How do I get hyacinths to flower indoors for Christmas?

Why only prepared bulbs will do it, the dark cold period that has to be counted backwards from the date you want, and the two failure modes that produce leaves and no flower.

Difficulty: beginner
Time: 40 min
Read: 5 min

Short answer

Buy bulbs specifically labelled prepared or treated, plant them in late September, and keep them completely dark and cold — under 9°C — for about ten weeks. When the shoots are 40 to 50mm tall and you can feel the flower bud inside, bring them into a cool light room, then gradually into warmth. Ordinary hyacinth bulbs will not flower at Christmas.

Forcing is simply persuading a bulb that it has been through a winter, in less time than a winter takes. Hyacinths sold as prepared have already had part of that cold treatment applied commercially, which is why they can be brought into flower in December. An ordinary hyacinth bulb has not, and no amount of care indoors will make it flower early.

What you'll need

Prepared or treated hyacinth bulbs
Bulb fibre, or peat-free compost, or a hyacinth glass
A bowl or pot
A completely dark, cold place — cellar, garage, shed or a cupboard in an unheated room
Black bin bag or a box to exclude light (optional)
Gloves

Step by step

Buy prepared bulbs, and check the label.They are sold as prepared, treated or specially prepared, usually from August, and cost slightly more. Ordinary hyacinth bulbs are for garden planting and will flower in spring whatever you do to them.
Count backwards from the date you want flowers.Roughly ten weeks in the dark and cold, then two to three weeks coming into light and warmth. For Christmas, that means planting in the second half of September. Planting in November will not produce flowers in December.
Wear gloves — hyacinth bulbs irritate skin.The bulbs carry crystals that cause itching and irritation in many people. Gloves, and wash your hands afterwards.
Plant with the tips just above the surface.Use bulb fibre in a bowl without drainage holes, or ordinary compost in a pot with drainage. Set the bulbs close but not touching, with the noses just showing. Water so the compost is damp, not wet.
Put them somewhere completely dark and genuinely cold.Under about 9°C. A cold garage, an unheated shed, a cellar or a north-facing outhouse. Cover with a black bag or a box if any light gets in. A warm dark cupboard indoors does not work — it must be cold as well as dark.
Check every couple of weeks.Make sure the compost has not dried out completely and that no mould is developing. Water very sparingly if needed.
Bring them out when the shoot is 40 to 50mm tall.The other test is to feel gently at the top of the shoot for the flower bud inside. Bringing them out before the bud is formed produces leaves and a stunted flower down inside them, which is the classic failure.
Move them into a cool, light room first.Around 10°C for a week or so, in good light. The shoots green up and lengthen. Going straight from a cold dark shed to a warm sitting room shocks them and gives short weak flowers.
Then move them into normal room warmth.They will come into flower over the following one to two weeks. Keep them out of direct sun and away from radiators, both of which shorten the display considerably.
Support the flowers and turn the bowl.Forced hyacinths become top-heavy and lean towards the light. Turn the bowl daily and put in a few short split canes or twigs if the heads flop.
Plant them out in the garden afterwards.Once flowering finishes, cut off the spent flower, keep the leaves watered and fed until they die back, and plant the bulbs out in the garden in spring. They will not force a second time, but they usually flower outdoors in following springs, smaller and later.

Tips

Plant all the bulbs in one bowl at the same depth and use the same variety, or they flower at different times and look ragged.
Hyacinth glasses — the vase-shaped ones that hold the bulb above water — work well and are a good way to watch the roots. Keep the water just below the base of the bulb, not touching it.
Prepared 'Paper White' narcissi are quicker and easier than hyacinths, needing only about five to six weeks and no dark period at all.
Cool is the theme throughout. Forced bulbs kept cool last two or three times as long in flower as ones on a warm windowsill.

Common mistakes

Using ordinary hyacinth bulbs — Without the commercial cold treatment they will not flower until spring, whatever the indoor conditions.
Bringing them into the light too early — The classic result is a stunted flower buried down among the leaves. Wait until the shoot is 40 to 50mm and you can feel the bud.
Using a warm dark cupboard — Darkness alone is not the trigger. The bulbs need cold — under about 9°C — as well.
Putting them straight into a warm room — The abrupt change gives short weak stems. A week in a cool bright room in between makes a marked difference.

If it doesn't work

Leaves growing but the flower is stuck down among them

Cause: Brought into the light and warmth too early — Fix: Put the bowl back somewhere cool and dark for another week or two. It sometimes recovers; often it does not.

Tall floppy leaves, pale and drawn

Cause: Too warm and too dark for too long — Fix: Move to a cool, bright position immediately. Support the growth with canes.

Mould on the compost surface

Cause: Too wet in the dark period — Fix: Scrape it off, reduce watering, and improve airflow. Bulb fibre should be damp, not wet.

Flowers over in a few days

Cause: Too warm, or too near a radiator or direct sun — Fix: Move somewhere cooler. Forced bulbs last far longer in a cool room.

Questions people ask

Can I use ordinary hyacinth bulbs for Christmas?

No. Only bulbs sold as prepared or treated have had the commercial cold treatment that lets them flower in December. Ordinary bulbs flower in spring.

When do I need to plant them?

Around the second half of September for Christmas flowering — about ten weeks cold and dark plus two to three weeks coming into flower.

How cold does the dark period need to be?

Below about 9°C. A cold garage, shed or cellar. A dark cupboard in a heated house is not cold enough.

Can I force the same bulbs again next year?

Not successfully. Plant them out in the garden after flowering and they will usually flower outdoors in future springs instead.