GrowingHQ

Bulbs, corms, rhizomes and tubers

18 plants sold under one word and covering 5 different storage organs. 12 are planted once and left; 6 have to be lifted every autumn, and the packet rarely says which is which.

The division that loses people their plants

Daffodils, snowdrops and crocuses go in once and increase on their own for decades. Dahlias, cannas, gladioli, begonias and tigridias are a yearly commitment: lifted after the first frost blackens the top, dried, stored somewhere frost-free, and replanted in spring. They are sold from the same rack in the same kind of packet, and the difference is the whole of whether you still have the plant next June.

The two halves also flower at opposite ends of the year, which is why the division is easier to miss than it should be. The hardy ones are mostly spring: bought in September, in the ground by November, over by May. The tender ones are the summer and autumn display, bought in spring and planted after the last frost — so a gardener who only ever shops in autumn meets one group and never the other.

Plant once, or lift every year

Read this before anything else on the page. It is the only fact here with a deadline attached.

Hardy in the ground — 12

Generally survive a British winter where they are planted. Worth saying carefully: this is a claim about the modelled UK context and not a guarantee for every garden. Drainage does more damage than temperature over a British winter — most borderline losses are rot in cold wet ground rather than freezing — so a heavy waterlogged site can still lose plants this column calls hardy.

Lift and store — 6

Not reliably hardy in the ground. Each profile carries the lifting instruction, which is the only thing a reader actually needs once they know this. In a mild, sharply drained garden some gardeners leave them out under a deep mulch and get away with it most years — “most years” being the operative phrase.

Four organs, four ways of handling them

Indistinguishable from outside in some cases, and completely different in what they do underground.

Bulb, corm, rhizome and tuber comparedFour underground storage organs drawn in section at the same scale. A true bulb is layered scales around a growing point on a flat basal plate, and multiplies by offsets that pull apart by hand. A corm is a solid swollen stem base with a bud on top, the previous year's spent corm beneath it and small cormlets at its sides. A rhizome is a horizontal swollen stem that sits at soil level with roots below and a growing point at one end, and must not be buried. A tuber is a swollen stem with growth buds scattered over its whole surface and no basal plate, so a cut piece without a bud on it cannot grow.True bulbbasal plateDaffodil, tulip, lilyPull offsets apart by hand.Cormspent corm below, cormlets asideCrocus, gladiolus, crocosmiaReplaced yearly by a new one on top.Rhizomesoil level — top stays exposedBearded irisCut with a knife. Must not be buried.Tuberbuds scattered, no basal plateCyclamen, potatoA cut piece without a bud will rot.
All four are sold as 'bulbs'. The differences are internal, which is why they are drawn rather than photographed — and each one changes what you physically do with the thing in your hand.
How deep to plant a bulb, drawn to scaleEight geophytes drawn at one scale against a soil surface line, each at the depth the catalogue records for it. A bearded iris rhizome sits on top of the soil with only its roots buried. A cyclamen tuber and a nerine bulb are barely covered, at 2 to 3 centimetres, the nerine with its neck standing proud. Snowdrops and crocuses go at 8 to 10 centimetres, a daffodil at 10 to 15, a tulip at 15 to 20 and a lily deepest at 15 to 25 centimetres. Most sit at roughly two to three times their own height, and the shallow exceptions are shallow because the organ must bake in the sun to flower.soil surface5 cm10 cm15 cm20 cmBearded irison topon the surfaceCyclamen2 cmjust coveredNerine2 cmneck proudSnowdrop9 cmCrocus9 cmDaffodil13 cmTulip18 cmplant deepLily20 cmstem roots
Two to three times the bulb's own height is the working rule, and the four plants that break it are the four most often planted wrong. A bearded iris buried by mulch or a tidy neighbour will make leaves for years and never flower again.

Rhizome — 2

Tuberous root — 1

Bulbs in pots

The one group where a container is often better than the ground rather than a compromise.

The drainage suits them, the display can be moved to where it is actually seen in March and moved out of the way while the foliage dies down, and squirrels are far easier to defeat on a hard surface than in a border. The one rule that still applies: do not cut the leaves off after flowering. The bulb rebuilds itself from them, and a pot tidied in May is a pot of nothing next year.

12 good in containers
PlantStorage organWinter in the groundIn a container
CannaRhizomeliftGood in a container long-term
CrocusCormleave inGood in a container long-term
DaffodilTrue bulbleave inGood in a container long-term
DahliaTuberous rootliftGood in a container long-term
Grape hyacinthTrue bulbleave inGood in a container long-term
Hardy cyclamenTuberleave inGood in a container long-term
HippeastrumTrue bulbliftGood in a container long-term
HyacinthTrue bulbleave inGood in a container long-term
LilyTrue bulbleave inGood in a container long-term
NerineTrue bulbleave inGood in a container long-term
Tuberous begoniaTuberliftGood in a container long-term
TulipTrue bulbleave inGood in a container long-term

The ones that spread on their own

Naturalising is the difference between a planting that thins each year and one that thickens.

It only happens if the leaves are left to die back completely. In grass that means not mowing for at least six weeks after flowering — the corm or bulb is rebuilt entirely from what the leaves make, so an early first cut is exactly why a naturalised drift gets thinner instead of thicker.

Bulbs for shade

Most spring bulbs flower before the tree canopy closes, which makes woodland shade far less of a constraint than it looks.

Ready-made lists from this group

Filtered on the storage-organ and hardiness fields rather than on the word on the packet.

Every bulb, corm, rhizome and tuber

18 plants
PlantStorage organWinter in the groundIn a container
Bearded irisRhizomeleave inNot a realistic container plant
CannaRhizomeliftGood in a container long-term
CrocosmiaCormleave inWorkable in a container, with conditions
CrocusCormleave inGood in a container long-term
DaffodilTrue bulbleave inGood in a container long-term
DahliaTuberous rootliftGood in a container long-term
GladiolusCormliftWorkable in a container, with conditions
Grape hyacinthTrue bulbleave inGood in a container long-term
Hardy cyclamenTuberleave inGood in a container long-term
HippeastrumTrue bulbliftGood in a container long-term
HyacinthTrue bulbleave inGood in a container long-term
LilyTrue bulbleave inGood in a container long-term
NerineTrue bulbleave inGood in a container long-term
Ornamental alliumTrue bulbleave inWorkable in a container, with conditions
SnowdropTrue bulbleave inWorkable in a container, with conditions
Tiger flowerCormliftWorkable in a container, with conditions
Tuberous begoniaTuberliftGood in a container long-term
TulipTrue bulbleave inGood in a container long-term

Know the position rather than the plant? What can I grow? takes your light, soil, space and month and answers from this same catalogue — including which bulbs it rules out for you and why.