When and how should you fertilize herbs? Knowing these things is crucial to understanding how to make the most of your delicious herbaceous plants. I mean, that’s why you’d want to grow your own herbs at home, right? But should you even fertilize them in the first place?
Herbs need to be fertilized due to the depletion of soil nutrients over time. It should be applied at the beginning of spring. The feeding frequency depends on 1) light conditions, 2) soil quality, 3) growth stage, and 4) the herb’s health. Indoor herbs commonly require more fertilizer than outdoor ones.
The truth is that you need to fertilize your herbs. However, how frequently? Definitely not as heavily as vegetables. How do you know when to start fertilizing? How to avoid the common overfertilizing mistake? Keep reading to find the answer to these questions and many more.
Lush herbs that grow without any visible development issues generally do not need to be fertilized, but feeding them can help them continue thriving. Herbs that start showing decline and exhibit stunted growth, among many issues, require fertilizer application. This is because soil loses nutrients as it gets absorbed by herbs over time.
A good-looking herb, in general, does not need any fertilizer.
However, good-looking does not imply that your herb is developing at its best and that it will stay like this forever. Moreover, avoid waiting until you start seeing problems.
As I’ve discussed before, the nutrient content in your potting soil is going to run out at some point.
So even if your herb has already been growing in the same pot without fertilizer for a whole year, it is still a good idea to start giving it a balanced fertilizer (a mild 4-4-4, for instance) by then. This applies even if it looks OK.
Fertilize herbs correctly by 1) understanding the ideal time for feeding, 2) choosing the appropriate fertilizer, and 3) setting an application schedule.
Fertilizing herbs is necessary to rebuild the nutrient content in the potting soil that’s lost after getting absorbed while the plants are growing, especially with container gardening. These minerals are known as Nitrogen (N), Phosphorus (P), and Potassium (K).
Keep in mind that herbs can’t produce and provide nutrients for the medium it is growing on by themselves. Hence, herbs need fertilizers containing sufficient amounts of nutrients such as nitrogen, phosphorus, and potassium.
Each fertilizer is often identified by 3 numbers known as N-P-K that determine the percentage of nitrogen, potassium, and phosphorus, respectively.
However, many beginner gardeners make the same number one mistake: overfertilizing. But I’ll talk about that in greater detail later.
1. When You Should Start Fertilizing Herbs (3 Different Cases)
Herbs need fertilizer if they are in their mature stage (older than a few months) and the soil is depleted of nutrient content. This can be determined through an inexpensive soil tester.
If a soil tester is not available, then an herb should be fertilized depending on its soil’s history.
What does that mean? To decide when you start fertilizing, you need to have an idea of how you got that herb, where you got it from, and how long it has been since it was last fertilized.
More precisely, your herbs might fall into one of these cases: supermarket herbs, nursery herbs, and seedling herbs.
Herbs bought in small plastic containers from the supermarket need fertilizer usually straight away, especially basil and parsley. Conversely, immediate feeding is not required for hardy and shrubby herbs like thyme, rosemary, or lavender.
This is because the soil is pretty low in nutrients. Moreover, those herbs need repotting anyway so I just usually change the soil too. Have a look at our supermarket herb guide.
Keep in mind that the new soil you should use for repotting herbs should be a fresh potting mix. You can either do it yourself through this DIY potting soil guide or buy the best available in the market.
Discover my recommendations in our article on the best potting soil!
After the soil transplant with a fresh potting mix, you should start fertilizing after 6 months. Indeed, the majority of potting soils contain nutrients on them that will allow your herbs to thrive for many months to come without any external support.
Herbs from the nursery do not require fertilizer for at least 6 months. The container is of the right size, and the potting mix is very likely to be of top-notch quality.
Seedlings and seeds do not require fertilizer. Indeed, each seed has a package of nutrients (including the N-P-K minerals) that they use to develop. Applying fertilizer to seedlings will likely kill them due to the high salt content unsuitable for early root development.
When the seedling is ready to be transplanted in a larger pot, use a fresh, high-quality potting mix that will guarantee your herb to thrive for at least 6 months without fertilizer (case 1).
2. Which Fertilizer You Should Use for Herbs
To determine which fertilizer is best for herbs, a soil test must be done to identify which nutrients are particularly lacking in the growing medium. Otherwise, a complete or balanced fertilizer is generally safe to use.
If you were able to measure the nutrient content of your soil, then it should be quite easy to pick the right fertilizer for your herbs. Your fertilizer should contain more of the nutrient it is currently lacking so that your herbs don’t suffer from any deficiencies.
For a quick guide on what I mean by this, refer to the simple table below.
|Lacking Nutrient||Ideal Fertilizer Nutrient Ratio|
|All 3 more or less equally||4-4-4|
When only a single nutrient is greatly lacking in your herb’s soil, you could also opt to use pure-element fertilizers to address the deficiency. This is true for all three of them: nitrogen, phosphorus, and potassium.
Personally, though, I do not recommend using them as they easily damage and kill herbs. In the event that you only have them at hand, go really light on the application.
For the most part, any fertilizer application instructions you have on the label are likely for herbs grown outdoors directly in the ground. So only use about half the suggested amount—or even less—for indoor potted herbs.
Many expert gardener will say that fertilizers don’t need to be used following the exact amount suggested on labels. Half of what is recommended is generally sufifcient, especially for indoor herbs because they have a lower metabolic rate due to less sunlight exposure.
Also, if you can’t get your growing medium tested, the safest fertilizer for it would be a low-strength or a mild balanced fertilizer such as the one below on Amazon.
You can also buy fertilizers higher in nitrogen and potassium. These two minerals are generally absorbed at a slightly faster rate by your herbs. A 24-8-16 fertilizer (or a similar ratio), for instance, can be a good choice. One such famous fertilizer is this one on Amazon.
What About Micronutrients in Fertilizers for Herbs?
For good overall growth, herbs and most other plants also require various micronutrients such as iron and calcium in their soils.
To ensure optimal development, check your fertilizer. Look at the label and see if it’s enriched with the so-called micronutrients. These typically include elements like iron, calcium, sulfur, and magnesium.
Don’t worry too much about their exact amount. It’s normal for them to only be available in small amounts, which is what herbs and plants need.
This is because they are absorbed in smaller amounts compared to N-P-K. Nevertheless, they are all still vital for plant development. Hence, if they are included, it is a great plus!
3. How Often You Should Fertilize Herbs
Grown potted herbs need to be fertilized 3–4 times a year, from spring to autumn. Herbs grown in the ground outdoors may need more frequent feeding. Nonetheless, herbs should never be fertilized during the winter months when they are dormant.
More specifically, timely herb fertilization is as follows:
- None in winter: Due to a period of dormancy (or very low activity state), almost no minerals are required for herbs. This does not apply if you are using a grow light and temperature-controlled environment;
- Once (or Twice) in Spring: Herbs go start growing actively at this time, getting ready for the summer;
- Twice in Summer: Here herbs start to fully develop so their nutrient consumption is at its peak. Application at this time is ideally done at the beginning and middle of summer.
- Once (or None) in Autumn: Little fertilization is needed by fall as the fertilizers provided in during the period might end up unused until the next season as herbs start becoming dormant.
Fertilization is not an exact science, especially if you are not performing any scientific method to measure and understand how much or what you need. However, there are a few reliable rules of thumb you can follow to help you know how frequently to fertilize your herbs.
The frequency of your fertilization depends mostly on the amount of light your herb is receiving. During summertime, when your herb is receiving a sustained 6 to 8 hours of sunlight, I would go with 1 light fertilization (half of what is suggested on the fertilizer label) every 2 months.
You can also do so in the winter in case your herb is growing in a closed environment like a greenhouse, grow tent, or basement. In such instances, you can closely monitor and control factors like temperature and lighting so your herbs will grow just fine even in the middle of winter!
Find out how to do it in our article on growing herbs in the basement!
Otherwise, it’s best to not feed your herbs any fertilizer at all—regardless of whether they’re in a pot indoors or outdoors. You see, during cold and low-light winter days, many herbs enter a dormant stage where their growth slows down greatly or stops completely (albeit temporarily).
As mentioned earlier, overfertilization is way more common than under-fertilization. Indeed, pushed by enthusiasm, especially beginners, are more prone to exaggerate.
What is the problem with providing a higher than the suggested amount of nutrients? After all, the more mineral, the better growth you might think, right? Unfortunately, this is not the case.
Indeed, the biggest problem caused by overfertilization is the excessive amount of minerals (those are the nutrients N-P-K) that build up in the soil over time. This is because the minerals that your herb will not absorb will remain in the potting soil in the form of salt. Different from open space, where minerals are recycled way more efficiently and quicker, this is not the case in a closed potted space. There the level of available minerals can raise way more quicker.
Salt is a very bad companion for herbs because it “competes” with them for water. A high level of salt interferes with the proper development of the herb because it holds/absorbs water from the soil leaving the herb without water even if the soil is saturated. In the worst case in which the problem is not spotted in time, and the salt keeps rising, the salt will extract the water from the roots plant itself. This is the extreme case of herb burnt (and that is what you might hear when some more expert gardeners refer to “fertilizer can burn your herbs”).
A second problem, equally important, is “nutrient intoxication.” The herbs will try to absorb as many nutrients as they can. If such minerals are available in high concentration, your herb will suffer a variety of symptoms depending on how much and which nutrient(s) has been absorbed.
Do you want to know more about overfertilization? Click on the image below for a detailed guide on the most common sign of overfertilized herbs. https://yourindoorherbs.com/top-18-mistakes-in-indoor-gardening-you-might-be-doing/
Overfertilizing is one of the most common mistakes among beginner gardeners and plant enthusiasts. This often happens when 1) the fertilizer is applied too early, 2) seedlings are fertilized, 3) application instructions are followed, 4) strong fertilizers are used, and 5) fertilizer is applied to revive herbs.
Let me further explain what I mean!
1. Fertilizer is Applied Too Early
Oftentimes, I hear newbie home gardeners complain about their herbs dying on them when they made sure to fertilize them right away. The problem is many of them aren’t aware that it’s what they’re doing that’s actually killing off their originally already luscious herbs.
Keep in mind that most potting soil used for herbs sold pretty much anywhere already has tons of nutrients. It’s what’s keeping them looking so full and prolific in stores and nurseries!
So providing extra fertilizer that they don’t really need is not going to do them any good. In fact, doing so has the opposite effect on them—you will only damage your herbs.
You need to wait at least 2 weeks up to a couple of months before you start fertilizing those herbs.
2. Seedlings are Fertilized
Seeds generally have all the nutrients a young plant will need to grow packed into them.
Hence, fertilizing them while they’re still just tiny little sprouts will probably kill them due to the high nutrient content you will introduce to their growing medium.
3. Application Instructions are Followed
Another common mistake I see beginner gardeners mistake is religiously following the application instruction printed on their fertilizers’ labels.
One of the fertilizers I recently bought suggests applying fertilizer once a week. This is an insanely high frequency, especially during the winter season. Do that and your herb will have a way shorter lifespan.
In other words, try to resist the impulse of following what manufacturers cay even when common sense tells you otherwise.
4. Strong Fertilizers are Used
You can tell the strength of fertilizers by looking at the concentration of their nutrients. The higher the numbers for N-P-K, the stronger the fertilizer is.
In the market, you can find extremely strong fertilizers with concentration values above 30 that are also usually quite unbalanced, with a single number disproportionately higher than the rest.
An example is what’s called blood meal fertilizer. It can have high amounts of nitrogen, pure potassium, or only phosphorous.
This can be ideal in a specific situation in which you are totally sure that one of the nutrients is totally missing. However, this is hardly ever the case, and you might end up just damaging your herb. It’s better to transplant your herb in fresh potting soil than feed it any of these concentrated fertilizers.
5. Fertilizer is Applied to Revive Herbs
Yellow basil leaves, drooping chives, and many more signs don’t necessarily imply that your herbs need to be fertilized. Reading around and chatting with expert gardeners, I realized that a bad-looking herb is, more often than not, affected by problems totally unrelated to the lack of nutrients in the soil.
I mean, just think about root rot due to excessive watering, hidden aphids or spider mites, and lack of light. These are, by far, the most common problems that affect herbs. In such cases, adding fertilizer will provide neither benefits nor solutions, and doing so might actually make the situation worse.
Pro Tip: If your herb is not growing well, check for other signs that might explain the issue before applying any fertilizer. Ask yourself the following questions:
- Is your beneath-the-surface soil too wet?
- Is the herb receiving enough light?
- Is the ambient temperature too low for that specific herb (like basil in winter in the northern hemisphere)?
Just by addressing these, you are likely to realize what’s the best way to revive your herb without feeding it fertilizer, which can actually exacerbate existing problems if the application is not needed.
How do you fertilize herbs?
The method for fertilizer application will depend on the type to be used. Most commonly, solid and liquid fertilizers need to be highly diluted in at least a gallon of water, creating a solution that is then added to the soil. Pellets need to be mixed into the top layers of the soil and others may need to be placed into spikes.
Does mint need fertilizer?
Mint, just like any other herb, will eventually need to be fertilized, if the soil is depleted of the 3 important minerals and the other micronutrients. Inexpensive and easy-to-use soil testers are available both in online retailers and gardening shops.
Does basil need fertilizer?
Basil needs to be fed an N-P-K balanced fertilizer at the beginning of spring to promote and enhance foliage growth during summer. This is particularly true if the basil is grown in a container and kept indoors.
Summary of Should You Use Fertilizer on Herbs?
Herbs will only need to be fertilized once their growth slows down due to nutrient deficiencies in the soil. Doing so is essential to keep the plant alive and healthy throughout the seasons as soil normally loses nutrients in it after they are absorbed by herbs over time.
The depletion of soil nutrients can be determined through an inexpensive soil test. This will also help gardeners know which nutrients to focus on when selecting the right fertilizer for their herbs. But in general, it is safe to use mild balanced fertilizers for herbs.
More importantly, it’s best to only fertilize potted herbs about 3–4 times a year, starting from spring up until autumn. Outdoor herbs, potted or in-ground, will need more frequent applications. However, herbs should not be given any fertilizer in winter unless they are in a completely enclosed and controlled environment.
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