Broad end down, pointed end up, and expect two to eight weeks before anything visible happens. The water and toothpick method works, but planting directly in soil works at least as well.
The toothpick method
- Clean the seed of all flesh, but do not scrub off the brown seed coat.
- Push three or four toothpicks into the sides at a slight downward angle, about a third of the way up.
- Rest the toothpicks on the rim of a glass so the broad end sits in water and the top two thirds stay dry.
- Keep the water level topped up and change it weekly.
- Put the glass somewhere warm and bright but out of direct sun.
The seed will split down the middle first, then send a root down, then a shoot up. The split alarms people who assume the seed has spoiled. It is the expected first step.
The soil method, which is less popular and works better
Plant the seed with the top third above the surface in a pot of free-draining compost, keep it warm, and water when the surface dries. It produces sturdier roots because they never have to convert from water to soil, and the plant is measurably stronger at the same age. The only thing it lacks is the visible progress that makes the water method appealing.
Where most attempts actually fail
Not at germination but afterwards. Two mistakes account for most losses.
- Leaving it in water too long. Once the root is a few centimetres, the seed needs nutrients that water does not supply. Pot it up.
- Never pruning. An unpruned seedling grows into a single bare stem with a tuft at the top and then flops. Cutting it back to about fifteen centimetres when it reaches thirty forces branching and produces a plant rather than a stick.
What you will and will not get
You will get an attractive foliage houseplant that grows quickly and tolerates ordinary indoor conditions. You will almost certainly not get fruit. Seed-grown avocados take many years to reach maturity, need cross-pollination, and do not inherit the parent’s characteristics, which is why orchards graft rather than sow. Treating it as a houseplant project rather than a fruit project makes it a success rather than a disappointment.