Are you wondering if you should be fertilizing your herbs? And which fertilizer is best for your specific herb plants?
All plants need nutrients to grow, but most herbs have fairly light nutrient demands. In fact, overfeeding can be as much of a problem as underfeeding.
Read on to learn how to feed smarter, since this is one area where more is not always better.
What Types Of Fertilizer Are Good For Herbs?
You can feed your herbs with a variety of fertilizers: fish-based or seaweed fertilizers are the most common in the gardening community. Compost or worm castings also make an excellent organic fertilizer for herbs.
If all you have is a general commercial fertilizer, then you can still use it to feed your herbs, at a lower concentration.
Fish and Seaweed Based Fertilizers
Fish emulsion is an organic NPK foliar fertilizer that I use on many of my vegetables and a few of my herbs.
Powdered seaweed is a micronutrient foliar fertilizer that I use on all my herbs, even the light feeders. I have friends near the coast who get fresh seaweed and add it to their soil as a slow-release micronutrient fertilizer.
For more information on using seaweed for micronutrients, see How to Use Seaweed Fertilizer.
Compost And Manure
Compost is a slow-release organic fertilizer rich in macro- and micro-nutrients. And you can make it yourself from kitchen and garden scraps without paying anything.
Manure is rich in NPK, often especially N. Most manure has to be thoroughly composted before being added to your garden, but rabbit manure can go on fresh. Do not use human or pet manures.
The fertilizers may also be either lab-synthesized or organic.
I don’t have experience with using synthetic fertilizers on herbs. The Piedmont Master Gardeners recommend using synthetic foliar fertilizers for indoor herb gardens at half the strength suggested on the package.
The Nutrients Our Plants Need to Thrive
Different herbs need different amounts and types of fertilizer. See the list below.
Fertilizers can provide macronutrients, micronutrients, or both. The most important macronutrients are nitrogen (N), phosphorus (P), and potassium (K). NPK numbers are what you’ll see on bagged fertilizers, always in that order. For instance, a mix labeled 10-20-20 contains 10% nitrogen, 20% phosphorus, and 20% potassium.
Sulfur, calcium, and magnesium are secondary macronutrients that are also needed by your plants, to a lesser degree. These two groups of nutrients represent the primary fuels for plant growth.
There are a host of micronutrients that plants need in smaller quantities, such as zinc, iron, and copper. Micronutrient deficiencies will make your plants more vulnerable to temperature swings, drought, diseases, and pests.
How to Feed Your Herbs
Fertilizers can be applied in one of three ways:
- Fertilizer can be worked into or spread on top of the soil, where roots absorb them slowly over a long period of time.
- You can also mix fertilizer with water before watering your plants.
- Spray the mixture directly onto leaves. This approach, called foliar feeding, provides a quicker burst of nutrients.
Should You Fertilize All Your Herbs The Same Way?
No. Different varieties of herbs need different amounts of nutrients to thrive.
While all plants need some nutrients to grow, many herbs are fairly light feeders. This means they require smaller amounts of the three major nutrients nitrogen, phosphorus, and potassium, or NPK.
Some herbs actually have a better flavor when they are grown in fairly poor soil. Herbs that prefer poor/light soil and don’t need supplemental NPK fertilizer include:
Herbs that prefer average soil and don’t need supplemental NPK fertilizer include:
Herbs that prefer moderately rich soil but don’t need supplemental NPK fertilizer:
- Chervil (likes lots of humus)
- Savory (summer and winter)
Herbs that prefer moderately rich soil and also want supplemental NPK fertilizer include:
How Often & When To Feed Your Herbs
Rodale’s Garden Problem Solver recommends giving herbs one application of slow-release macronutrient fertilizer in the spring.
When I dig my perennial herbs up to divide them in spring, I put compost in the planting holes. I add a little compost for light-soil plants like lavender and mint and a lot for heavier feeders like sage and chives.
I also mulch my whole herb garden with a mix of sawdust and rabbit manure in the fall, thus providing one more slow-release feeding to everything.
You could also work in conventional fertilizer at the base of your plants in the spring.
Rodale’s also suggests giving your herbs a foliar feeding with seaweed spray two or three times during the growing season. I have found this helpful.
For the heaviest feeders, garlic, and parsley, Rodale’s recommends a monthly foliar feeding with some kind of NPK fertilizer. I use fish emulsion. Conventional fertilizer would also work.
How to Fertilize Herbs In Containers
Container-grown herbs may need more supplemental fertilizing than ground-grown herbs since the soil they can draw nutrients from is limited.
The Cornell Cooperative Extension recommends giving indoor container-grown herbs low doses of foliar fertilizer every two weeks. When using seaweed fertilizer, follow the instructions on the label for the correct application, starting at the lower end of any range given. If you are using commercial synthetic fertilizer, apply it at 1/4 to 1/2 the standard recommended dose.
Overfertilizing container-grown herbs can be more harmful to your plants than under-fertilizing. So also start at a lower dose when fertilizing your container herbs.
If you have a worm bin, the castings make an excellent fertilizer for herbs. I use vermicompost from my indoor worm bin, which is richer and more concentrated than the compost from my outdoor bin. My indoor chives and rosemary get top-dressed with worm castings in winter.
Common Problems When Fertilizing Herbs
Overfeeding and underfeeding are a little harder to diagnose than underwatering or overwatering. But here are some things you can look for:
Underfertilized plants will have nutrient deficiencies. Their growth may be stunted or their leaves may become spindly, misshapen, yellow, or pale. But there can be other reasons for this.
If your plants are too wet, too dry, too hot, or too cold, they may simply not be able to absorb the nutrients you are giving them. Pests chomping or sucking on your plants may steal the nutrients your plants need.
Too much macronutrient fertilizer–especially nitrogen–can cause herbs to grow large, lush, and very weak-flavored.
Are You Ready To Fertilize Your Herbs?
Most herbs are light feeders, fairly undemanding when it comes to nutrients. Think about the specific species you’re growing and the type of soil you have as you decide how much supplemental fertilizer to use.
Most of all, pay attention to what works and what doesn’t in your particular garden. Experiment, keep records, and do more of what works for you.