Tomatoes A–Z

The pollen-producing parts of a tomato flower. Tomatoes are self-pollinating — pollen falls from the anthers onto the stigma within the same flower. You can gently shake the plant or use a vibrating tool to improve fruit set, especially indoors or in low-wind conditions.

Blossom End Rot: a dark, sunken, leathery patch that forms on the bottom of developing fruit. Not a disease and not contagious — caused by calcium failing to reach the fruit fast enough, usually because of inconsistent watering. The plant has calcium; it just can't deliver it quickly enough during rapid fruit growth.

When tomatoes split open, either radially (lines running from stem to blossom end) or concentrically (rings around the middle). Almost always caused by irregular watering — especially a heavy rain or deep watering after a dry period. The fruit absorbs water faster than the skin can expand.

A tomato variety that grows to a genetically fixed height, sets all its fruit within a short window, and then stops. Determinates are compact, don't need heavy pruning, and ripen most of their crop at once — making them ideal for canning, sauce-making, or anyone who wants a predictable harvest. Roma and San Marzano are classic determinates.

One of the most common tomato diseases. Caused by Alternaria solani — a fungus that creates dark brown spots with concentric rings (like a target) on lower leaves. Spreads upward as the season progresses. Not usually fatal but weakens the plant and reduces yield if left unchecked. Most active in warm, humid conditions.

A fungal disease caused by Fusarium oxysporum that lives in the soil and blocks the plant's water-conducting vessels. Causes yellowing, browning, and wilting that starts on one side of the plant and progresses upward. No cure once infected — prevention means choosing resistant varieties (look for "F" on seed packets) and rotating crops each season.

Joining a desired tomato variety (the scion) to a disease-resistant, vigorous rootstock. The result is a plant with the flavor and fruit of the top variety and the root system of the bottom. Grafted tomatoes are more expensive but significantly outperform non-grafted plants in disease pressure, yield, and vigor. Standard practice in commercial greenhouse growing.

An open-pollinated tomato variety that has been passed down through generations — generally defined as 50 or more years old. Heirlooms are known for flavor complexity that commercial hybrids can't match, as well as visual diversity (colors, shapes, sizes) that has been largely bred out of supermarket tomatoes. All heirlooms are open-pollinated; not all open-pollinated varieties are heirlooms.

A tomato plant that keeps growing, flowering, and producing fruit continuously until frost. Most heirloom varieties are indeterminate. They require staking or caging and benefit from pruning to manage size and airflow. The tradeoff for all that growth: fruit all season long, often with exceptional flavor. Brandywine, Cherokee Purple, and most cherry tomatoes are indeterminate.

The natural shedding of blossoms or very small fruit early in the season. Often alarming to first-time growers, but usually normal. Caused by temperature extremes (too hot or too cold overnight), lack of pollination, or the plant redirecting energy. If blossoms drop consistently, check nighttime temps and consider hand-pollinating by gently shaking flowers.

Removing a sucker at the point where it meets the main stem — the knuckle. Leaving a small stub (rather than cutting flush) allows the wound to heal cleanly without creating an entry point for disease. Best done when suckers are small (under 2 inches). Larger suckers should be cut with clean, sterilized pruning shears.

Caused by Phytophthora infestans — the same pathogen responsible for the Irish Potato Famine. Creates dark, water-soaked lesions on leaves, stems, and fruit that spread with alarming speed in cool, wet conditions. One of the most serious threats a tomato grower can face. Unlike early blight, late blight can kill a plant in days. Remove and destroy infected plants immediately — do not compost.

Applying a 2–3 inch layer of organic material (straw, wood chips, compost, shredded leaves) around the base of plants. Mulch does several jobs at once: retains soil moisture, regulates soil temperature, suppresses weeds, and prevents soil splash — which is how many diseases spread from soil to lower leaves. One of the highest-return habits a tomato grower can build.

Microscopic roundworms that live in soil. Root-knot nematodes are among the most damaging tomato pests — they invade roots and create swollen galls that block water and nutrient uptake. On seed packets, resistance to root-knot nematodes is indicated by the letter "N." Beneficial nematodes, sold as a garden product, can help control soil-dwelling pests like grubs and fungus gnat larvae.

A variety pollinated by natural means — insects, wind, or gravity — that produces seeds which grow true to the parent plant. This means you can save seeds from an open-pollinated tomato, plant them next year, and get the same variety. All heirloom tomatoes are open-pollinated. Hybrids are not — their seeds produce unpredictable results.

Selectively removing plant material — suckers, lower leaves, or the growing tip — to improve airflow, direct energy to fruit, and manage plant size. Indeterminate heirlooms benefit significantly from regular pruning. The goal isn't to minimize the plant but to keep it open, healthy, and focused. Unpruned plants produce more total fruit; pruned plants produce fewer, larger, often higher-quality fruit.

Isolating new plants, seeds, or soil before introducing them to your garden. A basic practice for preventing the spread of disease and pests. New transplants from a nursery should ideally be kept separate for a few days and inspected before planting. Soil from unknown sources can carry fusarium, nematodes, or weed seeds — quarantine before mixing.

The lower portion of a grafted tomato — the root system and bottom stem selected specifically for vigor and disease resistance rather than fruit quality. Common rootstock varieties are bred to resist soilborne diseases like fusarium, verticillium, and nematodes. The rootstock does the underground work; the scion (top) delivers the flavor.

A side shoot that grows in the axil — the V-shaped junction between the main stem and a branch. Left alone, suckers become full stems and the plant turns into a sprawling bush. Removed when small, they redirect the plant's energy into existing fruit. Whether to remove them is one of the most debated questions in home tomato growing. The answer depends on your space, your goals, and your variety.

Cutting off the growing tip of an indeterminate plant — usually 4 to 6 weeks before first expected frost. Topping stops the plant from producing new flowers (which won't have time to mature) and redirects all remaining energy to ripening existing fruit. One of the most useful end-of-season techniques for getting the last tomatoes off the vine before cold sets in.

A geographic classification system based on average annual minimum temperatures. Used to determine which plants will survive winter in a given location. For tomatoes — which are warm-season annuals — the zone matters less than the frost dates. Knowing your last spring frost date and first fall frost date tells you exactly when to plant and when to expect your season to end.

A fungal disease caused by Verticillium dahliae that lives in the soil and invades plant roots. Symptoms include yellowing and wilting of lower leaves, often with a V-shaped yellow lesion at the leaf margin. Progresses slowly compared to fusarium. No cure; management through resistant varieties (look for "V" on seed packets), crop rotation, and avoiding infected soil.

When a tomato plant loses its structural rigidity and droops. Wilting has many causes — and most of them are reversible. Afternoon wilt on a hot day is normal; if the plant recovers by morning, it's just heat stress. Persistent morning wilt points to something more serious: underwatering, root damage, compacted soil, or a soilborne disease like fusarium or verticillium.

The genus of bacteria responsible for Bacterial Spot — one of the most damaging tomato diseases in warm, humid climates. Xanthomonas vesicatoria enters through leaf pores and wounds, creating dark water-soaked spots on leaves and raised, scabby lesions on fruit. Spreads rapidly via rain splash and overhead watering. Copper-based sprays slow the spread; prevention is better than treatment.

Yellow leaves are one of the most common things tomato growers worry about — and one of the most commonly misdiagnosed. Lower leaves yellowing as the plant matures is completely normal. Yellowing that starts at leaf tips suggests overwatering or poor drainage. Uniform yellowing of new growth usually means nitrogen deficiency. Mottled yellow patterns often signal a virus. Location and pattern matter more than color alone.

A trace mineral essential for enzyme function, cell division, and plant growth. Zinc deficiency in tomatoes causes mottled, yellowed young leaves with shortened internodes — the spaces between leaves become compressed, giving the plant a stunted, bunched appearance. Usually addressed through a balanced fertilizer or a targeted zinc spray. More common in high-pH soils where zinc becomes less available to roots.