Best Lava Rocks for Indoor Plants: 10 Bags for Drainage and Top Dressing Compared

Lava rock is porous volcanic stone, and that is the whole point. Water and air move through it, so it is popular as a grit in potting mixes and as a tidy top dressing for cacti, succulents, bonsai and houseplants.

Bags look alike, but stone size, color, bag weight and prep differ. The Midwest Hearth Black Lava Rock 1/4 in 10 lb is a 10 lb bag of 1/4 in black rock mined in the USA. The TOPZEA 12 lb Fine Black Lava Grit is a fine grit that blends into a gritty mix. The NUPICK 3 lb Mixed Lava Rock 3/8 in is a small colorful blend for decoration.

We compared 10 products by color, size, amount and notes, using only listing details. One pick, the Houseplant Smart Gravel 32 oz, is not lava rock at all and is included as a drainage alternative.

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On this page

1. Compare Lava Rocks for Indoor Plants by Color, Size and Amount
2. Detailed Reviews: Best Lava Rocks for Indoor Plants
3. Mix Lava Rock Into the Soil Rather Than Layering It at the Bottom
4. Rinse the Rock and Match the Size to the Pot
5. How to Choose Lava Rock for Houseplants
6. Which Lava Rock Should You Choose?
7. Frequently Asked Questions
8. Final Verdict

Compare Lava Rocks for Indoor Plants by Color, Size and Amount

Detailed Reviews: Best Lava Rocks for Indoor Plants

1. Black Lava Rocks for Plants, Horticultural, 1/4 in, Mined in USA, 10-lb Bag (Midwest Hearth) (Best overall black lava rock for houseplants)

• 1/4 inSize
• 10 lbBag
• BlackColor
• No dyesListed

Best for: mixing into soil, top dressing and filling pots for cacti, succulents and potted plants

Why it ranks #1: It lists a clear average size, a generous bag and no dyes or fillers.

Midwest Hearth lists 10 lb of 1/4 in black lava rock, also called scoria, mined in the USA and 100 percent natural with no dyes, additives or fillers. The listing says the rock is porous and absorbs and slowly releases excess water.

It names cacti, bonsai, succulent containers and potted plants. The listing says the rock creates a place for excess water to pool away from roots when placed at the bottom of the planter.

Skip it if you want a red color; the Midwest Hearth Red Lava Rock 1/4 in 10 lb is red.

2. Red Lava Rocks for Plants, Horticultural, 1/4 in, Mined in USA, 10-lb Bag (Midwest Hearth) (Best red lava rock for houseplants)

• 1/4 inSize
• 10 lbBag
• RedColor
• No dyesListed

Best for: a warmer color on top of pots and in mixes

Why it ranks #2: It matches the Midwest Hearth Black Lava Rock 1/4 in 10 lb in every spec except color.

Midwest Hearth lists the same 1/4 in size and 10 lb bag in a red color, mined in the USA with no dyes, additives or fillers. It names cacti, bonsai, succulent containers and potted plants.

The listing says the rock is porous and absorbs and slowly releases excess water over time.

Skip it if you want black; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is black.

3. TOPZEA 12 LB Black Lava Rocks Sand for Plants and Aquarium, 0.1-0.2 in Fine Horticultural Volcanic Rock Grit (Best fine grit for gritty mixes)

• 0.1 to 0.2 inSize
• 12 lbBag
• BlackColor
• Gritty mixUse

Best for: custom gritty potting mixes for succulents, cacti, orchids and aroids

Why it ranks #3: It is finer than the other bags, which blends into a potting mix.

TOPZEA lists a fine black lava grit about 0.1 to 0.2 in, between sand and lava rock. The listing says it blends into potting mix and makes air pockets, and names succulents, cactus, bonsai, orchids and aroids.

It suggests mixing it with soil, perlite or peat moss for a gritty mix. The listing also gives a 3 to 5 mm size, so the size figure is not exact.

Skip it if you want a larger decorative rock; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is 1/4 in.

4. NUPICK 3lb Mix Horticultural Lava Rocks for Plants, 3/8 in Gravel for Cactus (Best colorful mixed lava rock)

• 3/8 inSize
• 3 lbBag
• 6Stone types
• Rinse 2 to 3 timesPrep

Best for: colorful top dressing and vase filler

Why it ranks #4: It is the most colorful option, but the bag is small.

NUPICK lists a blend of six natural stones in 3/8 in (6 to 9 mm), non-staining and non-fading. The listing says the stones darken when wet and should be rinsed two to three times before use.

It names succulents, cacti, bonsai, aquariums and DIY projects. The listing says the rock helps drainage and aeration.

Skip it if you want a larger bag; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is 10 lb.

5. BIOMAND 18LB Lava Rocks for Plants, 3/8 in Volcanic Rock for Cactus Drainage (Best large pre-washed bag)

• 3/8 inSize
• 18 lbBag
• Pre-washedPrep
• ReusableListed

Best for: big projects and many pots that need drainage grit

Why it ranks #5: It is a large 18 lb bag that the listing says is pre-washed and reusable.

BIOMAND lists 3/8 in (5 to 10 mm) lava rocks that are pre-washed to cut dust, though some particles may remain from shipping. It names succulents, orchids, cacti and bonsai.

The listing says the rock can be used as a potting amendment, aquarium substrate or decorative topping, and that it is reusable. It does not list a color.

Skip it if you want a smaller bag; the Anothera 3 lb Black Lava Rock is 3 lb.

6. CARURBODY Black Lava Rocks for Plants, 100% Pure Volcanic Rock, No Dyes or Chemicals (Best resealable small bag)

• 3 to 6 mmSize
• 2.8 lbBag
• BlackColor
• ResealablePack

Best for: a few pots of cacti and succulents

Why it ranks #6: It is a small resealable bag with a small stone size.

CARURBODY lists a 2.8 lb pack of black lava rock, about 3 to 6 mm, with no dyes or chemicals. The listing says you can tear off the top and reseal it.

It names use as a soil additive, top dressing or bottom layer, and says the rocks must be cleaned of impurities before some uses.

Skip it if you want a bigger bag; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is 10 lb.

7. 18 Pounds Mix Horticultural Lava Rocks, 3-6 mm Lava Rocks for Plants (Planterhoma) (Best large mixed-color bag)

• 3 to 6 mmSize
• 18 lbBag
• MixedColors
• No degradeListed

Best for: terrariums, top dressing and potting mixes in bulk

Why it ranks #7: It is a large mixed-color bag that the listing says does not break down like mulch.

Planterhoma lists 18 lb of mixed horticultural lava rocks, 3 to 6 mm. The listing says they are porous for drainage and aeration, and that they do not degrade like organic mulches.

It says to wash them before use and names terrariums, vase fillers, fish tanks and fire pits.

Skip it if you want a single color; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is all black.

8. 3lb Black Lava Rock for Plant, 1/8-1/4 inch Horticultural Volcanic Rock Soil (Anothera) (Best small black top dressing)

• 1/8 to 1/4 inSize
• 3 lbBag
• BlackColor
• PorousType

Best for: bonsai, cacti and succulents as a fine top dressing

Why it ranks #8: It is a small black bag aimed at top dressing.

Anothera lists 3 lb of black lava rock at 1/8 to 1/4 in. The listing says the rock is porous and absorbs and slowly releases excess water, and names bonsai, cacti and succulents.

The listing says to place rocks at the bottom of pots, and also suggests top dressing use. It lists trace minerals but gives no numbers.

Skip it if you want a larger bag; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is 10 lb.

9. Horticultural Red Lava Rock, 8 Dry Quarts, Cactus Succulent Soil Amendment (Blue Deer Soils) (Best screened red lava rock by volume)

• 3/8 x 1/4 inScreened size
• 8 qtVolume
• RedColor
• Minimal finesListed

Best for: potting mixes and top dressing where you want few fines

Why it ranks #9: It is sold by volume and screened to a narrow size with minimal fines.

Blue Deer Soils lists 8 dry quarts, about 2 gallons, of mined red lava rock screened to mostly 3/8 down to 1/4 in with minimal fines. It is mined in the USA.

The listing says it is used to improve soil structure and drainage as a soil amendment, topping or growing medium.

Skip it if you want a weight-based bag; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is 10 lb.

10. Houseplant Smart Gravel, Reusable Drainage Rocks for Potted Plants, 32 oz (Best non-lava drainage alternative)

• 32 ozBag
• RecycledMaterial
• ReusableUse
• Non-toxicListed

Best for: a drainage layer if you prefer a non-stone, reusable gravel

Why it ranks #10: It is not lava rock, so it does not absorb water like the others.

The listing says this is a reusable drainage gravel made from recycled ocean plastics that is non-toxic and non-leaching. It names succulents, cacti, bonsai, orchids and fiddle leaf figs.

It is sold in a 32 oz bag and creates a porous layer under the soil. It is not lava rock and has no listed size.

Skip it if you want true lava rock; the Midwest Hearth Black Lava Rock 1/4 in 10 lb is natural scoria.

Mix Lava Rock Into the Soil Rather Than Layering It at the Bottom

Several listings, like the Midwest Hearth Black Lava Rock 1/4 in 10 lb and Anothera 3 lb Black Lava Rock, mention putting rock at the bottom of a pot so water can pool away from the roots. Many growers find this does not help, because water can sit in the soil just above a separate gravel layer. Mixing rock through the potting mix, as the TOPZEA 12 lb Fine Black Lava Grit listing suggests, opens up the whole soil.

A pot with a drainage hole matters more than any rock layer. For more on why a gravel base can backfire, see our guide on why you should not use polished pebbles in plant pots.

Rinse the Rock and Match the Size to the Pot

Lava rock arrives dusty. Rinse it until the water runs clear, as the NUPICK 3 lb Mixed Lava Rock 3/8 in listing advises with two to three rinses, or choose a pre-washed bag like the BIOMAND 18 lb Lava Rock 3/8 in. Dust left in a pot clogs soil.

Size matters in small pots. Fine rock like the TOPZEA 12 lb Fine Black Lava Grit and Anothera 3 lb Black Lava Rock suits small pots and top dressing, while 3/8 in rock like the NUPICK 3 lb Mixed Lava Rock 3/8 in and BIOMAND 18 lb Lava Rock 3/8 in suits larger pots and bonsai mixes. Wet rock darkens, so judge the color after watering.

How to Choose Lava Rock for Houseplants

Size

Fine grit like the TOPZEA 12 lb Fine Black Lava Grit blends into mixes. 1/4 in rock like the Midwest Hearth Black Lava Rock 1/4 in 10 lb and Midwest Hearth Red Lava Rock 1/4 in 10 lb is a good all-round size. 3/8 in rock like the BIOMAND 18 lb Lava Rock 3/8 in is chunkier.

Color

Black like the Midwest Hearth Black Lava Rock 1/4 in 10 lb looks sleek. Red like the Midwest Hearth Red Lava Rock 1/4 in 10 lb and Blue Deer Red Lava Rock 8 Quarts is warmer. Mixed bags like the NUPICK 3 lb Mixed Lava Rock 3/8 in and Planterhoma 18 lb Mixed Lava Rock give variety.

Amount

Small pots need 2 to 3 lb bags like the CARURBODY Black Lava Rock 2.8 lb. Many pots or a big repot call for 10 to 18 lb like the Midwest Hearth Black Lava Rock 1/4 in 10 lb and BIOMAND 18 lb Lava Rock 3/8 in.

Prep

Pre-washed bags like the BIOMAND 18 lb Lava Rock 3/8 in save time. Others need rinsing.

Which Lava Rock Should You Choose?

• If you want the best all-round black rock, choose the Midwest Hearth Black Lava Rock 1/4 in 10 lb, because it is a 10 lb bag of 1/4 in scoria.
• If you want red, choose the Midwest Hearth Red Lava Rock 1/4 in 10 lb, because it matches the black in size and weight.
• If you want fine grit for a mix, choose the TOPZEA 12 lb Fine Black Lava Grit, because it is 0.1 to 0.2 in.
• If you want mixed colors, choose the NUPICK 3 lb Mixed Lava Rock 3/8 in, because it blends six stones.
• If you want a big pre-washed bag, choose the BIOMAND 18 lb Lava Rock 3/8 in, because it is 18 lb and pre-washed.
• If you want a small resealable bag, choose the CARURBODY Black Lava Rock 2.8 lb, because it is 2.8 lb.
• If you want a large mixed bag, choose the Planterhoma 18 lb Mixed Lava Rock, because it is 18 lb of mixed colors.
• If you want a fine black top dressing, choose the Anothera 3 lb Black Lava Rock, because it is 1/8 to 1/4 in.
• If you want screened red rock, choose the Blue Deer Red Lava Rock 8 Quarts, because it has minimal fines.
• If you want a non-stone drainage option, choose the Houseplant Smart Gravel 32 oz, because it is reusable recycled gravel.

Frequently Asked Questions

What are the best lava rocks for indoor plants?

For most houseplants, the Midwest Hearth Black Lava Rock 1/4 in 10 lb is the best pick here, with 1/4 in black rock in a 10 lb bag and no dyes or fillers. For a fine grit, the TOPZEA 12 lb Fine Black Lava Grit mixes into soil.

Do lava rocks help drainage?

They are porous and add air spaces when mixed into potting soil. The TOPZEA 12 lb Fine Black Lava Grit listing says it creates air pockets in a mix. A drainage hole in the pot still matters most.

Should I put lava rock at the bottom of the pot?

Many listings suggest it, but many growers prefer mixing rock into the soil because a separate layer can hold water above it. Use a pot with a drainage hole.

Do I need to wash lava rock?

Yes, for most bags. The NUPICK 3 lb Mixed Lava Rock 3/8 in listing advises two to three rinses, and the BIOMAND 18 lb Lava Rock 3/8 in listing says it is pre-washed but may still have some particles.

Does lava rock change soil pH?

Some listings claim it balances pH or adds trace minerals, like the BIOMAND 18 lb Lava Rock 3/8 in and Anothera 3 lb Black Lava Rock. These are maker claims, so test your soil if pH matters.

Is lava rock safe for pets?

It is stone, but small pieces can be a choking risk for pets and young children. Keep bags and top-dressed pots out of reach where needed.

Final Verdict

The Midwest Hearth Black Lava Rock 1/4 in 10 lb is the best lava rock for indoor plants in this guide. It is a 10 lb bag of 1/4 in black scoria mined in the USA with no dyes or fillers. If you want a fine grit, the TOPZEA 12 lb Fine Black Lava Grit blends into potting mix. Before you buy, decide between mixing it into soil and using it as top dressing, and rinse it before use.

See the Midwest Hearth Black Lava Rock 1/4 in 10 lb on Amazon