It will not flower
A plant that grows well and never flowers is usually short of light, or short of the trigger its species needs. What each of the common houseplants actually wants.
What it usually is
1 Not enough light
| How to tell | Healthy green growth, good size, no buds, in a spot with no direct sun. Flowering costs far more than leaf making, and a plant that cannot pay simply does not. |
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| The fix | Move it to the brightest position the species will take. For most flowering houseplants that means a window with some direct sun in the morning or late afternoon. Expect the change to take a season rather than a fortnight. |
2 Too much nitrogen
| How to tell | Large, soft, dark green leaves on a plant fed with an all purpose feed through the year, and no buds at all. |
|---|---|
| The fix | Switch to a feed higher in potassium, the kind sold for tomatoes, through the growing season. Nitrogen builds leaves, potassium builds flowers, and a plant given plenty of the first has no reason to attempt the second. |
3 The trigger the species needs has not happened
| How to tell | Look up what your plant needs. Christmas cactus wants long uninterrupted nights and cool weeks in autumn. Moth orchids want a drop of about ten degrees between day and night for a fortnight. Bulbs want a cold rest. Nothing you do about light or feed substitutes for these. |
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| The fix | Give it the trigger deliberately. Move the orchid to a cooler room or nearer a window at night in autumn. Put the Christmas cactus somewhere genuinely dark from evening to morning for six weeks. Then return it and wait. |
4 The plant is too young, or too comfortable
| How to tell | A young plant that has never flowered, or one repotted recently into a much larger pot and now growing vigorously. |
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| The fix | Wait, and stop potting on. Many species flower only when the roots are snug, and a plant given room to grow will grow rather than flower. Leave it in the same pot for another year. |
Through the year. Most houseplants set buds in response to the lengthening or shortening of the day, so the work is done months before the flowers appear. Autumn conditions decide a winter flowering, and winter light decides a spring one.
Flowering is expensive. A leaf pays for itself over its life; a flower never does, in energy terms, and a plant only attempts one when it has a surplus and a reason. Almost every case of a healthy plant that will not flower comes down to one of those two being missing.
The surplus is light, and this is where most indoor flowering fails. A plant that makes decent leaves in a north facing room has enough light to live and not enough to bloom. There is no feed, no fertiliser and no trick that substitutes for it. If you want flowers from a plant indoors, it needs the best window in the house, and for most species that means real sun for part of the day.
The reason is the trigger, and it differs by species in ways that are worth looking up rather than guessing. A Christmas cactus sets buds when the nights are long and unbroken and the room is cool, which is why one standing under a lamp that is on until midnight never flowers. A moth orchid sets a spike after a fortnight with about ten degrees between its warmest and coolest hours, which is what an autumn windowsill provides and a centrally heated hallway does not. An amaryllis wants a dry rest. A hoya wants to be left alone on the same spur, which is why cutting off the old flower stalk costs you next year’s flowers.
Feeding is the third piece and the easiest to get backwards. All purpose feeds are built around nitrogen, which grows leaves. A plant you want flowers from wants potassium, and the cheapest source is ordinary tomato feed, used at the strength on the bottle from spring until the flowers open.
Last, patience and pot size. Many houseplants flower better slightly potbound, because a plant with room to grow will always choose growing. If yours has just gone into a pot two sizes up and is throwing out leaves, that is your answer, and the fix is to leave it alone for a year.
Entries that name it
What the journal says about this symptom on each plant.
| African violet | Not enough light, a pot that is too big, or too much nitrogen. Give it ten to twelve hours of bright indirect light, keep it in a small shallow pot, and use a feed made for African violets. |
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| Agapanthus | Too much shade, too much nitrogen, or a clump divided too often. Move it into full sun, feed with potash rather than a general fertiliser, and then leave it alone. These flower best when pot bound or congested. |
| Amaryllis | A bulb that was not fed and watered through the summer after it flowered. Keep the leaves growing all summer with a fortnightly feed, then give it a dry rest of eight weeks in a cool dark place before starting it again. |
| Bird of paradise | Too little light, a plant that is not yet mature, or a pot that is too large. Move it to full sun, feed through the growing season, and leave it potbound. A seed grown plant needs four to six years and a division two or three. |
| Blackcurrant | Big bud mite, which swells the buds over winter and carries reversion virus. Pick off and burn the fat round buds in winter. A bush that has stopped cropping and has odd narrow leaves has reversion and should be dug out. |
| Bougainvillea | Too much water, too much nitrogen, or too big a pot. Let it dry between waterings, feed with potash, and pot it back down. A slightly stressed bougainvillea is a colourful one. |
| Cape leadwort | Too much shade, or a hard prune done too close to the flowering season instead of at the end of winter. Move it to full sun if the site allows, and save the hard cut for late winter, before new growth starts, so it does not remove the wood the coming flowers grow from. |
| Chilli and sweet pepper | Not enough warmth or light, or a plant fed too much nitrogen. Move it into the warmest brightest place you have and switch to a potash rich feed. |
| Christmas cactus | The plant has not had the long dark nights and cool weeks it needs to set buds. From about six weeks before you want flowers, give it twelve to fourteen hours of complete darkness each night and keep it near 15 degrees, watering sparingly. |
| Clivia | No cool dry rest over winter, or a plant that has just been divided. Stop watering from late autumn and keep it cool for about eight weeks. A divided clump commonly takes two or three years to flower again. |
| Common jasmine | Pruned at the wrong time, or fed too richly. Prune straight after flowering, not in spring, because the flowers come on wood made the previous year. Swap a general feed for a potash rich one. |
| Cosmos | Rich soil or a general feed, which cosmos answers with foliage. Stop feeding and let the ground dry a little between waterings. Pinch the growing tips out once when the plant is thirty centimetres tall to make it branch. |
| Crown of thorns | Not enough light, or too much water and nitrogen. Move it into full sun, feed with potash rather than a general feed, and let it dry properly between waterings. |
| Daffodil | Blindness from a clump that has become congested, or from leaves cut off too early. Lift and split the clump once the leaves have died back, and never knot or mow the foliage for six weeks after flowering. |
| Dahlia | A plant fed with nitrogen, or one never stopped when young. Pinch out the growing tip above the third pair of leaves to make it branch, and switch to a potash feed. Deadhead down to the next bud, not just the flower. |
| Escallonia | A hard prune done in early spring, which removes the previous season's wood before it has flowered, or too much shade. Move the pruning to straight after flowering finishes from now on, and check the site gets a genuinely full day of sun. Both are more common causes than a pest or nutrient problem. |
| Flaming Katy | Too much light in the evenings, because this plant sets buds on short days. Give it fourteen hours of complete darkness a night for six weeks in autumn. A cupboard each evening is the usual method. |
| Flamingo flower | Not enough light, or a pot much larger than the roots. Move it to bright indirect light and leave it slightly potbound. A feed higher in phosphorus through spring and summer helps once the light is right. |
| Geranium | Too much nitrogen, too little light, or a pot several sizes too big. Move it into full sun, swap to a potash rich feed, and pot it back down into something snug. Deadhead by snapping the whole flower stalk off at its base. |
| Green beans | Cold nights, or a plant sown too early. Beans need warm soil. Sowing a fortnight later into warm ground beats sowing early into cold. |
| Hyacinth | A bulb that flowered indoors last year and was not fed afterwards. Feed while the leaves are green and plant it out in the garden in autumn. Forced bulbs take a year or two to build a proper spike again. |
| Hydrangea | Last year's buds cut off in an autumn tidy up, or killed by a late frost. Prune only in spring, taking the old flower heads back to the first fat pair of buds. On mophead types the flowers come from wood made the previous summer. |
| Laurustinus | A hard prune at the wrong time of year, since it flowers on the previous season's wood, or a heavy nitrogen feed pushing leaf growth instead of flowers. Prune only straight after flowering finishes, and skip the fertiliser if the soil is already reasonable. An established plant needs very little of either to flower well. |
| Lavender | Too little sun, too much feed, or a plant that was cut back too hard into old wood. Full sun, no feed, and a light prune each year straight after flowering rather than a hard one in spring. |
| Moth orchid | Not enough light, or no drop in night temperature to trigger a spike. Move it to a brighter window, and give it a few weeks in autumn where nights are about 5 degrees cooler than days. |
| Peace lily | Not enough light, or a plant that is too young. Move to brighter indirect light; mature plants flower in spring and again in late summer. |
| Peas | Too much nitrogen, or too little sun. Stop feeding and move them into full sun. Peas fed with a nitrogen rich feed make foliage instead of pods. |
| Petunia | A container plant that ran out of food, which happens by about six weeks in. Start a fortnightly high potash feed and cut the whole plant back by a third. It will flower again within two weeks. |
| Purple coneflower | A young plant in its first year, or a clump crowded out by neighbours. Give it a season. Plants raised from seed usually flower in their second year, and a clump swamped by taller perennials needs moving to the front. |
| Radish | Nothing to fix. A radish that flowers has been left too long. Pull them at four weeks. A radish left in the ground goes woody and then bolts. |
| Raspberry | Summer fruiting canes cut down in the wrong winter. Learn which type you have. Summer kinds fruit on last year's canes, so cut only the ones that have just fruited. Autumn kinds are cut to the ground in late winter. |
| Rosemary | Too little sun, or too much feed and water. Full sun and leaner treatment. Rosemary flowers best when it is slightly hungry and dry. |
| Scarlet sage | Sown too late, or grown in shade where it never gets warm enough. Move it into sun and be patient, because this one needs heat to colour up. Sow earlier under cover next year. |
| Spider plant | A pot with too much room, or too much feed. Leave it slightly potbound and halve the feed. Spider plants throw runners when they are comfortable but not indulged. |
| Strawberry | A plant more than three years old, or one that has put its energy into runners. Replace plants every three years from their own runners, and cut runners off the plants you want fruit from. |
| Sweet pea | Seed pods left on the plant, which tells it the year is over. Pick or deadhead every single day. One row of pods setting will stop a plant flowering within a fortnight. |
| Sweetheart hoya | Too little light, or the old flower spurs cut off. Move it brighter and never remove the short woody spurs the flowers came from, because the next year's flowers come from the same place. |
| Tomato | Too little light, or too much nitrogen feed. Move it into full sun and switch to a high potassium tomato feed once the plant is growing well. |
| Tulip | Bulbs that were planted too shallow, or left in wet summer soil. Plant at least fifteen centimetres deep, and lift the bulbs after the leaves die back if your soil stays damp through summer. |
| Wax plant | Not enough light, a plant that is too young, a pot that is too large, or the flower stalks having been cut off. Move it to bright indirect light, leave it potbound, and never remove the short woody stalks the flowers came from, because the next year's flowers come from the same ones. |
Questions from the margin
- Why won't my houseplant flower?
- Almost always light. Flowering costs far more than making leaves, and a plant that grows well in a dim room has enough light to live on and not enough to bloom. No feed substitutes for it.
- What feed makes houseplants flower?
- Something higher in potassium than nitrogen, which is what ordinary tomato feed is. All purpose feeds are built around nitrogen, which grows leaves, and a plant given plenty of it has no reason to attempt flowers.
- Why won't my orchid flower again?
- Moth orchids set a spike after about a fortnight with roughly ten degrees between day and night. A centrally heated room never gives them that, which is why an orchid moved to a cooler spot or nearer a window in autumn so often reflowers.
Checked against RHS, Orchids: encouraging reflowering; RHS, Schlumbergera: getting them to flower.