Why is proper drainage critical for herbs?
Written by
Liu Xiaohui
Reviewed by
Prof. Martin Thorne, Ph.D.Drainage is likewise essential to health, for the roots of an herb, like those of a man, revolt against being submerged in water, which excludes air. Mediterranean plants, such as rosemary, do not require boggy soil. Left in water for many days, and they are dead. Even mint, fond as it is of water, grows yellow and thin if its roots do not get plenty of air.
Root Suffocation
- Water fills air pockets in saturated soil
- Oxygen deprivation occurs within 12 hours
- Roots turn brown and mushy rapidly
- Plant collapse follows in 3-5 days
Disease Proliferation
- Fungi like Pythium thrive in wet conditions
- Root rot spreads through entire root systems
- Pathogens multiply 10x faster without drainage
- Infection becomes irreversible once established
Nutrient Lockout
- Excess water dissolves essential nutrients
- Iron and nitrogen wash away before absorption
- pH imbalance prevents mineral uptake
- Deficiency symptoms appear despite fertilization
Drainage, done correctly. Use materials wisely: mix 30% perlite, or coarse sand, into a potting soil if using a container. Create French drains in the garden bed, or plant in raised beds on gravel. I have saved herbs from drowning just by re-potting into a gritty cactus mix, or into clay pebbles.
Test drainage performance using simple measures. Dig a 12-inch hole, fill with water. If it wells up and empties away in a couple of hours you have well-drained though not unreasonably draining soil; if it lingers longer, spade the stuff and add more perlite. Who will be surprised at this?, Pour in water after filling a pot with soil: if it rests in pearly pools on the surface for ten minutes or so, remould again and add water.
Make your watering depend upon the drainage, water Mediterranean herbs only when the top 2 inches of soil are dry. For moisture-loving varieties, let the top inch of the soil dry. Always water well, but as infrequently as possible, for the depth of the root is an insurance against rotting.
Read the full article: Best Soil for Herbs: Ultimate Growing Guide
