Seed sowing & propagation

A packet of seeds is one of the best bargains in gardening — a few pounds can fill a whole bed. But germination is also where most beginners lose plants, usually to a handful of avoidable mistakes. Get the method, depth, and conditions right, and raising your own plants becomes the cheapest and most satisfying part of growing.

Direct or under cover?

The first decision is where to sow.

• Direct sowing puts seed straight into its final position in the ground. It is simple and avoids transplant shock, which is why root crops like carrots and parsnips — whose taproots resent disturbance — are nearly always sown this way, along with fast crops like radish and large-seeded beans and peas.
• Module or tray sowing raises seedlings in cells or pots to transplant later. It gives a head start while the ground is still cold or occupied, protects vulnerable seedlings from slugs and weather, and lets you place each plant exactly. The cost is an extra step and the care that comes with it.

The depth rule and what germination needs

A reliable rule of thumb: sow a seed about two to three times its own diameter deep. Tiny seeds need only the lightest covering, or none at all; large beans go deeper. Sowing too deep is a classic cause of failure — a small seedling can run out of stored energy before it ever reaches the light.

Most seeds germinate when given three things: moisture, warmth, and air in the soil. Note what is missing — light. Many seeds sprout perfectly well in the dark; light only becomes essential the moment the seedling breaks the surface.

• Moisture must be steady: damp, never dried out and never waterlogged. This is usually the make-or-break variable.
• Warmth matters because each crop has a temperature range for sprouting. Tender, warm-season crops like tomatoes and peppers germinate poorly in cold soil, so gentle bottom heat from a propagator or warm windowsill lifts both speed and success.
• A few seeds actually need light to germinate and should be surface-sown rather than buried — always worth checking the packet.

From germination to sturdy seedling

Once seedlings emerge, the priority flips to light. Too little of it — especially combined with too much warmth — makes seedlings “leggy”: pale and stretched as they reach for brightness. Give them strong light immediately and keep them from getting too warm or crowded, and they stay short and tough.

When seedlings are crowded in a seed tray, they need pricking out — moving each one into its own pot or module so it has room.

Always lift a seedling by a leaf, never the stem. A crushed stem cannot recover, but the plant can replace a damaged leaf.

The cue for pricking out is the arrival of the true leaves. The very first leaves, the seed leaves (cotyledons), are part of the seed and often a plain rounded shape. The true leaves that follow look like the plant’s adult foliage and signal the seedling is robust enough to handle.

Watch, too, for damping off — a fungal collapse that topples seedlings at soil level, often overnight. It thrives on overwatering, stale air, and dirty containers, so clean trays, good ventilation, careful watering, and thin sowing are the defence.

Thinning and hardening off

Direct sowings frequently come up too thickly. Thinning removes the surplus so the keepers have space, light, and nutrients to size up. Thin in stages toward the recommended spacing, ideally on a still day so the scent of disturbed foliage does not draw in pests like carrot fly.

The final step before plants raised under cover go out is hardening off. Soft indoor growth would be shocked, even killed, by a sudden move into wind, sun, and cold. So over one to two weeks you expose plants to the outdoors for steadily longer periods, letting them toughen up gradually. Skip this, and weeks of careful raising can be undone in a single chilly night.

Master these few habits — sensible depth, steady moisture, bright light, gentle handling, and a patient hardening off — and the humble seed packet will repay you many times over.