% Basil is an easygoing plant, but there are instances when its growth is stunted. Here is how to avoid basil growing slowly.

5 Reasons Why Hydroponic Basil Grows Slowly

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Basil, an herb whose leaves are the primary consumption material, is ideal for hydroponics because it is easy to grow and harvest. Most people grow basil indoors in hydroponics, too. So they get fresh basil leaves right from their home garden every time.

Basil usually grows several inches every month. It’s ready for harvesting after only two months when it’s about 6-8 inches high. For hydroponic growers, this means one month from the transplant, as basil seedlings spend one month in the nursery. After the initial harvest, basil usually grows fast, and the successive harvests can be done every two to three weeks.

Related: How often can we harvest basil?

Basil grows from seedling to Maturity in one month.

Yet, sometimes, basil grows slowly or never after a certain point. This happens to both home gardeners and industrial growers. Stunted growth isn’t specific to hydroponics. Some of the reasons outlined here are also relevant to soil-based gardens.

Why does hydroponic basil grow slowly?

Here are the top 5 reasons basil doesn’t grow as intended and how to fix them.

1. Low light

There’s a reason why this is listed as number one. Almost always, this is the reason why basil doesn’t grow well.

Basil is a plant that evolved in the tropics of South Asia. It loves warm weather, full sun, and high humidity, making it a perfect crop for countries near the equatorial line. A healthy basil plant needs at least six hours of direct sun, and some varieties, especially the purple ones, need even more light.

Related: How Much Light Does Basil Need?

Without much sun, basil won’t have its flavor or aroma. Red and purple varieties won’t be able to produce the pigments that make them colorful, too. Without light, you grow some wild weed for no reason.

But the most important sign is slow growth. Basils under shade grow less than an inch every month.

Basil plant under full sun light

The fix for low light is moving the plant to a sunny location or installing grow lights. Move the plant to a location with at least six hours of direct sun exposure. If supplementing with a grow light, you must provide light for at least 10-12 hours daily.

2 Root rot

Root rot is a prevalent issue in hydroponic basil, especially in the Kratky method. It’s rare in circulating or aerated systems.

The prime reason for root rot is the lack of oxygen around the root. When there’s little oxygen, fungi like Pythium take advantage of this and proliferate. Soon, part or all the roots become rotten.

Related: Fixing Root Rot in Hydroponic Basil

The first sign of root rot is slow growth. An infected root prevents the plant from taking nutrients, so there will be little growth. Slowly, the plant will start to show symptoms of other nutrient issues. Then, the plant will wither, shed the leaves, and eventually die.

Although basil is a relatively resilient plant and recovers from root rot when the oxygen level is restored, it isn’t immune to root rot. Surely, root rot will slow down growth.

Root rot in hydroponic systems is easy to fix. If growing basil using the Kratky method, you must ensure that at least 4-6 inches of roots are above the nutrient’s surface level. In other systems, root rot is mainly caused by the choice of growing medium. Mediums, like grow sponges, retain water for a long time. Use something like coco peat pallets. Basil grows excellently in coco peat.

If you see severe root rot, first cut off the rotten parts of the root. Then, try diluting 3% hydrogen peroxide and spraying it directly into the roots.

Root rot can also happen when basil grows in the soil. This is because water remains near the roots without draining. It happens very often when you overwater the plant or if it is exposed to continuous rain for several days.

3 EC level too low or incorrect nutrient mix

Basil grows well on EC levels above 1.5 and doesn’t get nutrient-burned even at 4.0 EC. Thus, it’s best to maintain the EC levels between 2.5 and 3.

Yet, there is one catch in going with this general guideline. Every fertilizer is different. Thus, you must experiment and find the perfect EC levels for your fertilizer.

The other issue is incorrect fertilizer. Fertilizers targeted at soil-based plants or specific for fruiting or root vegetables don’t do well on basil. Plants whose leaves are primary harvest material need more nitrogen than phosphorus. Hence, a balanced NPK won’t work with hydroponic basil. Increasing the EC levels of the solution with a fertilizer that has only a small amount of nitrogen is no good.

The A and B solutions are a concern when considering high nitrogen levels. Most hydroponic growers use this kind of two-part solution. Unlike soil-based growing, Calcium nitrate (Part B) is supplied separately in hydroponics. In high concentrations, calcium nitrate will react with Part A, and the heavy metals may start to precipitate. To avoid this, Parts A and B are dissolved and diluted separately. Then, they are mixed in equal amounts in a large nutrient reservoir, one at a time.

The nitrogen percentage in Calcium nitrate is 15.5%. Yet, it can vary based on the chemical’s purity. Nonetheless, since Part B has high nitrogen levels, part A is chosen to have significantly less nitrogen. This doesn’t mean the basil doesn’t need nitrogen much. The total nitrogen level after mixing parts A and B is still higher.

Master blend 4-18-38 and Calcium nitrate are good choices for Parts A and B. You can use Diamond Special T in Australia for Part A. Although Part A has only 4% nitrogen, together with Calcium nitrate, it makes 19.5% of the final nutrient solution.

It’s tricky to find an excellent single-part nutrient solution for basil. But generally, the ones that grow leafy greens should work.

Hydroponic basil should receive a suitable nutrient solution mix with a 2.5 – 3 EC concentration. Also, keep checking the EC and pH of the nutrient solution regularly.

4 Growing alongside a mature plant

Of course, in hydroponics, there’s no competition for nutrients. Nutrients are readily available to the plant; we supply them directly to its roots.

But there’s a blind spot to this claim.

If you grow two basil plants in a Kratky system, and one is more mature, the younger one may become weak. This is because the larger one with a greater root mass will drink more nutrient solution than the other. Thus, the younger plant will not survive as the water level goes down too fast because of a still-developing root system.

You must place your basil at least a foot away from the other plants, even on other systems. That’s because if the nearby plant outgrows the space it is supposed to take, the basil will need more light. Even with grow light, you can’t supplement when a nearby plant’s foliage is blocking the light.

This is a prevalent issue when growing basil as a companion for other plants. I grew basil as a companion for pak choi. Although they were all planted on the same day, pak choi outgrew the system quickly.

When basil competes for light with the other plants, it grows taller and thinner.

5 Diseases

When the plant has enough nutrients to grow in hot and sunny regions, basil rarely gets infected. But they aren’t immune to many diseases. After all, it’s only one part of the entire ecosystem.

Some diseases that can stunt basil growth include Downy mildew, Fusarium wilt, curly top disease, and Bacterial leaf spot.

Related: Hydroponic Basil Pests and Diseases

Downy mildew starts with yellowing leaves and progresses to fuzzy grayish-purple sporangia on the undersides. Fusarium wilt presents with stunted, wilted plants and yellow leaves, progressing to brown streaks and a sudden leaf drop. Curly top disease, transmitted by the beet leafhopper, causes stunted growth, leaf crumpling, and yellowing, impacting yields in open fields. Bacterial leaf spots show water-soaked brown and black spots on leaves and stems, devastating seedlings even if less severe in field conditions.

Treatment differs for different infections. But most often, you can prevent such diseases by growing basil in a controlled environment and harvesting it regularly. The controlled environment disconnects it from outside insects. Also, when you regularly harvest basil, it creates more space between the leaves. With better airflow, the chances for powdery mildew attacks are minimal.

Why does basil grow slowly after pruning?

Basil growing in ideal conditions would regrow and be ready for harvest two or three weeks after pruning. Basil doesn’t grow after pruning or harvesting for the same reasons mentioned in the last section. Besides, here are a few more specific to pruning.

Related: How To Prune Basil For A Flavorful, Bushy Plant Forever

The most common reason for stunted growth after a harvest is an infection. If you use uncleaned pruning scissors, the plant will become infected. Depending on the severity, you may or may not recover the plant. First, to prevent such things from happening, you need to wipe the running scissors with a disinfectant every time you move from one plant to the other. But if the infection is already there, the best bet is hydrogen peroxide. Dialute some 3% hydrogen peroxide and spray it around the cut and the nearby foliage. You may see them grow better in a few days.

The other common reason is cutting too low. Every time you harvest basil, you must leave at least one set of leaves in each stem. It’s near these leaves, and basil will grow new branches. The plant has no way or reason to grow if the stem has no leaves.

When harvesting for the first time, people often leave the cotyledon and cut the first true leaves. Basils don’t grow near the cotyledon. So, you must leave the first true leaves. For best results, leave two sets of leaves.


You can hardly go wrong with basil. Yet, growing basil can still be challenging for people in colder climates and areas lacking sunlight.

This post outlined five common reasons basil grows more slowly than it should. But there are more comprehensive lists of reasons for stunted growth in basil. Besides the regular reasons, sometimes, people find basil not growing after pruning. This post has touched on those reasons as well.

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