Perlite is often added to soil by gardeners and horticulturists to make it drain and breathe better. But it can be hard to figure out how much perlite to use for each gallon of soil. Use too little, and you won’t see the desired effects. You could end up with a mix that drains too quickly because it has too many holes.
This full guide will tell you everything you need to know to find the right amount of perlite for each gallon of soil.
What is Perlite and Why is it Used?
Perlite is a volcanic glass that has been superheated to form a lightweight, porous material. It has several key properties that make it beneficial as a soil amendment:
- Improves aeration by creating air pockets in soil
- Allows excess water to drain freely, preventing soggy soil
- Lightweight and easy to incorporate into mixes
- Chemically inert so it doesn’t alter soil chemistry
By adding perlite, gardeners can improve drainage and oxygen flow to plant roots This is especially helpful for container gardening where soil compaction is common Perlite is suitable for all types of plants but is especially useful for those prone to overwatering.
General Rule of Thumb for Perlite Usage
It’s not possible to find the perfect ratio, but a good general rule is to use perlite at a percentage of 2010–50% of your total soil volume. Most gardeners find that 2020–30% perlite%20per%20volume%20is%20suitable%20for%20a%20wide%20variety%20of%20plants.
To calculate how much perlite per gallon of soil:
- 10% of 1 gallon is 0.1 gallon or 1.6 cups
- 20% of 1 gallon is 0.2 gallon or 3.2 cups
- 30% of 1 gallon is 0.3 gallon or 4.8 cups
So for example, for a 5 gallon pot you would use 1-1.5 gallons of perlite, or about 16-24 cups.
Factors That Influence Perlite Use
The 20% to 30% per gallon range is good for many plants, but the exact amount needed depends on a number of things, such as:
Type of Plant
- Succulents/cacti need excellent drainage so use 40-50% perlite.
- Vegetables do well with 20-30% perlite.
- Moisture loving plants only need 10-20% perlite.
Type of Soil
- Heavy clay soil benefits from more perlite, 30-40%, to improve drainage.
- Sandy soil may only need 10-20% since it already drains well.
- Most potting mixes are fine with 20-30% perlite.
Environmental Conditions
- In humid climates, increase perlite to promote drainage.
- In very dry climates, reduce perlite to retain moisture.
Type of Container
- Add more perlite if using a container with few drainage holes.
- Use less if planting in a highly porous container.
How to Properly Mix Perlite into Soil
To incorporate perlite correctly:
- Start with dry soil for easier mixing
- Gradually add perlite a little at a time
- Gently combine, avoiding compaction
- Fill containers lightly, don’t pack down
- Adjust ratio based on how plants respond
Alternatives to Perlite
While perlite is a go-to amendment, other options include:
- Vermiculite – improves moisture retention
- Coir – enhances aeration and drainage
- Horticultural sand – provides excellent drainage
The ideal amount of perlite varies based on your specific needs, but 20-30% perlite per volume is a suitable starting point for most plants. Adjust this ratio based on your soil, plants, climate and containers. With a properly amended soil mix, perlite can vastly improve drainage and aeration for thriving, healthy plants.
Vegetable and Flower Gardens
- For gardens or new lawns, till the ground to a depth of 150–300 mm (6–12 inches) by hand or with a rototiller.
- A thick layer of a mix of half perlite and half peat moss or compost should be put down, and it should be mixed into the soil. (If the soil has a lot of organic matter already, you may not need to add the peat or compost.) ).
- If the garden is very big, the person gardening at home may only prepare the rows or areas where plants will go. If the process is kept up for two to three years, the whole garden will be in good shape.
- In dry parts of the Middle East, putting a layer of perlite under new sod has been shown to cut down on irrigation by up to half.
- Applying perlite to lawns that don’t get enough air flow or are prone to drought can make them better. Plugs should be used to open up the lawn, and perlite should be raked into the holes or worked in with irrigation water. It might take as much as 50 L/m2 (1 gallon/sq ft) to get the job done. Apply a few smaller amounts over several seasons to get the concentration you want.
Perlite is a valuable component of growing media used for container growing and patio planters. Planters with a mix of perlite and soil are light, even when they’re full of water. This makes them easier to move or rearrange to protect plants from bad weather.
- One third should be perlite, one third should be peat moss, and one third should be composted wood products like bark or shavings.
- Although perlite doesn’t hold as much water as other materials, it helps garden planters and raised beds keep water longer and supply just the right amount of water for plant growth.
Using Perlite with Different Soil Types
No matter what kind of soil you have, adding horticultural grade perlite will make it better right away and have long-lasting benefits. Fine grade perlite can be used to add more moisture holding capacity, and coarser grades will increase aeration. No matter which size you have on-hand, horticultural grade perlite improves both the moisture-holding capacity of the soil, as well as introducing all-important pore spaces for air and water to penetrate the root zone. Depending on the size, horticultural grade perlite holds up to 8x its weight in water, while increasing the level of oxygen available to plant roots and promoting healthy biological activity. Because perlite is completely natural and stable, it continues to provide these benefits year after year.
5 quick tips Perlite
FAQ
What is the ratio of perlite to soil?
When planting shrubs, trees, and ornamentals, fill the hole with perlite to protect the roots of the plants and hold more water. Add a mixture of 1/3 soil, 1/3 perlite, and 1/3 peat moss or compost to the hole.
Can you add too much perlite to soil?
Even though perlite won’t hurt the soil, it will slowly rise to the top because it’s so much lighter than mineral soil particles. Heavy water saturation and critter soil-mixing action will tend to gradually bring it upwards.
How much perlite to mix with potting mix?
As perlite is porous, it also absorbs water, but its main role is to improve drainage and make the mix lighter. Mix it with bagged potting mix about 50:50 (equal parts perlite and sieved potting mix or compost by volume) to make a mix for getting plants to grow.
Is it good to mix perlite with soil?
By improving drainage, perlite prevents water from stagnating around the roots, which is harmful. And by retaining moisture, it keeps the soil from drying out too quickly, ensuring plants have access to water as they need it. This dual action makes perlite an excellent soil amendment for promoting healthy plant growth.