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Garden lime or hydrated lime

Updated: October 2026

You have seen a bag marked builders' lime, hydrated lime, or quicklime next to a garden-centre box, and both are sold as lime. They are not the same chemical. Garden lime or hydrated lime is a safety and strength comparison: ground limestone or chalk against calcium hydroxide. None of the kept amazon.co.uk listings in this set is hydrated lime. The [garden lime comparison](/hub/fertiliser-soil-and-bark-mulch/garden-lime) is still calcium carbonate. How you spread garden lime sits on [how to apply garden lime](/hub/fertiliser-soil-and-bark-mulch/garden-lime/sub/garden-lime-how-to-apply). Products Compared did not run a laboratory trial.

You have seen a bag marked builders' lime, hydrated lime, or quicklime next to a garden-centre box, and both are sold as lime. They are not the same chemical.

Our top picks

Topline Topline garden lime 4 kg and Epsom salts 1.5 kg

Best overall

Topline Topline garden lime 4 kg and Epsom salts 1.5 kg
10.0/10about £18.95
View offer
Westland Westland lime soil conditioner, 4 kg (pack of 2)

Preis-Tipp

Westland Westland lime soil conditioner, 4 kg (pack of 2)
8.8/10about £19.98
View offer
Generic Calcium carbonate limestone chalk powder, 50 g

Alternative

Generic Calcium carbonate limestone chalk powder, 50 g
8.8/10about £3.95
View offer
On this page
  1. 1.Two chemicals, one nickname
  2. 2.Why hydrated lime is a smaller, harsher dose
  3. 3.Skin, eyes, and dust
  4. 4.What to buy instead

Two chemicals, one nickname

Garden lime, as the Royal Horticultural Society uses the name, is finely ground limestone or chalk. The active ingredient is calcium carbonate. Typical neutralising value sits around 50–55. Calcified seaweed is calcium carbonate with a typical value around 44. Hydrated lime is calcium hydroxide, the powder sold for mortars and renders. Typical neutralising value is about 70. It is quicker and stronger per kilogram, and it irritates skin and eyes. Quicklime is calcium oxide, caustic, with a typical value around 80–95. The RHS names it as not for use. BBC Gardeners' World says not to confuse garden lime with quicklime, which can injure eyes, skin, and breathing. If the safety block talks about serious eye damage and wet material that can burn, that is calcium hydroxide. A liming-material definition on legislation.gov.uk does not make hydroxide a gentle garden product.

Why hydrated lime is a smaller, harsher dose

At about 70 against about 50–55, hydrated lime cancels more acidity per kilogram than ground limestone. The RHS says you need much less hydrated lime than calcium carbonate. Much less stays qualitative on this page. There is no converted kilogram table here, because a homemade conversion is how gardeners over-apply a builders' bag. The same fineness that makes hydrated lime quick is what makes it harsh. Pelleted garden lime is still calcium carbonate; pelleting does not raise the value, and it does not turn the pellets into hydroxide. If you came from best garden lime looking for a faster pellet, that is still not this chemical. A US extension page tells one asker not to put hydrated lime on a lawn or vegetable garden at all. The RHS is milder: a much smaller amount, with gloves and goggles. This page follows the RHS and still leads with irritation.
Topline Topline garden lime 4 kg and Epsom salts 1.5 kg

Testsieger

Topline Topline garden lime 4 kg and Epsom salts 1.5 kg
10.0/10about £18.95
View offer

Skin, eyes, and dust

Traditional Lime's health sheet treats hydrated lime as irritating to eyes and skin. Wet material can burn. The stated first aid is to irrigate eyes for at least 20 minutes and seek medical attention, and to wash skin immediately. CEMEX UK classifies calcium dihydroxide as a skin irritant with serious eye damage. Those are building-product sheets, not a sowing rate. If dust has already irritated eyes or skin, get medical help. Garden-centre calcium carbonate still wants gloves and washed skin on a Westland label. That is ordinary handling for a dusty carbonate, not the same warning as a hydroxide burn. Do not slake quicklime as a shortcut. Gypsum contains calcium without carbonate and does not correct acidity. The buying checks for a carbonate box sit on the garden lime buying guide.

What to buy instead

Buy ground limestone or chalk unless you already understand the smaller dose and the hazard. That is the RHS recommended material, and it is the material on these amazon.co.uk pages. None of the kept listings is labelled hydrated lime. If the job is a tested acid bed, you want kilograms of calcium carbonate you can weigh, not a builders' bag and not a 50 g jar. If the job is vegetables, the crop rules on garden lime for vegetables still apply. If you already own hydrated lime for mortar, keep it for mortar. Substituting it one-for-one on a 4 m² bed is the error this page exists to stop.

Common questions

Is hydrated lime the same as garden lime?
No. Garden lime is ground limestone or chalk, calcium carbonate, typical neutralising value about 50–55. Hydrated lime is calcium hydroxide, typical value about 70, sold for builders. They share a nickname and not a handling profile.
Can I use builders' lime on the soil?
The RHS allows hydrated lime in a much smaller amount, with gloves and goggles. A US extension page tells gardeners not to apply it at all. This page follows the RHS, leads with irritation, and does not give a converted rate. For a home bed, calcium carbonate remains the recommended material.
Why does hydrated lime need a smaller amount?
Its typical neutralising value is about 70 against about 50–55 for ground limestone, so a kilogram cancels more acidity. The RHS says "much less". This page does not print a homemade conversion table, because that is how people over-apply a builders' bag.
What is quicklime, and is that safe in the garden?
Quicklime is calcium oxide, typical neutralising value about 80–95. The RHS names it as caustic and not for use. BBC Gardeners' World warns that it can injure eyes, skin, and breathing. Do not slake it as a garden shortcut.
What should I wear if a bag is calcium hydroxide?
Gloves and goggles, on the RHS account. Building sheets add that wet material can burn and that eye contact needs irrigation and medical attention. If dust has already irritated eyes or skin, get medical help. Do not treat Westland's carbonate gloves line as the same warning.
Is dolomite lime the same argument?
No. Dolomite is magnesian limestone, still a carbonate. Buy it only if a test shows magnesium is low. Extra magnesium on a high-magnesium clay is not wanted. It is not hydrated lime and it is not a reason to use builders' lime.
Which amazon.co.uk listing in this comparison is hydrated lime?
None. Every kept ASIN is calcium carbonate in some garden, pellet, algae, powder, or bundle form, or a conflicting listing. There is no hydrated-lime pick in this set.

Related pages

Garden lime comparison

How to apply garden lime

Best garden lime

Garden lime buying guide

Garden lime for vegetables

Sources

Public UK and maker sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the figures stored with the eight amazon.co.uk listings, not a fresh shop check. A star line is not a measured pH rise. Hydrated lime is not one of these listings.

  1. RHS, lime and liming (retrieved October 2026)
  2. RHS, soil pH (retrieved October 2026)
  3. RHS, club root (retrieved October 2026)
  4. RHS, blossom end rot (retrieved October 2026)
  5. RHS, potato scabs (retrieved October 2026)
  6. AHDB, soil pH and liming recommendations (retrieved October 2026)
  7. Westland garden lime (retrieved October 2026)
  8. legislation.gov.uk, liming material (retrieved October 2026)