Stop harvesting from one plant entirely. It will send up a central stem, branch, and produce small yellow flowers. This takes two to three weeks from the decision to the first flowers.

Watch the seed heads?

After flowering, each head develops a dandelion-like pappus — a fluffy parachute. The seed is ripe when the fluff begins to show and the head starts to open.

Bag before they shatter?

This is the step people skip. Tie a paper bag or a fine mesh bag over the head while it is still tight, then check daily. When the head has opened inside the bag, cut the whole stem and shake the seed into the bag.

Spread the seed on paper in a dry room for a week. Rub gently to separate the seed from the fluff, then winnow by pouring between two bowls in a light breeze.

Ten seeds on damp paper in a warm place for seven to ten days. Seven or more germinating means the lot is good. Store in a sealed jar with silica in the fridge.

Saved seed from this crop?

Germination rates, what came true and what crossed — post it and let other growers learn from it.

Annual, biennial and vegetative crops all save differently. The index compares them side by side.

DarkGrowSeed Bank

← Seed bank

Grow notes

Fourteen crops, one page each

Everything for a crop in one place: the guide, all its varieties with spacing in metres and feet, the seed-saving protocol, and whether your plot can actually isolate it.

Lettuce (110)The fastest crop here and the one to learn on. Bolt resistance is the whole game.10–120 days · 0.05 m–0.61 m spacing Herbs (104)One page, many species — dill, basil and coriander behave nothing alike.16–500 days · 0.05 m–0.91 m spacing Tomatoes (91)Self-pollinating, so seed saving is easy. Heat and calcium are what go wrong.45–90 days · 0.15 m–1.2 m spacing Beans (84)Bush and pole are different plants in practice. Both fix their own nitrogen.45–95 days · 0.08 m–1.8 m spacing Brassicas (79)Biennial for most, so seed takes two seasons and isolation is measured in fields.20–220 days · 0.1 m–0.61 m spacing Peppers (73)Slow to germinate and slow to ripen. Heat at the start decides the whole season.55–112 days · 0.2 m–0.91 m spacing Squash (60)Separate male and female flowers, and bees that travel further than your garden.48–125 days · 0.46 m–29 m spacing Microgreens (57)Cut before flowering, so there is nothing to isolate and no season to plan.2–112 days · 0.03 m–0.25 m spacing Root Vegetables (56)Biennial: the root you eat is not the plant that makes seed.21–120 days · 0.03 m–0.46 m spacing Alliums (44)Onion and leek seed lasts barely a year. Buy fresh, sow thick.50–240 days · 0.03 m–0.3 m spacing Melons (38)The most demanding crop in the catalogue and the least worth the space indoors.60–110 days · 0.46 m–3 m spacing Peas (35)Strictly self-pollinating and cold-tolerant. The earliest useful harvest.37–90 days · 0.05 m–0.2 m spacing Cucumbers (31)Insect-pollinated and bitter when stressed. Hand-pollinate for true seed.49–75 days · 0.15 m–1.2 m spacing Eggplants (29)The slowest nightshade. Needs more heat than tomato and longer to get going.37–90 days · 0.3 m–0.76 m spacing

Questions, answered

Lettuce has the problem pages so far — six of the questions people actually search. The other crops get theirs as the guides are extended.

How to stop lettuce boltingHeat, day length and root restriction, plus 27 varieties with documented bolt resistance. Why is my lettuce bitter?The four causes, what helps, and 21 varieties recorded as mild. Lettuce growing tall and thinEtiolation versus bolting, and 18 compact varieties. Sprouted, then stoppedFive reasons a seedling stalls after cotyledons, in order of likelihood. Growing lettuce indoors all yearLight hours, temperature and 18 varieties that suit a pot. The Kratky methodPassive hydroponics with no pump — and the crops it does not work for.

Reference tables

Isolation calculator14 crops, metres and feet, with a verdict for your plot. Days to harvest by cropFastest, median and slowest, from 891 varieties. Germination timesBy crop, and when to give up on a tray. Free dataset891 varieties as CSV and JSON, CC BY 4.0.