Why Do My Herbs Have Mold and Mildew?

New growth on a Sage plant being hand-pinched
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A benefit of growing herbs is that they do not suffer many of the problems that flowers and vegetables do. Something that you might face is the problem of mildew or mold. Both of these things can damage and kill even the most prolific herbs.

How to Spot Mold and Mildew on Herbs

Herbs need proper ventilation and sunlight to prevent the kind of environment that molds and mildews like. One of the common mistakes many beginning gardeners make is overplanting. As the plants grow larger, they will crowd each other and receive less air circulation and sunlight, which is vital for evaporation. Too much moisture on the leaves and stems leads to mold and mildew.

  • Mold appears on plants as a slimy, brown or black area. You will notice this on the leaf or stem.
  • Mildew is a powdery or fuzzy grayish patch. This most often occurs on the leaves but can become noticeable on the stem as well.

If you see either of these signs on your herbs, there are some emergency steps that you should take. The primary goal is to prevent them from doing more damage and possibly killing your herb plant.

Eliminating and Preventing Mold and Mildew

When you notice mold or mildew in your garden, it is best to act fast. An infected leaf can quickly become an infected plant and, if ignored, the problem can spread to other plants.

  • Prune off the affected area - This is as simple as pinching off the leaves where you see mold or mildew or cutting entire stems that show damage. Be sure to wash your hands before moving to a healthy plant and don't drop the moldy leaves onto the soil. Dispose of them away from your garden.
  • Thin the foliage and possibly the plants ​- This will improve air circulation, so cut down the bushiest parts of the herbs to give them more room. If necessary, move an entire plant, so its neighbors have more space to breathe.
  • Water less often- You may be overwatering and inadvertently allowing the moisture-loving molds to proliferate. Don't water on a schedule. Instead, learn to recognize the signs that your garden needs water.
  • Water only the roots - Unless the summer winds are kicking up a lot of dust, do not water any part of your plants that are above ground. Water the base only and give the roots a healthy dose of water.
  • Remove the entire plant - Sometimes, removal of the plant is necessary. If you find that all of the simple changes mentioned already do not improve your herb's health, you may have to remove and relocate the plant. Consider it quarantine and place it in a pot until it is healthy again.

    Don't Turn to Chemicals

    Whatever you do, don't use a chemical fungicide. Herbs are not your flowers, and they are grown to be consumed. 

    While it's very tempting to run to the nursery for a chemical solution at the first signs of mold, resist the urge. You must remember that you're (probably) growing herbs to use in your kitchen or for their medicinal benefits. This means that you're also likely to use the herbs fresh from time to time. Even if you dry your herbs, those chemical compounds can linger.

    The last thing you want in your spaghetti sauce is a bunch of oregano that's been sprayed with chemicals, right?

    Some gardeners may turn to organic fungicides, but even that may not be the best idea. The best approach to mold and mildew on herbs is the most natural. It does require a little more work, and you do need to pay attention to your plants, but that's part of having a successful garden. The rewards outweigh the work, so please avoid the chemical shortcuts.