Gadenin日本語Get the appThe flowers finish, and the real work starts
A crocus flower lasts a few days in warm weather and up to two weeks in cold. When it goes over it simply collapses into a papery mess at the base of the leaves and needs no attention at all. There is nothing to deadhead in the sense that there is with a daffodil, and no stalk to preserve; the flower sits almost directly on the corm.
What matters is what happens next. The grassy leaves, each with a distinctive white or silver stripe down the center, keep growing for another four to six weeks after the last flower. During that period the plant is doing the only job that counts: building a completely new corm on top of the old one, and usually a cluster of small offset cormlets around it. Whatever the leaves manage to store in that window is the whole of next spring's flower.
Six weeks of leaves, uncut and unmown
The rule is simple and it is not negotiable: leave the foliage until it has yellowed and gone limp of its own accord. At that point it pulls away with the lightest tug, or can be mown off, and the corm below has finished. Cut it green and you are removing the factory halfway through the shift.
This is where naturalised crocus in a lawn is either a great success or a slow failure, and the difference is entirely down to the mower. Crocus flower very early, which means the six-week wait usually ends around the time everyone else is making their second or third cut of the season. If you cannot leave that section of grass alone that long, plant the crocus somewhere else: under a hedge, in a rough bank, in a bed you do not mow.
| Timing after flowering | What the plant is doing | What you should do |
|---|---|---|
| Immediately after the petals collapse | New corm starting to form on the old one | Feed once; leave everything else alone |
| Two to four weeks after | Leaves at full size, storing hard | No mowing, no tying, no tidying |
| Four to six weeks after | Leaves yellowing from the tips | Still wait; hold the mower off |
| Leaves fully yellow and limp | Corm complete, plant going dormant | Mow or clear; safe from this point on |
| Leaves cut while still green | Corm building stops where it stopped | Expect fewer and smaller flowers next year |
One feed while the leaves are still green
A single application of a balanced or low-nitrogen fertilizer as flowering ends is worth more than anything else you do for a crocus colony. Scatter it over the surface and let the rain take it in. Bonemeal, a general bulb feed, or a tomato-type liquid feed on potted corms all work.
The reason to feed now rather than in autumn is that the plant is only actively taking up nutrients while it is in leaf. Once the foliage yellows, the roots die back and anything you apply sits in the soil until the following winter. Feeding a dormant crocus in summer does nothing except encourage weeds.
Seed heads, self-sowing and letting the colony spread
Some crocus set seed after flowering, producing a small green pod that pushes up on a short stem from the base of the leaves. In a border you can pull these off if you want the plant's energy going into the corm rather than the seed. In grass or in a wild corner, leave them; self-sown seedlings are one of the two ways a colony turns into a sheet.
The other way is offsets. Every year each corm is replaced by a new one and produces small cormlets around its base, which take two or three years to reach flowering size. Left completely alone, a group of fifty corms becomes a dense patch of several hundred within five or six years, and eventually spreads outwards into wide sheets of color that no amount of planting could achieve in one go. Seedlings appear a little away from the parent clump and slowly extend the edges.
This is the strongest argument for planting crocus in grass or rough ground rather than in a tidy border. Borders get forked over, weeded and replanted, and every one of those operations breaks up the colony. Grass that is left alone until midsummer does not.
The corollary is patience. A crocus planting looks thin in year one and merely respectable in year two. The sheets are a five-to-ten-year proposition, and the only way to get there is to do nothing except keep the mower off and feed once a year.
If a naturalised colony is thinning rather than thickening, the cause is nearly always one of three things: the grass is being cut too early, the site is too shady once the trees leaf out, or the ground stays wet through the summer. Check those before assuming pests or exhausted corms.
Record what came back and how wide it got
Write down the date the leaves finally yellowed, because that date is what governs your mowing next year and it is more consistent in a given garden than any general advice about weeks after flowering.
Once a year, note roughly how far each colony has spread: pace it out or photograph it from the same spot each spring. Crocus spread slowly enough that you cannot see it happening from one week to the next, but a note or a photograph from three years ago makes the progress obvious, and it tells you which positions in your garden actually suit them. Record any group that flowered noticeably less than the year before, since that is the one to lift and divide in the summer.