Petunias do not grow back after the first cold night. An October box is planted again, but not the way it was in May. A container freezes from every side. A bed does not. That is why a small box on an open railing dies in January while the same plants in the ground by the house wall live.
Depth first, then the plant
| Container | What goes in during October | What to leave out |
|---|---|---|
| Box under 20 cm | Pansies, violas, a low chrysanthemum, ivy, fescue, and at most two ornamental kales in a 60 cm box | Bulbs, garlic, heather, heuchera |
| Pot from 25 cm | Daffodils below and tulips above, or a heuchera and a spindle that are meant to stay | Summer annuals, and a self-watering reservoir through winter |
| A separate pot for heather | Heather, winter heath and checkerberry, ericaceous compost, kept slightly moist | Pansies, and a saucer of hard tap water |
Pansies and violas now, flowers again in spring
Pansies (Viola × wittrockiana) and the smaller horned violet (Viola cornuta) are still worth planting in the first half of October. Buy plants in bud, not leggy ones already in full flower that collapse after the first frost. Space them about 15 cm apart and pinch off spent blooms so they do not set seed. A light frost browns the flower. The crown shoots again in spring if the root ball in the pot did not dry out completely. A 60 cm box holds four pansies and one ivy over the edge, not a row of eight kales.
While the nights stay mild, ornamental kale stays green. Purple and pink come only once the cold is real, and a longer hard freeze finishes it. Do not count on it until spring.
Heather in a pot of its own
Common heather (Calluna vulgaris) wants acid compost and must not dry out. Winter heath (Erica carnea) tolerates a little more lime, but it still hates drought and it hates standing in a saucer. In the same box as pansies it usually fails, because ordinary balcony compost is wrong for it and a window box dries out over a weekend. Give it a separate pot, ericaceous compost, and water so the compost stays slightly moist. Empty the saucer. Checkerberry (Gaultheria procumbens), with its red berries, belongs with the heather. It wants the same compost. Calluna is the one in colour now. Erica flowers in late winter. In October it is still green, and that is fine.
Leave the window as a window
From the street the box should say one thing, and from the room it should still leave the view. Put the tall plant by the frame, not in the middle of the glass. Something low in front of it, and one trailer over the front edge. Do not mix warm and cool colours in the same pot. Burgundy next to orange and silver turns to mud from the pavement.
- If you want it warm. A low chrysanthemum, one kale and ivy over the edge is enough. Lay a rose hip or a rowan berry on the compost, not on the crown. Take them off once they go soft.
- If you want it cool. A white viola, blue fescue (Festuca glauca) and ivy. Silver cushion bush (Calocephalus) is a filler until the first frosts. It will not stay in a Central European box.
Leave heather and checkerberry in that acid pot. They do not belong here.
Heuchera (Heuchera) holds its leaf without a flower, but do not put it in a shallow box if it is meant to live. It wants a pot of at least 25 cm, the same as a spindle (Euonymus). That one hangs over the edge like ivy and stays green through winter. Leave fescue and sedge (Carex) alone for now. The tired clump covers the middle, and you cut it in late winter. Fountain grass with fluffy spikes looks good now, but in a pot it usually does not get through the winter.
A clay pot from the florist that was not fired for frost splits over winter. If the container is staying outside, stick to plastic or wood. Wood keeps the roots a little warmer. Empty a self-watering tank right down now. Ice lifts it and the plastic cracks in a corner. The morning after a frost, throw out only a plant that is soft and black. Leave a browned pansy flower. A chrysanthemum for next year: cut it low, about a hand's width, and keep it in a cool room where it does not freeze. Do not count on it on an open railing through January.
A deeper pot: daffodils below, tulips above
A box 15 cm deep cannot hold a bulb with compost over it and drainage under it. Layered planting needs a pot at least 25 cm deep, 30 cm is better, with a hole in the base. In the first half of October, daffodils go at the bottom. Tulips in a bed wait for cooler soil. In a pot on a balcony the compost cools quickly, so they can go into a pot that will stay outside. Do not bring that pot into a heated room. The bulbs need several cold weeks outdoors, roughly below 10 °C, or they will not flower in spring. Depth in the open ground, and what to do with the leaves after flowering, is in the guide to planting spring bulbs.
- Put 2–3 cm of grit in the bottom. The hole has to stay open. A sealed outer pot with no drainage rots the bulbs.
- Compost, then daffodils nose up, not touching each other or the wall. About 5 cm of compost.
- Tulips one layer higher, noses up again. Another 8–10 cm of compost above them.
- Pansies on top. Their root balls must not spear the bulbs. Crocuses fit in that top layer if 8 cm of compost stays above them.
- Water once so the compost settles. Empty the saucer. Do not feed with nitrogen now.
Where the pot spends the winter
- Against the house wall, not on an open railing. A small box on a metal rail freezes first. A group of pots by the wall holds a little more warmth.
- Raise the pot. The drainage hole must not sit in a puddle and freeze shut. Feet, or two slats, are enough.
- Water on a thaw, when the top is dry. A south-facing balcony in winter sun dries a pot even when the air is cold. Do not water frozen compost. Wait for the thaw.
- When a night around −8 °C is forecast, wrap the pot, not the plants in a plastic bag. Bubble wrap or hessian goes around the pot wall. Pansies can take horticultural fleece for one night. A plastic bag over the leaves cooks them in the sun and holds them wet. Fleece, and what not to cover with plastic, is in protecting plants from frost.
- A box under 20 cm can move to an unheated hallway or garage for a hard frost and come back out when it eases. Not into the living room. That is too warm for the bulbs and too dark for the pansies.
What does not belong in an autumn box
- Petunias and geraniums, in the hope they will sprout again. The annuals are finished. A geranium can be overwintered somewhere cool and on the dry side. That is a different job from planting the box.
- Garlic and onion sets in a shallow box. They belong in a bed. A pot of 30 cm will hold a few cloves, but it is a compromise. The method is in when to plant garlic.
- Heather in the same compost as the pansies. And pure garden soil instead of potting compost. In a pot it packs hard and stops draining.
Onion sets, lamb's lettuce and daffodils for the open bed have their own deadline in what to finish in the first half of October. The rest of this month's planting is in what to plant in October. Summer balcony, aspect and compost are in the balcony garden guide.
Frequently asked questions
Is mid-October too late for pansies?
No. Plant them in bud, not as overgrown flowers. A light frost browns the bloom and the pansy shoots again in spring, as long as the root ball did not dry out.
Can tulips go into a window box now?
Not into a shallow box. Into a pot at least 25 cm deep that stays outside, yes. In a warm room the bulb never gets its cold spell and it will not flower.
Why does heather fail next to pansies?
It wants acid compost and it must not dry out. It does not belong in the pansy box. Give it its own pot, ericaceous compost, and an empty saucer. Checkerberry belongs with it, not a viola.
Is a self-watering box all right in autumn too?
For geraniums in May, yes. Empty the tank now. Frozen water lifts the base and the plastic cracks. An ordinary box with a hole in the base is the safer winter pot.