Seed raising is the cheapest way to fill a garden, and the most common failure is the same every time: tall, pale seedlings that flop over the moment they go outside. Stretching is not a disease, it is a plant reaching for light.

Light, much more of it

A windowsill gives light from one side only for a few hours a day. Seedlings need bright light from above for twelve to sixteen hours. A cheap shop light hung five to ten centimetres above the tray, raised as they grow, is the single biggest fix. Turn trays daily if a window is all you have.

Cooler after germination

Warmth speeds germination, but once the first leaves are up, move trays somewhere cooler. Warm and dim is the exact recipe for stretched stems.

Sow thinly and thin ruthlessly

Crowded seedlings compete for light and grow tall trying to win. Snip the weaker ones off at soil level with scissors rather than pulling them, which disturbs the roots of the keepers.

Give them a breeze

Brushing your hand over the tray a few times a day, or running a small fan nearby, thickens stems. Then harden off over a week: an hour outside in shade on day one, building up to a full day before planting out.

Spare seedlings are worth something

Nobody needs twenty tomato plants, but twenty neighbours might want one each. Seedlings are one of the things home gardeners can sell — or give away — through HomeGrown™, with pickup just around the corner.