Gardening: the Truth about Cardboard

Jeff Gillman, the author ofThe Truth About Gardening Remedies, has been debunking garden myths for years. We asked him about cardboard gardening, and here's what he had to say.

Are there concerns about using cardboard in the garden?
The biggest problem with cardboard is that it will break down pretty rapidly. Directly in the compost pile, it will only last a couple of weeks. In the garden, it breaks down a little more slowly. So keep in mind that it probably won’t last longer than a growing season.

Do you have to worry about formaldehyde in the glue used with cardboard?
You really don't. The formaldehyde is at such a low level that it really shouldn't do anything. Furthermore, as time goes on the amount of formaldehyde will decrease.

Is it OK to grow veggies in cardboard?
Yes, though do be aware of what the cardboard held before you use it. If it was used for shipping industrial chemicals, for example, it might be best to avoid it. But in general, cardboard should be fine.

Is it OK to leave cardboard in the garden to break down on its own?
Yes. Cardboard is really nothing more than ground and processed trees, and so it returns to the ground the same as any wood mulch would.

If you're looking to start using cardboard in your own garden, keep these tips in mind to stay on the right track:

1. Before:Inspect the cardboard and make sure it hasn't been contaminated with anything that might have been shipped in it. Also, if you're using it as a container, reinforce any weak areas.

2. During: If you’re growing plants in the cardboard, water directly in the center to avoid drenching and weakening the sides. If using it as a mulch or weed barrier, keep it watered to aid in breakdown.

3. After: Leave the cardboard in the garden, letting it break down naturally. Or if you’d like, move it to your compost bin at the end of the season.