your own, and it is why this step sits ahead of composting rather than after it.