Gadenin日本語Get the appThe autumn pot plant is a forced crop, not a garden plant
The tight domes of color sold everywhere in autumn were grown in a greenhouse under blackout cloth to bring the flowering forward, and sprayed with a growth regulator so they stay short and dense on the bench. Everything the plant had went into that one flush of bloom. The root ball is a solid mat filling a small pot, and it is arriving in your garden at the point in the year when soil is cooling and root growth is slowing to nothing.
Planted then, it will finish flowering and go into winter with almost no roots outside its original root ball. Water in the surrounding soil never reaches it, frost heave lifts the shallow plug, and by spring most of them are dead crowns. This is not bad luck and it is not a hardiness problem: the same species planted in spring survives the same winter without protection.
So treat an autumn pot mum for what it is, which is a seasonal decoration, and buy your permanent plants in spring instead, as small rooted plants or divisions. The spring plant will be taller, looser and less uniform than the forced dome, because the growth regulator is not in it. That is the plant behaving normally.
| Item | Autumn pot mum in bud | Spring planted mum |
|---|---|---|
| Root system at planting | Pot bound plug, no new roots forming | Small but actively growing into the bed |
| Weeks of root growth before winter | Two or three at best, in cooling soil | Twenty or more, through the warm season |
| Growth regulator in the tissue | Yes, so it will look different next year | No, natural height and habit |
| Typical winter survival in the open ground | Poor | Good, and improves each year |
| Flowers the year you plant it | Immediately, then nothing | In autumn, after a full season of growth |
Site: full sun, drainage, and nothing overhead
Give a chrysanthemum at least six hours of direct sun. In less it still grows, but the stems stretch, the flower count drops sharply and the plant needs staking it would not otherwise need. Morning sun matters more than late afternoon sun, because it dries the foliage early and keeps leaf spot down.
Drainage is the thing that decides whether a plant lives through winter. Chrysanthemums are not killed by cold nearly as often as they are killed by a crown sitting in cold standing water from late autumn onwards. On heavy clay, raise the planting position by three or four inches (8 to 10 cm) with compost and grit rather than digging a deep hole that fills like a bucket.
Before you plant, look up and look around at night. Chrysanthemums form their flower buds in response to lengthening nights, and a street lamp, porch light or security light shining on the bed after dark will delay flowering or stop it entirely. Choosing a dark corner of the garden at planting time is far easier than moving an established clump later.
Walk the intended bed after dark before you dig. If you can read a plant label there without a torch, the spot is too bright for reliable autumn flowering and you should plant somewhere else.
Spacing, depth and getting it away
Set plants 18 to 24 in (45 to 60 cm) apart. That looks absurd for a rooted cutting the size of your hand, and it is correct: a pinched plant finishes the season as a mound 2 ft (60 cm) across, and crowded plants get leaf spot and mildew in the still, damp air at the center of the group.
Plant at the same depth the plant was growing, with the crown level with the surrounding soil. A chrysanthemum buried an inch too deep rots at the crown over winter. Firm the soil around the root ball with your knuckles rather than stamping it, then water in heavily even if rain is forecast, to settle soil against the roots.
- Fork compost through the whole bed, not the hole Two or three inches (5 to 8 cm) of compost worked into the top spit across the bed. Chrysanthemum roots run wide and shallow, so enriching one planting hole does very little.
- Plant into warm soil once hard frost is past Aim for soil around 55F (13C). There is nothing to gain from planting into cold ground, and a late frost will burn soft new growth on a plant that has just moved.
- Set the crown level and space at 18 to 24 in (45 to 60 cm) Level crown, generous spacing. Both of these are decided in the first minute and are effectively impossible to correct later without lifting the plant.
- Water in, then mulch clear of the stems A gallon per plant to settle the soil, then two inches (5 cm) of mulch kept an inch clear of the crown so the base stays dry and airy.
- Pinch out the growing tip once it is clearly growing Wait for visible new leaves, which means roots have taken. Then remove the top inch to start the branching. Do not pinch a plant that is still sulking after the move.
What to write down on planting day
Record the position of each plant in the bed and the date you planted it, along with whether it went in as a division, a cutting or a bought plant. Chrysanthemums are lifted and split every year or two, and a clump moves a little each time it is replanted, so a bed loses its plan quickly if nothing is written down.
Also note how dark the spot is at night and which plants sit nearest to any light source. When one plant in a row flowers three weeks after the others in the same bed, that note is what tells you it is the light and not the soil, the feeding or the season.