Window box winter care: saucer off before frost

The first hard frost is on the glass, and the window box is still standing in last week's rain. The saucer is brimful, the compost is cold, and the uPVC sill was never built as a planter stand. Window box winter care, for a box you have already chosen, is one dry half-hour: take the saucer off, raise the box so the holes stay open, and water an evergreen only when the compost is dry. Feed stays in the shed until the days lengthen.

This page is from the Products Compared editorial team. We used Royal Horticultural Society container pages, a Garden News note on uPVC sills, the Creosote Regulations 2003, and Health and Safety Executive guidance on biocides, gathered on 15 October 2026. We grew no season with the amazon.co.uk boxes named here. Prices are those listings. A qualifying purchase through our links can earn us a commission at no extra cost to you.

In short

Before winter, remove the saucer, raise the box so the drainage holes stay clear, and keep the compost out of standing water. Evergreens can still need a drink in a dry spell, and winter feed waits. Leave the uPVC sill undrilled, and leave creosote off the timber.

Take the saucer off and keep the holes clear

The Royal Horticultural Society says to take trays and saucers off before winter so the compost does not stand in water. Waterlogging rots roots. In summer, empty a saucer within a few hours of watering. From the first frost, that tray stays in the shed, including the one packed with a plastic trough.

A Bamworld set of three 16 inch black ABS boxes was £23.74 on the amazon.co.uk listing used here, with a 4.8 rating from 49 reviews. It lists three drainage holes, a removable saucer, and a capacity of 3.8 litres. Store the saucer. We did not winter that set, so the price is not a survival claim. The window box comparison sets it beside the other troughs on drainage, trays, and material. The top pick there is the ARTKETTY 30 cm ceramic trough at about £18.99, with one drainage hole and a removable saucer.

Raise the box on feet or two bricks so the holes stay open. Where a gap is wider than about 2.5 cm, mesh holds the compost in while water still leaves. A plug that seals the hole puts the box back in a puddle. If a stream runs out when you tip it, move it under cover until it drains.

Peat-free compost is the RHS choice. An announced sales ban in England did not take effect, so this page does not treat a ban as law. The mix still waterlogs if the saucer stays on.

Water evergreens, and stop feeding

Evergreens and conifers can still need water in a dry winter spell. The RHS says to check them at least weekly if they are under cover and missing the rain, and to water when they need it. Lift any fleece, press a finger about two centimetres into the compost, and water only if it is dry there. A north-facing box can stay wet for a fortnight, so the weekly check is a look, not a fixed mug.

The RHS winter container page says not to feed. A liquid feed in December pushes soft growth into the next frost. Winter pansies get water when the compost is dry, and the bottle stays shut until the days lengthen. Treat a grey woody herb as dormant, and check the leaves that stay green.

When water sits on the surface for more than a minute, the compost is already full. When it runs straight through a shrunken root ball and out of the holes in seconds, the drink never reached the roots. Stand that second box in a tray indoors for about half an hour, then take the tray away. A reservoir you cannot empty is a poor partner in cold rain. The self-watering and drainage page compares those mechanisms with a plain hole.

Frost, fleece, and a box that can leave the sill

Roots in a box are more exposed to cold than roots in the ground, which is the RHS point. A south-facing wall can shelter them. An upper sill on a north wall cannot. Heavier horticultural fleece is about 2°C of protection in the RHS glossary. That margin will not turn summer bedding into a hardy shrub, and fleece over a full saucer still rots the roots.

Tie the fleece so it is not a sail, and lift it on a mild wet day so the crown can dry. Plastic is not frost-proof just because it is plastic. The RHS winter page says to choose frost-proof terracotta, plastic, fibreglass, or wood, and to raise the pot so freeze-thaw is less likely to crack it. Wet compost expands as it freezes. If you can lift the box, a shed or a porch for a hard week beats an upper sill.

We do not claim that any named amazon.co.uk trough in this batch survived a winter. Let frozen compost thaw on its own, with no hot water and no feed. Brown, mushy crowns are the loss. A limp plant may recover over a mild fortnight.

Wood in winter is not a creosote job

A wooden window box spends winter as timber in the rain. Use Class and BS 8417 are not stated on these wooden listings, so both stay off the product claim. A rustic stain in the photograph is a finish you can see, and it is not a durability class.

Creosote stays off the box. The Creosote Regulations 2003 bar amateur use, and the Health and Safety Executive points the public to biocides allowed for public use. A review that names a creosote-style tin is not a method. This page gives no dilution and no timetable. If the timber needs a finish, use a preservative sold for outdoor garden wood and follow that label on a dry day, while you can still turn the box.

The Hortico pine box is listed at 76 by 23 by 15 cm, 24.5 litres, and 3.5 kg, at £26.99, with a 4.6 rating from 100 reviews, on the amazon.co.uk listing held for 15 October 2026. The base is slatted, and no liner is included. A yearly reseal in some buyers' guides is their interval, not a tested gap for this Hortico. Bare grain on the top edge is the moment for that outdoor finish, before the box is full. Sizes and timber claims are in the wooden window box comparison.

A sheet under the slats stops the drainage. Feet keep the underside out of a film of water, which is what opens the joints by spring.

The sill, the restrictor, and when to move the box

Leave the uPVC sill undrilled. Garden News warns against drilling one, because the hole lets rain into the frame and outlasts the plants. Leave the trough off the window frame as well. Sodden compost makes that pine box a two-hand lift. Move it before a gale.

If wind is the problem, use a patio, a spare ground-floor ledge, or a night indoors. Some council guidance tells tenants not to remove restrictors, and this page does not tell you to remove one. A trough or a wad of fleece against the arm stops the opening the restrictor is there to limit. Shift the planter so the arm can still move.

Keep the box off an escape window. A trough or a stack of bricks on an opening you would climb through is the wrong winter storage. A roof window has its own rules on opening size and sill height, and a planter does not meet them. Balcony edges and leases are on the balcony page. Planting order stays on the planting page.