A culinary classic that can be grown in the garden or on your kitchen counter, basil can sometimes be tricky to care for. Pinpointing what is wrong can seem impossible, but with some careful observation, specific symptoms can be easily seen.
The most common problems growing basil include symptoms like small, yellow, curling, or wilting leaves along with pest and disease issues like holes or translucent, white, brown, and yellow spots that begin to occur on the leaves’ surface.
It may also be that it lacks the correct water, nutrients, or amount of sunlight causing the basil plant to struggle growing, which contributes to leggy plants and encourages it to flower.
From its leaves to its roots, this article is here to help you diagnose and cure 14 of the most common problems growing basil!
1. Yellow Leaves
Instead of a deep green, the plant has a yellow hue to its foliage, or you begin to notice yellow spots appearing on its leaves.
A lack of water, excess water, poor soil nutrients, unfavorable seasonal climate, fungal diseases, and incorrect soil pH are all causes of yellowing leaves.
Adjust the growing environment’s moisture levels, sunlight, and temperature if possible. Testing the pH of your soil and applying a general organic vegetable fertilizer is a great place to start.
2. Small Leaves
A standard basil plant will have leaves that normally grow from 2 to 4 inches in length. If you notice it is consistently growing smaller leaves than this, it most likely has a growing issue.
Insufficient nutrition in the soil, a lack of sunlight, or a lack of growing space leads to small leaves.
Add supplemental light, or move the plant to a sunnier location. Aim for a goal of 6 to 8 hours of daylight, and fertilize your basil plant regularly to prevent small leaves due to lack of energy and nutrition.
If your plant hasn’t been repotted in the past year, replant it into a larger pot so it has more room to grow.
3. Leggy Plants
If your basil plant seems to be growing long stems with leaves that it can barely hold up, it is most likely lacking strong sunlight or adequate nutrition.
Long, leggy stems are usually caused when a plant reaches for sunlight or has too high nitrogen levels in the soil.
Try to provide supplemental lighting, and discontinue the use of fertilizer so the soil can reach a balanced level of nutrition.
4. Black Spots on Basil Leaves
You may notice black, sooty spots that appear on the top and bottom of the leaves caused by a bacterial infection.
Bacterial leaf spot (Pseudomonas cichorii) affects the leaves when infected soil debris land on the leaves of the plant. Downy mildew (Peronospora belbahrii) is a water mold with the appearance of black, sooty spots.
Reduce watering, and make sure there is plenty of air exposure to all of the leaves. An organic neem oil spray can help to prevent it from establishing on your plant; however, there is no total cure.
5. Brown Spots on Basil Leaves
If you begin to notice brown spots forming on the mature leaves of your basil plant, it has most likely been caused by too much moisture in the area.
Bacterial or fungal infection and stagnant water on the leaves’surface may cause it to cultivate fungal spores that kill the leaf in some areas.
Fusarium wilt (Fusarium oxysporum f. Sp. Lycopersici) is a common fungal infection and can be terminal for the plant if left untreated.
Reduce watering, and try to only water the soil and roots while avoiding drenching the leaves. Apply an organic copper fungicide weekly if fungus is suspected.
6. White Spots on Basil Leaves
White, fuzzy spots that appear on the top and bottom of your plant’s leaves can cause it to lack the ability to photosynthesize.
Hot and dry environments will cause powdery mildew to thrive when water remains on the leaves’ surface. The spores can then travel by water and air to other leaves, quickly overtaking a plant.
Avoid allowing water to remain on the leaves for too long, and apply organic neem oil to help coat the leaf’s surface and prevent spores from sticking to it.
7. Translucent Areas on Leaves
While most basil leaves are green, you may notice some with spots that appear translucent, lacking the chlorophyll to give them color.
Chlorosis, the lack of chlorophyll, can be caused by a nutrient deficiency, pests, incorrect watering, or a lack of sunlight.
Pests like spider mites, aphids, or whiteflies suck out the chlorophyll when feeding on the leaves.
Increase sun exposure, moderate the soil moisture, and increase soil nutrition with a general organic fertilizer. Organic neem oil and ready-to-use pest sprays are best for general pest prevention.
8. Curling Leaves
The edges of the leaves will begin to curl if pests establish or environmental stressors create a harsh growing climate for the leaves.
Fungal diseases, inconsistent temperature, inconsistent watering, poor soil nutrients, lack of lighting, and pests like aphids can all contribute to this problem.
Apply a general organic vegetable fertilizer to provide adequate nutrients for growth, and water the plant with 1 to 2 inches of water per week. Relocate the plant or shelter it if possible to remove any wind or intense heat and sunlight.
9. Wilting Leaves
An overall lack of strong leaves or an appearance of low vigor could be signs that your basil plant is stressed.
Wilting leaves can be caused by a lack of water or heat stress. Fusarium wilt also causes a basil plant to show wilting leaves while the soil appears to be adequately saturated.
Ensure your basil plant receives at least 1 to 2 inches of water per week, more if the plant is large or during hot spells. If the soil appears overly saturated, let it dry out until it is dry 1 to 2 inches deep in the soil.
10. Holes in Leaves
Tiny or large holes appearing on your leaves usually indicate that a pest has had a meal! If you notice holes that don’t appear to be bite marks, it could be a fungal infection.
Caterpillars, grasshoppers, beetles, slugs, and fungal leaf spots cause part of the leaf to turn brown, dry out, and then disintegrate away leaving holes in the surface.
Caterpillars are treatable with B.T. (Bacillus thuringensis), and organic neem oil can prevent other feasting insects while copper fungicide helps with a fungal infection.
11. Losing Leaves
If the plant appears to be dropping its leaves but not growing new ones or has a lack of vigor, it could be stressed by its environment.
Overwatering, underwatering, and excessive heat are the main reasons for the loss of leaves. When a plant is forced to reserve its resources like water and nutrients, it will begin to sacrifice the older growth for newer growth.
Adjust watering based on how the soil feels. Water your basil plant with at least 1 to 2 inches of water per week or more during hot spells. If you can, move the plant, or add a light shade cloth if intense heat is expected.
12. Poor Growth
Basil will grow vigorously during the spring and summer. Ifit isn’t, it is most likely an issue with the soil’s nutrient levels.
Basil plants are mostly green vegetative growth, so they need ample amounts of nitrogen. Harvesting too much of the plant continuously will reduce its ability to create energy by photosynthesizing, reducing its ability to grow overall.
Fertilize your basil plant at least once per month with an organic vegetable fertilizer that has an NPK of around 5-4-2. Basil is more productive as a large plant, so allow it time to mature before harvesting leaves.
13. Stem Discoloration
Over time, you may begin to see that the stem is no longer tender and green but turning tan or brown and has become strong and woody. This is its natural growth pattern, but if the plant also shows signs of stress, it could be a fungal infection.
Stem discoloration will happen naturally as the plant ages, turning herbaceous soft tissue into hardy tissue like shrubs and trees have. Other reasons for discoloration include fungal infection and root rot.
Reduce watering, and treat with an organic copper fungicide to allow the soil to dry and mitigate any living spores around.
Among its lush green foliage, you may begin to notice white florets of flowers that grow from the outermost branches. These are the plant’s flowers, and it is a sign the plant has reached maturity or is undergoing stress.
As basil ages, it will begin to produce flowers when it reaches maturity. It may also begin to flower if stressed because it is attempting to reproduce before dying due to temperature and light fluctuations or unbalanced soil nutrients.
If the plant is healthy and has reached maturity, prune off flowers at the base right above the two leaves that sit under the flower stalk. This will help the plant focus its energy on growing leaves.
If the plant does not look healthy, fertilize it with an organic vegetable fertilizer. Also try to reduce any intense heat, strong sunlight, drought, or other environmental stressors.
While it is always worrisome to see a less-than-healthy basil plant, it may just be in need of some diagnostic care. Take a close look at your basil plant, and compare it to the issues and solutions on the list above. Odds are that it’s an easy fix and your basil plant will be back to its bountiful aromatic self in no time!