Growing In Compost Without Soil: Facts On Planting In Pure Compost

planting in compost
planting in compost
(Image credit: dbsstuart)

Compost is an extremely popular and useful soil amendment that most gardeners can’t go without. Perfect for adding nutrients and breaking up heavy soil, it’s often referred to as black gold. So if it’s so good for your garden, why use soil at all? What’s to stop you from growing plants in pure compost? Keep reading to learn more about the wisdom of vegetable growing in compost without soil.

Can Plants Grow in Compost Only?

Can plants grow in compost only? Not nearly as well as you’d think. Compost is an irreplaceable soil amendment, but that’s just what it is - an amendment. Some of the essentials in compost are only good in small amounts. Too much of a good thing can lead to problems, such as ammonia toxicity and excessive salinity

And while compost is rich in some nutrients and minerals, it’s surprisingly lacking in others. Much as it might go against your gut instinct, planting in pure compost could possibly result in weak or even dead plants.

Growing Plants in Pure Compost

Growing plants in pure compost can cause problems with water retention and stability as well. When mixed with topsoil, compost works wonders with water, as it allows good drainage through heavy soil while it retains water in sandy soil. Used on its own, however, compost drains quickly and promptly dries out. 

Lighter than most soils, it can’t provide the stability necessary for strong root systems. It also compacts over time, which is especially bad for containers that won’t be nearly as full a few weeks after you plant in them. So while it may be tempting, planting in pure compost is not a good idea. 

That’s not to say you shouldn’t plant in compost at all. Just an inch or two of good compost mixed with your existing topsoil is all your plants need.

Liz Baessler
Senior Editor

The only child of a horticulturist and an English teacher, Liz Baessler was destined to become a gardening editor. She has been with Gardening Know how since 2015, and a Senior Editor since 2020. She holds a BA in English from Brandeis University and an MA in English from the University of Geneva, Switzerland. After years of gardening in containers and community garden plots, she finally has a backyard of her own, which she is systematically filling with vegetables and flowers.