Perlite in the garden

Drainage + airflow

As mentioned earlier, perlite offers a lot of benefits to your garden.

The most important one is drainage. Perlite is a natural filtration system, allowing excess water to easily drain away while retaining a little moisture and catching nutrients that plants need to grow. This is especially true in raised beds and container gardens, but also in the ground as well.

Airflow in the soil is greatly improved in a bed amended with perlite, and that’s necessary both for your plant’s roots to breathe and for any worms, beneficial nematodes, and other good natural garden inhabitants. Because it’s a mineral glass and thus harder than the soil around it, it also helps to slow down compaction, and keeps your soil fluffy and lightweight.

Which Type of Perlite to Use

People often ask whether you should use coarse perlite as opposed to medium or fine-grade. Coarse perlite has the highest air porosity, so it offers the most drainage capability and ensures the roots of your plants can breathe well. It’s popular among people who grow orchids and succulents, and also people who do a lot of container gardening, as it provides excellent drainage, but the coarser bits don’t work their way to the surface of the soil blend as much as fine perlite does. Larger perlite is also less prone to being caught by a breeze and blown away!

The finer stuff is useful as well, but it’s used for in quality seed-starting mixes or rooting cuttings as the drainage provided encourages rapid root production. Fine perlite can also be lightly scattered across your lawn’s surface, where over time it’ll work down into the soil and improve drainage.

If you are making your own potting soil, perlite is one of the most used components in the industry for the above reasons. It’s cheap, lightweight, and easy to blend into peat or other water-retaining ingredients! But there’s other additives like diatomaceous earth and vermiculite. Why shouldn’t you use those instead?

Again, it comes back to drainage. Diatomaceous earth, or DE as it’s also referred to, is more moisture-retentive than perlite is. It’s usually available as a powder rather than a granule, so it doesn’t reduce soil compaction in the same way, and it tends to clump when wet, which doesn’t allow as good airflow. There are many other uses for diatomaceous earth in the garden including pest control, and you can use it in conjunction with your perlite, but not to replace it.

When comparing perlite vs. vermiculite, vermiculite is very moisture retentive. It’ll absorb water and nutrients and keep them in the soil, which makes it perfect for seed starting blends or for plants that prefer lots of water. In conjunction with perlite, the vermiculite will absorb water and nutrients to feed your plants, while the perlite will help drain the excess water away. So both have their own place in your garden, even in the same container or bed, but they’re not interchangeable.


PVP Horticultural Coarse Perlite

Horticultural Perlite helps plants thrive and improves soil structure, keeping it workable for years. This inorganic mineral will produce healthier plants that require less labor and watering. The water-holding ability of Perlite also increases the nutrient holding capacity when water-soluble fertilizers are used. One 4 cu. ft. bag will fill approximately 64 one-gallon nursery pots.


Seaweed mulch + compost

FLICKR: Rob n Rae Cornelius

Over the winter …

Fresh seaweed can be used as a mulch at the end of the growing season. As an organic material, seaweed will break down over time and will condition the soil ahead of the following growing season. Spread a layer of soaked and rinsed fresh seaweed 1-2 inches deep across the soil surface of garden beds. Some potato growers also have found success with putting down a layer of seaweed in their potato trench followed by a layer of compost before placing the seed potato. This method ensures that as the seaweed breaks down into the soil, the nutrients are readily available near the plant’s roots.

Seaweed can also be composted and is considered a “green” material in your compost pile or compost tumbler. You may want to chop the seaweed to 1-2 inch-long pieces to speed up the composting process to a few weeks. Layer in the seaweed in your compost pile with other natural plant materials. Seaweed is a compost accelerator because it contains a lower amount of cellulose found in other plant matter. 


Neptune’s Harvest Seaweed Fertilizer 0-0-1

Neptune’s Harvest seaweed plant food is made from seaweed (ascophyllum nodosum). It is sourced from the North Atlantic Ocean. It is an excellent addition to Neptune’s Harvest Fish Fertilizer, or other fertilizing programs.