Gadenin日本語Get the appWhat a dormant crocus actually is
Once the leaves have yellowed, what is left in the soil is a new corm sitting directly on top of the shriveled remains of last year's, with a cluster of small cormlets around its base. It has no live roots and it wants to be dry. This is different from a daffodil bulb, which stays fleshy and never truly stops; a crocus corm is a hard, flattened disc that can be handled roughly and stored dry without harm.
It is also why summer wet kills crocus. A corm sitting in ground that stays damp through the warm months rots, and a colony in a bed that is irrigated for summer bedding will thin out over a few seasons no matter how well it flowered at the start. If you water anything over the top of dormant crocus, that is the thing to change.
Leave them in the ground unless there is a reason not to
Crocus are not lifted annually. They are among the easiest bulbous plants to leave permanently in place, and leaving them alone is what produces the spreading sheets they are grown for. Every lift sets a colony back a year while it re-establishes.
There are four reasons to disturb them. The clump has become so congested that it produces plenty of leaves and few flowers. The site turns out to hold summer water and needs to be changed. You are digging that ground over for something else and would rather move the corms than mince them. Or you want to increase your stock quickly by separating the offsets and planting them in a wider area.
In every one of those cases the work is done in dormancy, once the foliage has completely gone and before the corms start rooting again in autumn.
Lifting and dividing a congested clump
Congestion in crocus shows as a dense tuft of leaves with only a handful of flowers, and it typically arrives after five to eight years of good growth. Dividing it gives you several colonies for the price of one.
- Dig wide, and dig in dry weather Put the fork in a good eight inches (20 cm) outside the visible edge of the clump and lever the whole mass up rather than digging into it. Crocus corms sit shallow and travel sideways more than you expect, so a tight circle around the leaf tuft will slice through half the colony.
- Break the mass apart by hand Shake the soil off and pull the corms apart with your fingers. They separate readily. Rub off the shriveled old corm underneath each new one and any loose papery skin, and keep the small cormlets, which are the bulk of your increase even though they need two or three years to reach flowering size.
- Sort by size before you replant Keep flowering-sized corms and cormlets separate. Plant the large ones where you want flowers next spring, and grow the small ones on in a spare corner or a deep pot where you will not be disappointed by a year or two of nothing but leaves.
- Discard anything soft, hollow or moldy A sound corm is firm and heavy for its size. Anything that gives under thumb pressure, is light and hollow, or carries gray or blue-green mold goes in the bin rather than back in the ground. One rotten corm in a replanted group will take its neighbors with it.
- Replant at once if you can Corms go back at three to four inches (8-10 cm) deep and three inches (8 cm) apart, into ground improved with grit if it is heavy. Replanting straight away in summer is better than storing, because a corm out of the ground loses moisture steadily and a shriveled corm flowers poorly.
Do not replant a divided clump back into the exact same footprint at the same density. The whole point of dividing is to give the corms room, so spread them over an area two or three times the size of the original patch, or start a second colony elsewhere in the garden.
Storing corms when you cannot replant at once
If corms have to be held over until autumn, the storage conditions decide whether they flower. They want to be dry, cool, dark and airy, in that order of importance. Trays, paper bags or open net bags all work; sealed plastic does not.
| Condition | What to aim for | What goes wrong otherwise |
|---|---|---|
| Drying before storage | A few days spread out in a dry, airy, shaded spot | Damp corms go moldy within a fortnight |
| Temperature | Cool, around 60-68F (16-20C) | Heat shrivels them; frost destroys them |
| Container | Paper bag, net bag or open tray | Sealed plastic traps moisture and rots the lot |
| Light | Dark or dim | Bright light and warmth start them into growth early |
| Checking | Look through them once a month | One rotting corm spreads through a closed bag |
| How long | Until early autumn at the latest | Corms held beyond that shrivel and flower weakly |
Pots over summer, and what to record
Potted crocus can spend the summer as they are, provided the pot is moved somewhere it will stay dry: under a bench, against a wall out of the rain, or into a cold frame with the lights on. Stop watering entirely once the leaves yellow. The alternative, and usually the better one, is to tip the pot out, take the corms, and plant them into the garden in the autumn, using fresh corms for the pot instead.
Record the date you lifted each clump, how many flowering-sized corms and how many cormlets it produced, and where each portion went. The count is the useful number: it tells you how fast that position is actually multiplying, and after two divisions you will know how many years a clump in your garden takes to go from planting to needing splitting again. Note where the small cormlets were planted, because they will produce nothing but grassy leaves for two springs and you will otherwise be convinced they failed.