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How to plant a wooden window box once the listing is chosen

Updated: October 2026

The box is already in the hall and the compost is still in the sack. A slatted trough loses soil as soon as you water, and an indoor tray with no holes becomes a puddle if you treat it as a trough. This is how to plant a wooden window box once the listing is chosen: check the base, cover only the large gaps, use peat-free compost, and water the sill you have. The Products Compared editorial team followed RHS container pages and the amazon.co.uk listings saved on 15 October 2026. There is no laboratory test. Which box to buy is on the [wooden window box comparison](/hub/door-and-window-security/wood-window-box).

The box is already in the hall and the compost is still in the sack. A slatted trough loses soil as soon as you water, and an indoor tray with no holes becomes a puddle if you treat it as a trough.

Our top picks

NUPTIO Nuptio white window boxes

Best overall

NUPTIO Nuptio white window boxes
6.4/10about £19.98
View offer
Hortico Hortico 76 cm window box

Rank 2

Hortico Hortico 76 cm window box
8.8/10about £26.99
View offer
Hortico Hortico 51 cm pair

Alternative

Hortico Hortico 51 cm pair
6.7/10about £38.78
View offer
On this page
  1. 1.Check the base before you open the compost
  2. 2.Cover large gaps, then add peat-free compost
  3. 3.Water the sill you actually have
  4. 4.When not to plant this box

Check the base before you open the compost

The open slats are the two Hortico troughs. The 76 cm box is 24.5 litres and 3.5 kg empty. The pair states 14.5 litres. Neither pack includes a liner, and the shared UK reviews say soil leaves the gaps. A liner is required before compost goes in. Sheet versus fabric is on the lining page. Growscape claims a liner, drainage is No, and the size lines include 10 gallons. Do not plant it as a 24.5 litre trough. Tomotato has no holes and is listed as indoor. If the lease or a restrictor is still unchecked, stop at the balcony page.

Cover large gaps, then add peat-free compost

Cover a hole with crocks only when it is larger than about 2.5 cm. The RHS says small holes do not need that layer. Hortico’s slats are wider, so the liner comes first. Use peat-free compost. A multipurpose peat-free mix suits short-term bedding, and a soil-based peat-free mix suits longer-term plants. An England peat sales ban was announced and did not take effect, so this is RHS advice, not a claim that peat compost is illegal to sell. Set the root ball about 5 cm below the rim. These troughs are 15 cm high.
NUPTIO Nuptio white window boxes

Testsieger

NUPTIO Nuptio white window boxes
6.4/10about £19.98
View offer

Water the sill you actually have

The RHS says to feel about a third of the way down and to water if it is dry there. Light rain often wets only the top few centimetres under a roof overhang. South- and west-facing sills dry faster than north- and east-facing ones. Water thoroughly rather than a daily splash. In summer, empty a drip tray within a few hours. Take trays away in winter.

When not to plant this box

Stop if the wood is a vase or a size you cannot reconcile. Nuptio is 8 cm high and ranked under vases. Tbest is 4 × 8.9 × 4 cm at 110 g. About 15 cm with litres stated can take compost. About 7–8 cm suits a pot stood inside the wood. If two size lines still clash, go back to the buying guide before you open the sack. A qualifying amazon.co.uk purchase can earn a commission at no extra cost to you.

Common questions

What do I do first if the wooden box has a slatted base?
Line it before any compost goes in. Both Hortico troughs here are slatted, neither lists a liner, and the shared UK reviews say soil leaves the gaps. A crock on bare slats does not hold the compost. The sheet-versus-fabric choice is a lining job, not a second planting method. Do not drill the slats as a substitute.
Can I plant straight into a box that has no drainage holes?
Not as a soil trough. Tomotato states no holes and indoor use, so pots sit inside and water stays in the wood. Filling that tray and leaving it outside will waterlog the roots. Growscape’s drainage line is No as well, and its size is not a 24.5 litre trough. Drilling either box into a window trough is not the step on this page.
Which compost should I use, now that a peat ban was announced?
Use peat-free compost. A multipurpose peat-free mix suits short-term bedding and veg. A soil-based peat-free mix suits longer-term plants. The announced England peat sales ban did not take effect, so this is RHS advice rather than a ban already in force. Garden soil compacts in a box and is the wrong filling.
How full do I fill the box?
Set the root ball so it sits about 5 cm below the rim, fill around it and firm lightly. That gap stops watering from washing compost over the edge. These troughs are 15 cm high, so the gap is a large share of the depth. Do not add a second publisher’s 2 cm rule on top of the RHS figure. Cover a hole with crocks only if it is larger than about 2.5 cm.
How do I know when a window box needs water?
Push a finger about a third of the way down. If it is dry there, water thoroughly. A damp surface after a shower is not enough, especially under an overhang where rain often misses the sill. South- and west-facing sills dry faster than north- and east-facing ones. Empty a summer drip tray within a few hours, and remove trays in winter.
Which of these wooden boxes should I not plant as a soil trough?
Skip Nuptio for compost, skip Tbest at 4 cm and 110 g, and skip the sub-500 g trays with clashing sizes. Faroby is a little heavier and still about 7 cm high, with no reviews. Stand a pot in a shallow shell if you want the look. The litre-stated 15 cm Horticos are the boxes this order is written for, after a liner.

Related pages

Window boxes through winter

Wooden window boxes

Wooden window box on a balcony or in a rented flat

Best wooden window box for compost or table flowers

Wooden window box buying guide: height, liner, size

How to line a slatted wooden window box for compost

Sources

Public sources used for this comparison. Prices, stars and review counts are amazon.co.uk figures from the listing extracts dated 15 October 2026.

  1. Consumer Rights Act 2015, sections 9 to 11 (retrieved 15 October 2026)
  2. Creosote Regulations 2003 (retrieved 15 October 2026)
  3. HSE biocides overview (retrieved 15 October 2026)
  4. Wood Protection Association, Use Class 3 (retrieved 15 October 2026)
  5. RHS: how to plant up a container (retrieved 15 October 2026)
  6. RHS: roof gardens and balconies (retrieved 15 October 2026)
  7. GOV.UK: how to rent a safe home (retrieved 15 October 2026)
  8. Inveka: drilling into uPVC windows (retrieved 15 October 2026)