7 Reasons Your Basil is Dying and How to Fix It
While basil is one of the easiest summer herbs to grow, it's not immune to common problems. If your basil is dying, you don’t have a black thumb; it likely needs a shift in cultural conditions or may be a victim of pests or diseases. Gardening expert Katherine Rowe outlines top basil problems to watch for and fixes if they crop up.
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Basil is an easy summertime herb that thrives in warm weather. The sun-loving annuals likely originate in the subtropical regions of Southeast Asia and Africa, though the ancient herb has been in cultivation for so long, it’s difficult to discern. The world travelers spread through historic trade routes and colonialism to brighten the plate across cultures.
Basil develops quickly from seed, and its vigorous growth takes off as spring turns to summer. Plants are leafy and bushy, and the more we harvest, the greater the rewards with flushing new growth. While one of the easiest herbs to grow, basil is not free of ordinary garden woes.
Whether growing one of the many varieties indoors or out, common basil problems may crop up. To get to the reasons behind a dying basil, scout for a few primary issues and cultural conditions to determine a remedy.
Sun Exposure
The first critical cultural component for Ocimum basilicum is ample sunlight. They prefer full sun (six or more hours of sunlight daily) to flourish, but will tolerate partial shade (four or more hours of sun daily). Basil needs enough sun to collect all the energy it needs to grow quickly in a single season. If yours lacks vigor and shows pale leaves, leggy stems, and slowed growth, it may be in too much shade.
Lack of light is a common reason for indoor basil to exhibit dying leaves. The herb grows indoors year-round, though it can be a challenge to get the lighting to meet its outdoor standards. Shading also occurs in garden beds or pots as surrounding crops grow tall and block the sunlight from the lower-growing leafy annual.
In hot climates with intense midday sun, you may see leaves turning yellow and brown with crispy edges. This is a sign of sunscald, when leaves get sunburned by direct rays. Move them to bright shade or dappled light during the hottest part of the afternoon, or place a taller specimen on the southwest side to shield the rays.
Too Much Fertilizer
Fertilize the herb at planting and then only once or twice during the growing season. Fertilizing too frequently or in high amounts yields quick growth that releases the flavor in the leaves. You’ll have bushy plants with weaker stems and less taste.
Basil prefers organically rich soils. Amend the beds or potting mix with compost to boost nutrition, aeration, and moisture retention. Compost helps improve sandy compositions and aids in drainage for clay bases. Apply an organic fertilizer like 5-10-5 at planting, and once again about two months later.
For indoor pots, use a liquid feed at half-dilution every four to six weeks for steady nutrition. For potted basil outside, apply it every three to four weeks during the growing season.
Not Pruning
Basil benefits from regular harvests to promote new growth. Pick the leaves or take the upper stems with two sets of leaves. Avoid reducing growth too much early on for a steady, continual flush. Prune stems above a healthy pair of leaves, and new growth emerges at the node within about a week.
By mid-to-late summer, you’ll likely see white bloom spikes form, followed by seeds. Flowering detracts from the flavor of the leaves. As the plant directs energy into reproducing instead of leafy growth, leaves develop a bitter taste. Aging stems become tough and woody. To retain fresh growth and flavor, pinch off blooms as soon as they emerge.
Some varieties like ‘Everleaf Emerald Towers’ and ‘Lettuce Leaf’ are slow to bolt, flowering much later than classic sweet basil varieties like ‘Genovese.’ Others, like Tulsi holy basil and ‘Cardinal’, produce ornamental blooms in pinky-purple and red, respectively. Enjoy the blooms on the bush and in the vase. They’re also a bee magnet.
Water Issues
Ocimum basilicum isn’t overly finicky about water needs and matches many other herbs and vegetables in its requirements. It does best with consistent moisture throughout the growing season, and well-draining soils are essential for overall health. But, damp situations from overwatering lead to pest and disease problems. Underwatering and dry spells, on the other hand, result in energy conservation and halting growth.
When soils are dry to the depth of about an inch or two, it’s time to water. Containers with full-grown plants dry out quickly in the summer heat. Depending on your climate and pot size, they’ll need water more frequently than in-ground selections.
Cool Temperatures
Basil needs warm days and nights to grow. It’s easy to get eager and transplant them outdoors while there’s still a nip of spring in the air. They do best with daytime temperatures in the 70s and nighttime above 50°F (between 10 and 21°C).
If your basil experienced damage from a late-season frost, trim back damaged, brown growth to a healthy green stem, just above a leaf node. If a frost is in the forecast, cover the annual with straw, a bucket, or a plastic container for the night. The herb is very frost sensitive, with the exception of slightly hardier types like Tulsi holy basil, which tolerates light frost.
Diseases
Common fungal diseases can be a primary cause of why a basil plant is dying. Fungal problems arise from cultural practices that harbor spores and promote their spread.
If you’ve had a history of problems, look for disease-resistant varieties. Basil has its own specialist fungal diseases to watch for: wilt and basil downy mildew. Look for ‘Aroma,’ ‘Newton,’ ‘Prospera,’ and ‘Rutgers Obsession,’ among others, as resistant varieties.
Fusarium Wilt
Fusarium wilt in basil (Fusarium oxysporum f. sp. basilicum) is a fungal disease that causes wilting or dying leaves, blackened leaves and stems, and quick decline. Basil grows normally until it reaches six to twelve inches, when it begins to stunt and brown. Wilt spreads from spores in the soil and can come with infected seeds or transplants. Wind, water, and garden tools also spread the spores. The fungus impacts the roots and affects nutrient and water uptake. With fungal wilts, you may see one half of the plant wilting more than the other.
Unfortunately, there’s no treatment for wilt. Remove and dispose of the affected herb, keeping it out of the compost pile.
Basil Downy Mildew
Basil downy mildew is on the rise and first appears as slight yellowing that spreads between leaf veins. It shows in older leaves first, which turn yellow and brown. Flipping the leaf over, you may see dark, fuzzy spots that are fungal spores.
Basil downy mildew is most prolific in high humidity and damp conditions, and leaves may start dying more rapidly when overly wet. Prolonged rains, warm weather, and water splashing on leaves promote the fungus.
This specific downy mildew (Peronospora belbahrii) doesn’t have an effective treatment through chemical applications. Pluck the infected specimens and compost them. This one only infests its living basil host and won’t harbor in debris.
Root Rot
Like mildews, root rot occurs in warm, humid conditions and overly wet situations. Pythium or Rhizoctonia can impact in-ground or potted specimens, depending on the watering regime and environment. The pathogens impact feeder roots, which then can’t absorb water and nutrients. Signs of root rot include drought-stressed leaves that turn yellow and wilt. Branches begin to die back at the tips. Roots will have brown lesions or become completely brown and mushy.
To prevent root rot, ensure well-draining soils. Compost helps improve aeration and runoff in heavier types like clay. Add a mulch layer to help retain moisture between watering sessions (while reducing overwatering). Rotate the placement of the crop seasonally to avoid rot.
Botrytis
Botrytis cinerea, or gray mold, is a common offender in dying basil. Brown spots and “fluffy” mold may appear. It often begins at the cut point made during harvesting the leaves, starting at the wound and spreading down the stem. Leaves drop, and plants die as it reaches the main stem.
To avoid infection at the harvest point, clip leaves and stems in dry conditions. Skip harvesting on rainy days or right before or after overhead irrigation. Water at the base of plants after a recent harvest, up to a day after, to reduce the chances of infection. Gray mold thrives in high humidity and with limited air circulation.
If caught in time, the herb may return to health by removing the impacted plant parts. Cut away and dispose of moldy portions, and see if new growth flushes with good spacing and watering protocols.
Pests
Pests don’t plague basil, but common visitors include Japanese beetles, slugs, and aphids, and they can cause dying foliage. It’s helpful to detect pests early to prevent them from transmitting diseases and impacting growing processes.
Japanese Beetles
Japanese beetles feed on leaves, causing them to skeletonize or turn yellow and drop.
In the active growing season, spray the plant with a strong stream of water to knock the insects off the stems. Do this in the morning so the leaves dry in the early sun.
You can also handpick the beetles off the stems and leaves and drop them into a bucket of soapy water. They usually stay for several weeks in the summer, depending on their activity in your area.
Aphids
Aphids are common sap-sucking insects that feed on a variety of plants. They cause stress by depleting resources, tissue damage, and are potential disease vectors. They also leave behind a sticky honeydew, leading to black, sooty mold.
With aphids and other soft-bodied insects like spider mites, whiteflies, and thrips, spraying the plant with a strong stream of water early in the day may deter them. A simple horticultural soap or oil rids the plant of larger infestations. Be sure to follow label directions, as these treatments affect pollinators and other beneficial insects.
Beneficial predatory insects like ladybugs and green lacewings help control populations. Grow a diversity of blooming plants with the herbs, even in pots, to draw beneficials and balance the garden system.
Slugs and Snails
Both slugs and snails may graze on the tender leaves, especially fresh shoots. They aren’t often a cause for mature basil plants dying, but they can contribute to decline. Hand-pick the pests early in the day or evening when they’re most active. If numbers increase, bait them with beer or soda traps by filling a shallow dish and placing it at soil level.
Diatomaceous earth scattered around the base of plants prevents them from reaching the stems to climb. The sharp texture of the powder harms soft-bodied, crawling organisms. Organic slug baits are effective, too.
