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How to plant a hydrangea in compost: depth and water

Updated: October 2026

You have a hydrangea, a bag of compost and a space, but the decisions that matter happen before the bag goes into a hole. How to plant a hydrangea with compost means checking whether open ground suits the colour you want, setting the old compost line level with the soil, and watering through the first season. One sack will not turn chalk into lasting acid ground, and planting deeper will not make the shrub more secure. Our [hydrangea soil comparison](/hub/fertiliser-soil-and-bark-mulch/hydrangea-soil) covers the ericaceous bags. This page is the planting job: ground or pot, hole size, mulch, and when a soil test is more useful than another product.

You have a hydrangea, a bag of compost and a space, but the decisions that matter happen before the bag goes into a hole.

Our top picks

SIC SIC Ericaceous 50 L

Best overall

SIC SIC Ericaceous 50 L
9.2/10about £12.49
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Green Haven Green Haven Ericaceous 50 L

Rank 2

Green Haven Green Haven Ericaceous 50 L
9.4/10about £12.49
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ecoblaze TerraGrade Ericaceous 50 L

Best value

ecoblaze TerraGrade Ericaceous 50 L
8.4/10about £9.99
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On this page
  1. 1.When the bag belongs in a pot, not the hole
  2. 2.Set the depth and width of the hole
  3. 3.Water and mulch through the first season
  4. 4.What compost cannot fix after planting

When the bag belongs in a pot, not the hole

If you have a colour-changing mophead or lacecap, want blue flowers, and garden on alkaline or chalky soil, the RHS route is a container of ericaceous compost. A hole lined with acid medium is only a temporary pocket. The bag does not have to be ericaceous merely because the plant is a hydrangea. White, panicle and arborescens types do not turn blue in acid compost. Whether an acid bag is appropriate is in the hydrangea soil buying guide. Choose open ground when the site suits the mature shrub and the colour you expect. Most hydrangeas prefer moisture-retentive soil, with shelter from strong afternoon sun and drying wind, and a spot that does not stay waterlogged. Spring or autumn is usually the easier time.

Set the depth and width of the hole

Water the hydrangea in its nursery pot about an hour before planting. Dig a hole no deeper than the rootball and about three times as wide. Lay a cane across the hole so the top of the pot compost sits level with the surrounding ground. If the hole is too deep, firm excavated soil under the rootball. Loose compost underneath can compress after watering and leave the shrub low. Backfill mainly with the excavated soil, and remove perennial weed roots. The RHS does not advise a rich organic plug or fertiliser at the base of a shrub hole. Firm gently, then water thoroughly. If the ground is too poor or chalky for the goal, change the site rather than adding more bagged medium. Container mix and bag size are in the hydrangea compost for pots guide.
SIC SIC Ericaceous 50 L

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SIC SIC Ericaceous 50 L
9.2/10about £12.49
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Water and mulch through the first season

Water enough to settle soil around the rootball, then check the root zone rather than only the surface. The RHS suggests watering newly planted hydrangeas when there has been no rain for about seven to ten days in the growing season. Sand, wind and warm weather shorten that interval. Rainwater is preferable for a blue hydrangea in acid conditions, because hard tap water raises the pH of a lime-free mix. In open ground the native soil outweighs one watering. Use mains water rather than let a new plant wilt. Mulch after watering, on moist soil, and leave a gap around the stems. Mulch does not replace watering. Feeding is not the usual first-season job. Gardeners' World notes that hydrangeas often need no extra feed, and too much nitrogen can favour leaves over flowers. A slow-release iron or six-month feed claim on a compost listing is not an instruction to add more fertiliser at planting.

What compost cannot fix after planting

Ericaceous compost cannot permanently acidify a chalk border, name a cultivar, or lift a buried crown. Every bag in this comparison conflicts between its title and another volume field, so check the packaging before you rely on a litre figure. Yellow leaves can be waterlogging, drought, transplant stress, nutrients or pH. Check moisture at root depth and the crown before you add aluminium sulphate or feed. If roots smell rotten or the site will not drain, ask an experienced gardener. Cultivar limits and rainwater are in keeping hydrangeas blue. Do not dose a colourant during establishment unless that label allows it and you know the pH.

Common questions

How deep should I plant a hydrangea?
Set the top of the nursery rootball level with the surrounding soil. The hole should be as deep as the rootball and roughly three times wider. Planting deeper than the old compost line can bury the crown, while a loose layer of compost underneath may settle and lower the shrub later.
Can I fill a hole with ericaceous compost on chalk?
You can place acid compost in a hole, but it will not reliably convert chalky ground or maintain blue flowers. Roots and drainage water soon interact with the surrounding alkaline soil. For a blue-capable hydrangea, a container of ericaceous compost provides a more controllable root zone.
When should I plant a hydrangea in the UK?
Spring and autumn are usually the easiest times because the soil is moist and temperatures are moderate. Avoid frozen, waterlogged or baked-hard ground. A container-grown shrub can be planted in summer if necessary, but you must be able to water it consistently through dry weather.
Should I add fertiliser to the planting hole?
Usually not. The RHS advises against putting fertiliser or a rich organic pocket in the base of a shrub hole, and hydrangeas often flower better without excessive feeding. Establish roots with correct depth, firm backfill and water first. Follow a specific product label later if feeding is genuinely needed.
How close can mulch sit to the stems?
Leave a clear gap of about 10 to 15 cm around the stems and crown. Mulch spread over moist soil helps conserve water, but a heap touching the plant can trap damaging moisture and obscure whether the hydrangea was planted too deeply.
When should I seek professional advice?
Ask for help if the soil is strongly chalky and you intend to acidify a whole border, if drainage keeps the root zone waterlogged, or if yellowing continues after moisture and planting depth are corrected. A soil pH test and a site diagnosis are safer than repeated undirected additions of feed or aluminium salts.

Related pages

Best ericaceous compost by job

Hydrangea soil

How to keep hydrangeas blue with soil, pH and water

Ericaceous compost for hydrangeas: what to check first

Hydrangea compost for pots: mix, size and watering

Sources

Public UK sources checked for this page in October 2026. Prices, stars and review counts are from the seven amazon.co.uk listings on file. A peat-free line, a pH and a feed period are listing claims. Title litres are not treated as the fill when the volume field disagrees. This is not a laboratory test. A 2022 Defra announcement is not a ban already in force.

  1. RHS, how to grow shrubby hydrangeas (retrieved 23 October 2026)
  2. RHS, acidifying soil (retrieved 23 October 2026)
  3. RHS, peat-free compost (retrieved 23 October 2026)
  4. Gardeners' World, ericaceous compost (retrieved 23 October 2026)
  5. Gardeners' World, how to grow hydrangeas (retrieved 23 October 2026)
  6. Defra, sale of horticultural peat to be banned (retrieved 23 October 2026)
  7. Peat Free Partnership, legislation timeline (retrieved 23 October 2026)
  8. Consumer Rights Act 2015, section 11 (retrieved 23 October 2026)