Basil leaves died because of downy mildew
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Nutrient Requirements For Hydroponic Basil: Mixing, Fixing and Diagnosing

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Basil is one of the easiest plants to grow in hydroponics. It flavors food and makes the environment more aromatic. Focusing on the nutrient requirements for basil will help you grow a green and lush basil bush, which is the topic of this post.

Basil is a resilient plant. It rarely shows symptoms, but occasionally, you’ll notice withered or yellow leaves. Often, you’ll confuse them with some disease, like fusarium wilt. But it could be a simple nutrient deficiency.

How do we distinguish infection from nutrient deficiency? What are the common symptoms of nutrient deficiency in basil? How do you prepare a perfect nutrient solution for hydroponic basil? How do you supplement nutrients?

Keep on reading to educate yourself on all these matters.

Related: How To Grow Basil Indoors?

General nutrient requirement for hydroponic basil

The only consumable part of basil is its leaves. Besides its edible foliage, some may also enjoy its flowers. This makes basil a perfect choice for hydroponics.

EC for hydroponic basil

Yet, unlike lettuce and other leafy greens, basil demands a more concentrated nutrient solution. While most leafy greens prefer an EC range of 0.8-1.5, basil grows well above 1.5. Basil doesn’t get nutrient burn even at 4.0 EC. Yet, that level of concentration is often unnecessary.

Most hydroponic growers use a master blend of 4-18-38 and calcium nitrate, which is 15.5-0-0. If you do the math, the resulting mix’s NPK ratio is 19.5-18-38. This works perfectly for hydroponic basil, too.

If you use a different fertilizer, ensure the ratio is similar. For instance, you can grow basil using a water-soluble fertilizer with an NPK ratio of 10-9-18 micronutrients.

pH for hydroponic basil

Basil prefers a slightly acidic environment. Basil’s growth is excellent at a pH level of around 6.

Yet, note that mixing nutrients in the water would make the water acidic. Thus, ensure the water is pH-neutral before diluting the nutrients. That is, pH 7.0. Once you mix the nutrients, you’ll see the pH around 6.

You don’t have to be precise. Basil, in particular, can tolerate a little more than other plants. Aim for a pH of around 5.8-6.4.

Common nutrient deficiency symptoms in basil

Nutrient deficiency in hydroponic basil is very rare. That’s because the plant has direct access to nutrients in an easy-to-absorbed form. For instance, nitrogen in hydroponic nutrient solutions is either in nitrates or ammonium form. Further, the nutrient level is something we can easily control in hydroponics rather than in soil.

Basil’s nutrient requirement is straightforward because it is not a fruiting or rooting vegetable. It’s an herb we grow for its leaves.

Often, if there is a nutrient problem in hydroponic basil, there are two significant reasons.

One reason is that the EC level is too low. Rainwater may enter the container and dilute the solution if you grow basil in outdoor Kratky containers. Another reason could be growing basil along with other plants. For instance, you can grow basil with lettuce. However, basil may show some symptoms because the concentration of the nutrient solution is specific to lettuce.

The other reason is low levels of the nutrient solution itself. Again, the water level may go down fast in passive systems like Kratky. Before you even notice, the plant is withered and turns yellow. Even in circulating systems, there can be reasons like system clogs that block or reduce the nutrient flow.

In all these instances, the symptoms are similar. Initially, you’d see a withered plant, and the leaves may turn pale yellow. The discoloration is prominent in the more matured leaves. This is because of nitrogen deficiency. But very soon, the entire plant will show similar discoloration. Eventually, you’d see the leaves dry up and fall off.

If you still suspect a nutrient deficiency, it may be due to a wrong choice of fertilizer. Here’s a list of symptoms and possible causes adapted from this post. You might have to change the nutrient solution, add supplements, or foliar feed with the correct fertilizer.

SymptomPossible Nutrient Deficiency
Chlorosis, inhibited growth, necrosis, stunted rootsN Deficiency
Slender and smaller leaves with olive-green spots, marginal necrosis, leaf abscissionP Deficiency
Stunted leaves, leaf yellowing, scorching, freckles in central part of leavesK Deficiency
Slight stunting, irregular leaf shape, narrow leaflets with lighter green colorationCa Deficiency
Small-sized leaves, chlorosis from edge to center, curling leavesMg Deficiency
Slight overall loss of green coloration, fragile and yellowing foliageS Deficiency
Overall foliage discoloration (netted chlorosis), burned tips, stunted rootsFe Deficiency
Stunted roots and leaves, downward curling of marginsMo Deficiency
Source: Characterization of Physiology, Photosynthesis, and Nutrition Based on Induced Deficiencies of Macro- and Micronutrients in Basil (Ocimum basilicum L.)

Mixing nutrients to meet basil’s nutrient requirements?

Most fertilizers designed for hydroponics work well for basil. For instance, the master blend 4-18-38 with equal calcium nitrate does the job. You may use diamond spec T with equal calcium nitrate outside the US for similar results.

Part A of the solution contains the macronutrients nitrogen, phosphorus, potassium (NPK), and most micronutrients except calcium. You should have ample nitrogen in the final mix because it stimulates foliage growth. However, since Part B always has calcium nitrate, which has 15.5% nitrogen, you can choose a fertilizer with low nitrogen. Both Masterblend 4-18-38 and Diamond Spec T are good fits for this.

If you’re part A and don’t have enough magnesium, you also need to mix Epsom salt.

Take equal weight of fertilizers for parts A and B and dilute them separately in the same amount of water. If you’re part A lacks magnesium, mix Epsom salt into your part A. This needs to be half the weight of your part A.

We can now mix it in your nutrient reservoir. Fill the reservoir with pH-neutral water. You can use a digital pH meter or pH strips. You may have to use pH adjusters if it’s not in the neutral range.

Now, mix some of the part A you’ve prepared. Note the amount of part A you’re mixing. Then, mix the same amount of part B. Now, check the solution’s EC. You have to repeat this until you read 2.4 EC. Your solution’s pH would have reached the 6-6.5 range by now.

Nutrient deficiency or infection?

When facing issues with hydroponic basil, growers should first observe the pattern of symptoms.

Uniform symptoms that affect the entire plant similarly suggest a nutrient deficiency. For example, an iron deficiency is likely if newer leaves are yellowing while older leaves remain green. Conversely, nitrogen deficiency might be the culprit if older leaves are yellowing first.

Discoloration and leaf curling in basil not meeting it's nutrient requirements.

On the other hand, if symptoms appear as localized spots, lesions, or patches and spread from specific points, an infection is more probable. Distinct spots or mosaic patterns, sudden wilting, and abnormal growths are telltale signs of a pathogen presence.

Related: Hydroponic Basil Pests and Diseases

Additionally, nutrient deficiencies usually lead to more generalized symptoms like chlorosis, stunted growth, necrosis, and leaf shape changes, whereas infections result in more localized and varied symptoms.

Related: 9 Reasons Why Hydroponic Basil Wilt


Basil grows well in hydroponics, given the correct nutrient mix. Most popular hydroponic fertilizers do the job. Ensure that the plant has enough contact with the nutrient solution and that its EC is above 1.5. The pH of the nutrient solution could be around 5-5.6, as it is for most other plant.

We recommend changing your fertilizer rather than supplementing or foliar feeding if you notice specific nutrient deficiencies. These other techniques are often complex and unnecessary.

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