How often should I replace container soil?
Written by
Liu Xiaohui
Reviewed by
Prof. Martin Thorne, Ph.D.Healthy herbs require replacement of the container soil, or nutrients become depleted, and salt builds up. Annuals, such as basil, use up their soil's nutrients in one season. At the same time, Mediterranean perennials require a fresh mix every few years. Old soil becomes so compacted that roots cannot grow, and water passes through only slowly.
Annual Herbs
- Basil, cilantro, dill
- Replace every 8-12 months
- Nutrients depleted after single season
- Discard soil to prevent disease carryover
Perennial Mediterranean
- Rosemary, thyme, sage
- Refresh every 2-3 years
- Top-dress annually with compost
- Full replacement prevents root binding
Moisture-Loving Perennials
- Mint, lemon balm, chives
- Replace soil annually
- Organic matter breaks down faster
- Prevents fungal diseases in damp soil
Refreshing soil. For perennials, remove the top three inches and replace them with a compost-enriched mixture. Be careful to root-prune the circling roots when you repot at a lower level. All annuals should be shaken from their soil and entirely replenished; the pots should be sterilized with a solution of vinegar in water. Always water at the roots when repotting to help them settle into the soil.
Extend your soil's life, with just a touch of proper maintenance...top-dress with compost every spring for your perennials, flush your containers monthly by watering till the drainage runs clear, use organic fertilizers to avoid salt build-up. You can add an incredible six months to your replacement time.
Repurpose old soil sustainably - blend it into your vegetable beds (aided by sterlisation) if you've been growing in containers. You can mix it with rotten compost and use it for your ornamental plants, or mix it here and there to make a potting mix for vegetables. Never, ever, use the soil from your pots to plant vegetables in. Herbs too.
Read the full article: Best Soil for Herbs: Ultimate Growing Guide
