Gadenin日本語Get the appThe shape of the sedum year
Sedum asks for almost nothing, and the few jobs it does need fall at precise moments. Miss the early summer cut back and a tall clump flops for the rest of the season with nothing you can do about it. Divide at the wrong time and you lose a year of flowers. Everything else is a matter of not interfering.
The table below covers both habits through the year. Where the two want different treatment, both are given, because the commonest mistake is applying border-plant maintenance to a creeping mat or the reverse.
| Season | Tall upright types | Creeping mat types |
|---|---|---|
| Early spring | Cut down last year's dead stems. Divide congested clumps | Clear winter debris off the mat. Replug bare patches |
| Mid spring | Watch for slugs on emerging shoots | Growth restarts. Pull out weeds while you still can see them |
| Early summer | Cut every stem back by a third to a half | Take rooted pieces to spread it further |
| Midsummer | Buds forming. No water, no feed | Some types flower now. Nothing to do |
| Late summer | Flower heads color up. Check for aphids | Trim any runners heading where you do not want them |
| Autumn | Flowering peaks then fades. Leave the heads standing | Sweep fallen leaves off the mats |
| Winter | Leave the stems. No water at all | Nothing. Keep pots out of the rain |
Early spring: cut down and divide
Last year's stems on a tall type have stood all winter and now hide the new buds. Cut them off at ground level with pruners, taking care not to snap the fat pink or gray buds pushing up beside them. This is also the only sensible moment to divide, while you can see exactly how many buds each piece is taking with it.
On creeping mats, the work is clearing rather than cutting. Lift off any blanket of tree leaves, sweep out the accumulated grit and debris, and pull away any brown sections that have rotted under the litter. Push rooted pieces from the edge of the mat into the gaps left behind and they will close over by early summer.
Early summer: the cut back that stops the flop
This is the one job on the calendar that changes the whole look of the plant, and it applies only to the tall types. Do it before flower buds are visible, when stems are about eight to twelve inches (20 to 30 cm) tall.
- Judge the timing by height, not date Once stems reach roughly two thirds of their eventual height and before any flat bud clusters appear at the tips, they are ready. Too late and you cut off the flowers.
- Take a third to a half off every stem Cut just above a pair of leaves. Do the whole clump evenly rather than a few stems, or you get an uneven, lopsided plant.
- Use the tops as cuttings Every piece you remove is a viable cutting. Strip the lower leaves, dry the ends for a day or two, and insert them into gritty potting mix.
- Expect a shorter, later, better plant It branches from below the cuts, so you get a sturdier clump around a hand shorter, with more but smaller flower heads, opening a week or two later. It stands up on its own.
If a clump has flopped in past years despite full sun and no feeding, this cut back is the answer, and it needs repeating every year. It is not a one-off correction.
Autumn and winter: leave it alone
The temptation in autumn is to tidy the faded flower heads away. Resist it. The dried heads of tall sedum hold their shape through frost and snow better than almost any perennial, they look genuinely good all winter, and the hollow stems shelter overwintering insects. More practically, the standing stems mark exactly where the crowns are, so you do not put a fork through them in a spring planting session.
Cut nothing on the creeping types at any point. They are evergreen or nearly so, and the only autumn task is keeping fallen leaves off them, since a mat sitting under wet leaf litter for three months rots in patches. Stop all watering everywhere once the weather turns cold, and stand containers where winter rain cannot reach them.
Feeding, or rather not feeding
There is no point in the year at which sedum in reasonable soil needs a fertilizer. Every symptom people try to fix by feeding, floppy stems, pale leaves, poor color, is either caused by feeding already or by a shortage of light. A container plant repotted into fresh compost every two or three years has more than it needs.
The one exception is a plant that has been in the same pot for many years and has visibly shrunk. In that case repot into fresh gritty mix in early spring rather than adding fertilizer, which addresses the exhausted structure of the compost as well as the nutrients.
What to write down this year
Three notes make next year's decisions for you. Record the date you cut the tall clumps back and how they stood afterwards, so you can shift the timing a fortnight if they still leaned. Record the date each clump came into flower, which tells you how much the cut back delayed it. And record the position of every clump and how many hours of sun that position gets at midsummer, because when a plant disappoints, the position is almost always the reason and it is the one thing you cannot reconstruct from looking at the plant in spring.