Tomatillo (Physalis philadelphica) is a warm-season annual in the nightshade family, native to Mexico and cultivated since pre-Columbian times. It produces small round fruit, green to purple at maturity, enclosed in a papery husk. It is a staple of Mexican cooking, most prominently in salsa verde, and is used both raw and cooked.
Though technically a perennial, tomatillo is grown as an annual everywhere outside frost-free climates. A critical growing detail: the species is largely self-incompatible. A single plant produces little to no fruit. Always plant at least two individuals — ideally from different seed sources — for reliable cross-pollination. Plants sprawl aggressively and benefit from caging or staking at transplant time. Harvest when the husk splits and the fruit fills it out completely; husked fruit feels slightly sticky.
The fruit contains physalins, a group of withanolides found across Physalis species. Laboratory studies have documented antimicrobial and anti-inflammatory activity. In traditional Mesoamerican medicine, Physalis species have been used for fever reduction and as a diuretic.
Early Blight
Dark brown spots with concentric rings on older lower leaves, surrounded by yellowing. Leaves drop, exposing fruit to sunscald.
Remove affected leaves, mulch to block soil splash, water at the base, and rotate crops. Apply copper or chlorothalonil fungicide if it spreads.
Late Blight
Dark, water-soaked lesions expand rapidly on leaves and stems, often with a pale yellow border. White mold forms on leaf undersides during humid conditions. Infected tubers show reddish-brown dry rot just beneath the skin that can extend deep into the flesh.
Remove and bag all affected plant material immediately — do not compost. Apply copper-based fungicide preventively when overnight temperatures drop below 65°F with sustained leaf wetness. Avoid overhead irrigation. Use certified disease-free seed potatoes and plant resistant varieties. Do not save tubers from infected plants for replanting.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Mosaic virus
Yellowing, mottled, or distorted leaves. No cure — spread by aphids.
Remove and destroy infected plants. Control aphid populations to prevent spread. Do not propagate from infected tubers.
Root-Knot Nematode
Swollen galls on roots, poor vigor, wilting in heat, and reduced fruiting. Containers and sandy soils are more prone.
Use clean potting mix in containers. Avoid replanting in infested soil. Maintain plant vigor with mulch and steady watering. Solarize affected garden soil.
Damping Off
Seedlings collapse at the soil line with thin, water-soaked stems; seeds may fail to emerge or rot before sprouting.
Sow in well-draining mix, avoid overwatering, and ensure good airflow. Remove affected seedlings and let the surface dry between waterings.
Fusarium wilt
Sudden wilting, brown streaks in stems, yellowing leaves. Affects sweet basil varieties most.
No cure. Remove and destroy plants. Do not replant in the same spot for 3+ years. Choose resistant varieties.