Can I Reuse Old Potting Soil?

Gayla Trail shares what she's learned about reusing potting soil.
Lavender in Silver Containers

Lavender in Silver Containers

Photo by: DK - Small Garden © 2004 Dorling Kindersley Limited

DK - Small Garden , 2004 Dorling Kindersley Limited

Q: Can I reuse old potting soil?

ANSWER:

When I started out as a container gardener I could not find literature that addressed this issue, the implication being that one would start out fresh each spring. This is fine when we’re talking about a pair of containers flanking the front door, but when containers ARE your garden, and the soil has to be carried up three flights of stairs without an elevator… I threw caution to the wind that second year and have never looked back. Allow me to share what I learned along the way.

Potted soil is not technically soil at all. It is a close approximation of the real deal comprised of lightweight fillers to aid drainage, and organic matter that provides nutrition and water retention. This substitution is necessary as soil from the garden will become compacted in pots and rot your plants’ roots. Nutrients and organic matter leach out of a pot much faster than they do in the ground or a raised bed. By year’s end what’s left in the pot is primarily filler with very little nutrition if any at all.

In the springtime, just before planting:

  • Replenish depleted potted soil with organic matter such as compost or manure. Add no more than 25% organic matter to 75% old soil. Compost is dense, so using too much can lead to that compaction you are trying to avoid. Vermicompost, aka worm poop, is a lightweight, nutritionally balanced additive (approx. equal (N) nitrogen, (P) phosphorous, and (K) potassium) that I prefer for containers. Start a worm bin and make your own!
  • Add more fillers such as coir (coconut husk fiber), grit, or perlite if the mix feels too heavy.
  • Slow-release fertilizers are also good additives that won’t weigh down the mix. I always add kelp meal by the handful to help plants deal with the stresses of container life as well as crushed eggshells, which add both calcium and act as grit, and fishmeal for nitrogen and healthy leaf growth.
  • Diseases can carry over so do use fresh soil with disease-prone crops like tomatoes, or in pots where disease was previously a problem. To avoid spreading disease I practice crop rotation between pots, using the old mix for tough herbs that are better suited to poor soil.

Garden authority Gayla Trail is the creator of YouGrowGirl.com.

Keep Reading

Next Up

Tips for Watering Lawns and Gardens

Without adequate water, plants will suffer and eventually die. Supplies can run short as rapidly growing plants draw up moisture from the soil. It's important to know what to water and how.

How to Fertilize Your Lawn and Garden

Learn how adding fertilizer can be beneficial, especially for fruits, veggies and container plants. Fertilizers can also help kick-start growth after planting and reinvigorate plants that have been pruned hard.

Watering Lawns and Gardens

Thorough, careful watering encourages deep, drought-resistant roots in your lawn and garden. Follow the steps below to ensure best results.

Garden Plants and Flowers

Learn how to discover which plants underscore and help define a specific garden design style.

How to Plant in Gardening Containers

To ensure that plants in gardening containers grow and perform as well as possible, you need to plant them properly.

Family Planting: Tropical Garden

A tropical border is one of the most exciting plantings, filled with bold, colorful plants and reminiscent of a child’s fantasy jungle.