Gardening
Herbs
Not all herbs have the same fertilizer needs.
By
Nadia Hassani
Nadia Hassani
Nadia Hassani is a a Penn State Master Gardener with nearly 20 years of experience in landscaping, garden design, and vegetable and fruit gardening.
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Updated on 07/01/24
Reviewed by
Kathleen Miller
Reviewed byKathleen Miller
Kathleen Miller is a highly-regarded Master Gardener and horticulturist with over 30 years of experience in organic gardening, farming, and landscape design. She founded Gaia's Farm and Gardens,aworking sustainable permaculture farm, and writes for Gaia Grows, a local newspaper column.
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When it comes to fertilizer, herbs, unlike vegetables, are not heavy feeders. The fertilizer needs depend on the type of herb, the growing conditions, and the texture and fertility of the soil.
To follow the basics about fertilizing herbs you need to know what type of soil you have—sandy, loamy, or clay soil—and also, its composition of nutrients. A soil test is the only way to find out what your soil might be lacking for healthy plant growth.
Herbs grown in pots indoors or outdoors and hydroponic herbs have different fertilizer needs than the herbs in your garden. Read on to learn more about fertilizer for herbs.
Do Herbs Need Fertilizer?
The short answer is, yes, herbs need fertilizer. However, not all herbs have the same fertilizer needs. Herbs roughly fall into two groups:
- Slow-growing herbs with small leaves or needles and fibrous, woody stems: Many of these herbs are native to the Mediterranean, where they grow in dry, infertile soil. They are usually perennials such as bay laurel, culinary lavender, mint, marjoram, oregano, rosemary, sage, savory, tarragon, and thyme.
- Fast-growing herbs with larger, thinner leaves: These include annuals such as basil, borage, cilantro, chervil, and dill; biannuals such as parsley; and perennials such as chives.
Herbs in the first group generally need less fertilizer than herbs in the second group.
What Type of Nutrients Do Herbs Need?
Start by planting herbs in healthy soil rich in organic matter. In addition, they will benefit from an organic complete, slow-release fertilizer containing equal amounts of the macronutrients nitrogen, phosphorus, and potassium. A slow-release fertilizer is especially important if your garden has sandy soil because nutrients wash out quickly.
To give fast-growing herbs an extra boost, apply fish emulsion, which is an organic fertilizer high in nitrogen, with an NPK ratio of 4-1-1 or 5-1-1.
How Often Should I Fertilize Herbs?
The growth pattern of the herb determines the frequency of fertilization. In soil of average fertility, it is usually sufficient to apply a complete granular fertilizer in the spring when the herb breaks dormancy or when the new growing season starts. Water immediately after fertilizing to prevent fertilizer burn.
For other herbs, a light monthly application of a slow-release complete fertilizer should be enough. However, if the leaves start to look yellow, it may be a sign of nitrogen deficiency. In that case, applying fish emulsion is a quick fix. Before you reach for the fertilizer bottle, rule out that the yellowing of the leaves is not caused by something else.
How to Fertilize Herbs in Containers
Herbs grown in containers need fertilizer applications more often than herbs in garden soil. With the frequent watering that container plants require, the fertilizer in the potting mix washes out more quickly. Just as with sandy soil, it is important to use a slow-release fertilizer.
The roots of container plants grow in a confined space, unlike herbs grown in garden soil or raised beds. Using synthetic fertilizers, which contain a high level of salt, can lead to over-fertilizing. That's why organic fertilizers are preferable. To prevent fertilizer buildup, it is best to use the fertilizer at half the strength of what is specified on the label.
How to Fertilize Hydroponic Herbs
The fertilizer requirements for hydroponically grown herbs are quite different from herbs grown in garden soil or potting mix. They need regular and frequent fertilization, every two weeks or as specified in the directions of your hydroponic system, using a special hydroponic fertilizer for vegetables and herbs.
Hydroponically grown basil is susceptible to magnesium deficiency because the water in which the plants are grown or the added fertilizer does not supply enough magnesium. This micronutrient deficiency manifests itself as chlorotic yellowing leaves, typically between the leaf veins. To fix it, add a liquid magnesium supplement, which is usually sold as a combination of calcium and magnesium, and follow the instructions on the label.
Is It Possible to Overfertilize Herbs?
Adding too much fertilizer to herbs usually leads to an excess of nitrogen, which has undesirable results, especially for slow-growing herbs. For basil and other thin-leaved herbs, the fast leaf growth induced by nitrogen is fine because you want your plants to be lush. For rosemary and other Mediterranean herbs, however, rapid growth means that there is less concentration of essential oils causing the herbs to become less aromatic, and have a weaker flavor.
Prevent overfertilizing your herbs with the following tips:
- Use a slow-release, preferably organic fertilizer, which has a lower nitrogen concentration than synthetic fertilizer.
- Do not fertilize herbs more often than recommended.
- Fertilize herbs in containers with fertilizer at diluted strength.
All herbs benefit from applying a 1-inch layer of compost around their base, which is a safe way of adding nutrients to the soil without risking overfertilization.