Popular Products
Pumice Stone Calculator for Pots, Garden Beds and Nursery Mix
This pumice stone calculator tells you how much pumice to mix into your soil, based on what you are growing and how much soil you are working with. Choose pots, garden beds, trees and shrubs, or nursery mix, enter your numbers, and you get the amount in kilograms and litres, the number of bags to buy, and the estimated cost. It takes a few seconds and saves you from guessing.
What Is Pumice Stone for Plants?
Pumice stone is a light, porous volcanic rock. For gardening, it is crushed and graded into small grains, often called horticultural pumice, and mixed into potting soil, garden soil and nursery media. The grains are full of tiny air pockets, so they open up space between soil particles. Water drains faster, air reaches the roots, and the soil is less likely to turn soggy or compact.
Unlike peat, cocopeat or compost, pumice does not break down over time. The structure it gives your soil lasts for years, which is why growers use it for container plants, succulents, cactus, bonsai, orchids, aroids such as monstera, and seed starting and propagation mixes. The pores also hold a little water, so roots get moisture between waterings.
One thing to remember: pumice is not a fertilizer. It improves soil structure, aeration and drainage, but it adds almost no nutrients. For feeding, mix it with compost, vermicompost or neem cake.
Benefits of Pumice Stone in Soil
- Better drainage: excess water leaves the pot or bed faster, which lowers the risk of overwatering and root rot.
- More air at the roots: the porous structure improves soil aeration and root growth.
- Loosens heavy clay: pumice opens up compacted soil so water and roots can move through.
- Long lasting: it does not decompose, so you can reuse it when repotting.
- Stays mixed: it is heavier than perlite, so it tends to stay spread through the soil instead of floating to the top.
- Light moisture buffer: the pores hold a small amount of water that roots can use between waterings.
How to Use the Pumice Stone Calculator
- Pick what you are using pumice for: pots, garden beds, trees and shrubs, or nursery mix.
- Enter your details, such as the number of pots and pot size, the bed area and mix-in depth, the number of plants, or the total volume of mix you want to make.
- Choose the pumice share: conservative, standard or heavy.
- Check the result. You will see the pumice needed in kg and litres, bags of 10 kg and 25 kg, the recommended grain size, the cost, and how the mix splits between pumice and soil with compost.
- Copy the summary, print it, save it as an image, or send it on WhatsApp.
You can also change the pumice density, the extra amount for settling, and the price per kg so the result matches what you pay. For more tools, see our gardening calculators.
How Much Pumice to Add to Soil
The right amount depends on the plant. Pumice is measured as a share of the total soil volume, not the weight. These are common starting points for a pumice soil mix ratio:
| Use | Conservative | Standard | Heavy | Why |
|---|---|---|---|---|
| Succulents and cactus | 40% | 50% | 60% | Fast drainage for dry-loving roots |
| Indoor and foliage plants | 20% | 30% | 40% | Keeps roots aerated indoors |
| Flowering and ornamental plants | 15% | 25% | 30% | Balanced moisture and air |
| Vegetables and herbs | 10% | 20% | 25% | Needs steady moisture |
| Roses | 10% | 15% | 20% | Likes moisture with good drainage |
| Garden beds, normal soil | 10% | 15% | 20% | Mixed into the top layer |
| Garden beds, heavy clay | 20% | 25% | 30% | Opens up compacted soil |
| Trees and shrubs (backfill soil) | 10% | 15% | 25% | Mixed evenly into the planting hole |
| Seed starting mix | 20% | 30% | 40% | Light, airy mix |
| Cuttings and propagation | 40% | 50% | 70% | Helps stop rot at the base of cuttings |
| General potting mix (bulk) | 20% | 30% | 40% | Good all-round blend |
These figures are general guidelines, not fixed rules. Your climate, watering habits and the soil you start with all matter. If you water often or live in a humid area, lean toward the heavier end for drainage. If the weather is hot and dry, a lower share usually suits most plants, except succulents and cactus.
Pumice for Succulents and Cactus
Succulents store water in their leaves and stems, and their roots rot quickly in wet soil. A succulent soil mix with around half pumice drains fast and dries out evenly. Our Pumice Stone 7-14mm Coarse suits cactus, succulent and bonsai mixes, and the Fine Pumice Stone 3-6mm works well for small pots and seedlings.
Pumice for Vegetables and Herbs
Vegetables and herbs need steady moisture, so they do better with less pumice, usually 10 to 25 percent. This gives the soil better air and drainage without drying out too quickly.
Pumice for Indoor Plants, Monstera and Aroids
Indoor plants, monstera and other aroids like a loose, airy mix. About 30 to 40 percent pumice, blended with cocopeat or potting soil and a little vermicompost, keeps the roots aerated. For big planters and chunky aroid mixes, the Pumice Stone 16-22mm grade works well.
Pumice for Heavy Clay Soil
Clay soil holds water and can turn hard and compact. Mixing pumice evenly into the top layer opens the soil and helps water move through. The calculator uses a mix-in depth, set to 6 inches by default, and you can change it.
Pumice Needed Per Pot
This table shows the pumice for one pot at the standard share, with a density of 0.7 kg per litre. The calculator gives exact figures for any pot size and plant type.
| Plant type (standard share) | 6 inch pot (1.5 L soil) | 8 inch pot (3 L soil) | 10 inch pot (5 L soil) | 12 inch pot (8 L soil) |
|---|---|---|---|---|
| Succulents and cactus (50%) | 0.75 L (525 g) | 1.5 L (1,050 g) | 2.5 L (1,750 g) | 4 L (2,800 g) |
| Indoor and foliage (30%) | 0.45 L (315 g) | 0.9 L (630 g) | 1.5 L (1,050 g) | 2.4 L (1,680 g) |
| Flowering plants (25%) | 0.38 L (263 g) | 0.75 L (525 g) | 1.25 L (875 g) | 2 L (1,400 g) |
| Vegetables and herbs (20%) | 0.3 L (210 g) | 0.6 L (420 g) | 1 L (700 g) | 1.6 L (1,120 g) |
| Roses (15%) | 0.23 L (158 g) | 0.45 L (315 g) | 0.75 L (525 g) | 1.2 L (840 g) |
Pumice for Garden Beds and Raised Beds
For beds, the amount depends on the area and how deep you mix it in. The table below is for 100 square feet of bed, mixed in to 6 inches deep (about 1,416 litres of soil), with a density of 0.7 kg per litre.
| Soil type | Share | Pumice volume | Pumice weight |
|---|---|---|---|
| Normal soil, conservative | 10% | 142 L | 99 kg |
| Normal soil, standard | 15% | 212 L | 149 kg |
| Normal soil, heavy | 20% | 283 L | 198 kg |
| Heavy clay, conservative | 20% | 283 L | 198 kg |
| Heavy clay, standard | 25% | 354 L | 248 kg |
| Heavy clay, heavy | 30% | 425 L | 297 kg |
Figures are before the small extra for settling. A shallower mix-in depth needs proportionally less. Use the calculator for your exact bed size.
Pumice for Trees and Shrubs
When planting fruit trees, shrubs and ornamentals, mix pumice evenly through the backfill soil that goes back into the planting hole. Avoid a pocket of pure pumice, because it can dry out the roots.
| Planting hole size | Soil volume | Conservative (10%) | Standard (15%) | Heavy (25%) |
|---|---|---|---|---|
| Small, 1 ft cube | 28 L | 2.8 L (2 kg) | 4.2 L (2.9 kg) | 7 L (4.9 kg) |
| Medium, 1.5 ft cube | 96 L | 9.6 L (6.7 kg) | 14.4 L (10.1 kg) | 24 L (16.8 kg) |
| Large, 2 ft cube | 227 L | 22.7 L (15.9 kg) | 34 L (23.8 kg) | 56.8 L (39.7 kg) |
Which Pumice Size Is Best?
The grain size does not change how much pumice you need, but it changes how well the mix suits your plants. Use smaller grains for small pots and seedlings, and larger grains for bigger containers, beds and trees. You can also blend two grades in one mix.
| Grade | Size | Best for | Typical use |
|---|---|---|---|
| Fine Pumice Stone 3-6mm | 3 to 6 mm | Seedlings, propagation, cuttings, succulents | Seed starting mix, small pots, cuttings |
| Pumice Stone 7-14mm Coarse | 7 to 14 mm | Bonsai, cactus, succulents, monstera | Most pots, garden beds, general potting mix |
| Pumice Stone 16-22mm | 16 to 22 mm | Big pots, planters, orchids, aroids | Large containers, heavy clay, tree planting holes |
Pumice Soil Mix Recipes
Here are simple recipes by volume. Mix everything evenly, water once to settle the mix, then top up.
| Mix | Pumice | Other ingredients |
|---|---|---|
| Succulent and cactus mix | 50% (7-14mm or 3-6mm) | 40% potting soil, 10% vermicompost |
| Indoor, monstera and aroid mix | 30% (7-14mm) | 40% cocopeat, 20% potting soil, 10% vermicompost |
| Orchid and chunky aroid mix | 30 to 40% (16-22mm) | Orchid bark and a little cocopeat |
| Vegetable and herb mix | 20% (3-6mm or 7-14mm) | 60% garden soil, 20% vermicompost |
| Rose and flowering plant mix | 15 to 25% (7-14mm) | 55 to 65% garden soil, 20% vermicompost |
| Seed starting mix | 30% (3-6mm) | 60% cocopeat, 10% vermicompost |
| Cutting and propagation mix | 50% (3-6mm) | 50% cocopeat |
Pumice Stone Weight, Density and Bag Size
Recipes are usually given by volume, but pumice is sold by weight. To convert between them, you need the density. Dry pumice is generally about 0.5 to 0.9 kg per litre, and the calculator uses 0.7 kg per litre as its default. Wet pumice is heavier, and different grades vary, so if you know the weight per litre of your pumice, enter it in the density field.
| Volume | At 0.5 kg per litre | At 0.7 kg per litre | At 0.9 kg per litre |
|---|---|---|---|
| 1 litre | 0.5 kg | 0.7 kg | 0.9 kg |
| 5 litres | 2.5 kg | 3.5 kg | 4.5 kg |
| 10 litres | 5 kg | 7 kg | 9 kg |
| 25 litres | 12.5 kg | 17.5 kg | 22.5 kg |
| 50 litres | 25 kg | 35 kg | 45 kg |
The calculation works in three steps:
- Pumice volume = total mix volume × pumice share × (1 + extra for settling)
- Pumice weight = pumice volume in litres × density
- Bags = pumice weight divided by bag size, rounded up
Pumice vs Perlite vs Vermiculite vs Cocopeat
These soil amendments are often used together, but each does a different job.
| Material | Main job | Weight | Water holding | Lasts in soil |
|---|---|---|---|---|
| Pumice | Drainage and aeration | Light but heavier than perlite | Low to moderate | Years, does not decompose |
| Perlite | Drainage and aeration | Very light, can float to the top | Low | Long, but can crumble |
| Vermiculite | Water and nutrient holding | Light | High | Softens and compacts over time |
| Cocopeat | Moisture holding base | Light | High | Breaks down slowly |
Pumice and perlite do a similar job. Pumice is heavier and holds its shape longer, while perlite is lighter. Combining pumice with cocopeat gives you a mix that holds some moisture but still drains well.
Common Problems and Fixes
| Problem | Likely cause | What to do |
|---|---|---|
| Soil dries out too fast | Pumice share is too high for the plant | Use the conservative level next time, or add more cocopeat or compost |
| Soil stays wet for days | Not enough drainage | Raise the pumice share and check that the pot has drainage holes |
| Pumice floats to the top | Heavy watering on a light mix | Mix evenly and water gently, or use a coarser grade |
| Seedlings dry out | Grains too large for small seeds | Use the fine 3-6mm grade |
| Plants look hungry | Pumice does not feed plants | Add vermicompost, compost or neem cake |
| Clay bed still compacts | Mix is too shallow or too thin | Mix deeper, use the heavy clay share, and add organic matter |
Tips for Mixing Pumice into Soil
- Mix it evenly. Spread the pumice through the whole soil volume instead of layering it at the bottom or making a pocket in the hole.
- Add organic matter. Combine pumice with compost, vermicompost or neem cake so the plants still get nutrients.
- Settle the mix. Water once after filling the pot or bed, then top it up, since the soil will drop a little. The calculator adds a small extra for this.
- Start with the standard level. If plants dry out too fast, reduce the share next time. If the soil stays wet, increase it.
- Match the grain size to the job. Follow the recommended size shown in the calculator result.
Who Is This Pumice Calculator For?
- Home gardeners filling pots and balcony containers
- Nurseries preparing potting mix in bulk
- Farmers and orchard owners planting trees and shrubs
- Landscapers improving heavy clay in garden beds
- Succulent, cactus, bonsai, orchid and aroid growers who want a fast-draining mix
Buy Pumice Stone in Pakistan
Organic Baghbani sells three grades of pumice stone (پیومس اسٹون) for plants. Pick the grade from the size table above, use the calculator to find the quantity, and order online. You can check delivery on our delivery overview page, or visit us from the store locations page.
| Product | Best for | Link |
|---|---|---|
| Fine Pumice Stone 3-6mm | Seedlings, propagation and succulents | Buy fine pumice stone |
| Pumice Stone 7-14mm Coarse | Bonsai, cactus, succulents and monstera | Buy coarse pumice stone |
| Pumice Stone 16-22mm | Big pots, planters, orchids and aroids | Buy large pumice stone |
Browse the full Potting Mix and Growing Media category, or message us on WhatsApp with your calculated quantity and we will help you pick the right grade.
Frequently Asked Questions About Pumice Stone
Can I use pumice alone as a growing medium?
Pumice can be used alone for propagation or for some succulents, but most plants do better when it is mixed with soil and compost. Pumice holds little water and almost no nutrients, so plants grown only in pumice need regular watering and feeding.
How much pumice do I need for a 10 inch pot?
A 10 inch pot holds about 5 litres of soil. At the standard share for flowering plants, which is 25 percent, that comes to roughly 1.25 litres of pumice, which weighs close to 0.9 kg at 0.7 kg per litre. The calculator shows the exact figure for your plant type.
How much pumice do I need per 100 square feet of garden bed?
For normal soil mixed in to 6 inches deep at the standard 15 percent share, you need about 212 litres, or roughly 149 kg at 0.7 kg per litre. Heavy clay at 25 percent needs about 354 litres, or roughly 248 kg.
What size of pumice is best for succulents?
For small pots, the fine 3-6mm grade works well. For most succulent, cactus and bonsai mixes, the 7-14mm coarse grade is a popular choice because it drains quickly and keeps the mix open.
Does pumice change soil pH?
Pumice is generally close to neutral and does not change soil pH in a big way. If pH is important for your crop, test your soil and your pumice supply, because it can vary by source.
Will pumice float to the top of the pot?
Pumice is light, so some pieces can rise a little when you water heavily. It is heavier than perlite, so it tends to stay mixed in better. Mixing it evenly and watering gently reduces this.
How long does pumice last in soil?
Pumice does not decompose, so it keeps its structure for years. You can reuse it when repotting by sifting it out of old soil and rinsing it.
Is pumice better than perlite?
They do a similar job. Pumice is heavier and holds its shape longer, while perlite is lighter and crumbles more easily. The best choice depends on your plants, your budget and what is available near you.
Final Thoughts
A good soil mix needs both structure and nutrients, and pumice takes care of the structure. Use this pumice stone calculator to work out the right amount for your pots, beds, trees or nursery, then buy exactly what you need. If you are unsure, start with the standard level and adjust after watching how your plants respond.
