Is LECA A Good Substitute For Soil? Plant Experts Weigh In

LECA, or lightweight expanded clay aggregate, is made of little pieces of clay that have been cooked at high heat to the point of bursting.

The resulting tiny, Cocoa Puff–esque clay pebbles filled with air bubbles are often used in industrial hydroponic gardens, ones that swap soil for another growing medium.

If you're a rooftop grower who needs to keep things light, LECA is a great alternative to heavy soil. Indoor farmers who grow crops year-round also use LECA because it can lead to better yields in climate-controlled conditions.

LECA rocks allow for more air circulation than compact layers of soil. As such, they can help prevent some of the common side effects of overwatering, like pests and root rot. Since these rocks also absorb water and then slowly release it, people claim it allows them to water their plants less frequently.

But there are some downsides to swapping soil for sterile clay. You can think of LECA as a totally blank slate: It doesn't have the living organisms that could attract mold or pests, but it doesn't have any of the beneficial nutrients you'll find in soil either. As such, those who use LECA need to constantly fertilize it to ensure their plants have enough nutrients like nitrogen, phosphorous, and potassium.

Another reason someone might use LECA or another type of pebble is if they want to improve their soil's drainage. The idea is that placing them at the bottom of a pot (underneath the soil) can help store any excess water and keep it from drowning a plant's roots.

This technique gets mixed reviews: While some people claim it can help prevent overwatering, others say that it can actually do more harm than good, due to something called the perched water table.

"Basically, there's a difference in medium between the rocks and the soil, so all the water will saturate at the bottom of the soil instead of settling where the rocks are," explains plant care expert and chemistry teacher Paul Thompson, M.A. "Now, you've moved that level of saturation up higher, to where the roots are." This can cause water to choke the roots and lead to rot, which is hard to bounce back from.

There is, however, one thing that can basically ensure you won't overwater your plants, whether you're using LECA or not: a drainage hole.

When keeping plants indoors, you'll want to recreate the outdoor environment they've adapted to. And, as Thompson reminds us, "in nature, plants can easily get rid of excess water because they have the whole ground. But when you're talking about a tiny little volume, it's so important to have that drainage so extra water can drain out."

Marie Viljoen, the urban gardener, author, and chef behind 66 Square Feet (Plus), agrees, cautioning, "Do not go for a pot without drainage holes. If it doesn't [have any], drill a hole in it... That's the No. 1 thing a container needs."

Drainage holes also provide a visual cue that you've given your plant enough water. Once you see it trickling from the bottom of the pot, it's a sign your soil is moist enough. Without one, it's impossible to know if your plant is still thirsty—or on the verge of drowning.

LECA can be used as a soil amendment or replacement, to reduce the risk of accidentally drowning a plant. While these clay pebbles do help deliver more oxygen to a plant's roots, they can easily turn sour when used incorrectly.