A dark, sunken patch at the bottom of a tomato, zucchini, or summer squash can be discouraging, especially when the plant looks healthy elsewhere. This disorder is called blossom end rot, and it often appears during periods of rapid fruit growth, hot weather, or uneven watering.
The problem begins when developing fruit receives too little calcium through the plant’s water-conducting tissues. The soil may contain adequate calcium, yet stressed roots cannot consistently move it where it is needed. That is why regular moisture, healthy roots, and careful fertilization are central to prevention.
Gardeners in LaPorte and surrounding areas can find seasonal growing supplies and local greenhouse support through the Angelo Bernacchi greenhouse, where thoughtful plant care begins with selecting vigorous plants and appropriate products.
Blossom end rot usually starts as a small, pale, water-soaked spot on the blossom end of the fruit—the end opposite the stem. The mark soon turns tan, brown, or black and becomes leathery or sunken. On tomatoes, the damaged area may remain relatively small or expand across much of the lower fruit.
Squash may develop a similar dark patch, although the fruit can soften or stop growing quickly. Blossom end rot is physiological rather than contagious, so it does not spread from plant to plant like a fungal disease. Remove severely affected fruit so the plant can direct energy toward new growth, but do not discard the entire plant.
Consistent watering is the most effective way to reduce calcium-related fruit damage. Allowing plants to dry out and then soaking them heavily creates fluctuations in water uptake. These swings are common when summer temperatures rise, during vacations, or when shallow-rooted plants compete with nearby vegetation.
Water deeply at the base of each plant when the upper inch of soil begins to dry. A soaker hose or drip line delivers moisture to the root zone while keeping foliage dry. Apply two to three inches of organic mulch, such as straw, shredded leaves, or finished compost, around plants. Keep mulch a few inches away from the stem to reduce rot and pest problems.
Healthy roots are essential for moving calcium and water into developing fruit. Before planting, loosen compacted soil and mix in mature compost to improve drainage, moisture retention, and root growth. Containers should have drainage holes and a high-quality potting mix rather than ordinary garden soil, which can become dense and waterlogged.
Test garden soil when possible instead of adding amendments based on symptoms alone. If a soil test shows low calcium or an unsuitable pH, apply the recommended amendment according to the test results. Adding large amounts of lime, gypsum, or crushed eggshells without testing may create nutrient imbalances and will not provide an immediate cure for fruit already affected.
Excessive nitrogen can produce lush leaves and stems while delaying balanced fruit development. Fast-growing plants may then struggle to supply calcium to fruit during periods of heat or drought. Choose a fertilizer formulated for vegetables, and follow the package rate rather than assuming that more feed will produce a larger harvest.
Avoid disturbing roots after flowering begins, since damaged roots absorb water less efficiently. When transplanting tomatoes, harden seedlings gradually and plant them in a location with full sun and good air circulation. Squash should have enough space for its broad foliage and extensive roots, reducing competition for moisture and nutrients.
| Growing condition | What it can cause | Preventive response |
|---|---|---|
| Soil repeatedly dries out | Interrupted calcium movement and stressed roots | Water deeply and maintain mulch |
| Heavy watering after drought | Rapid changes in plant water uptake | Follow a regular watering schedule |
| Compacted or poorly drained soil | Weak or damaged roots | Improve soil structure and drainage |
| Excess nitrogen | Excess foliage and uneven fruit growth | Use a balanced vegetable fertilizer |
| Root disturbance | Reduced ability to absorb moisture | Cultivate carefully around established plants |
| Unusual soil pH or low calcium | Poor nutrient availability | Use a soil test before amending |
High temperatures increase evaporation from soil and leaves, so plants may need closer monitoring during heat waves. Check containers and raised beds daily because they dry faster than in-ground beds. Water early in the morning, when less moisture is lost to evaporation and roots have time to absorb it before afternoon heat.
A temporary shade cloth can protect plants during extreme heat, especially in containers or exposed patios. Do not rely on frequent, light sprinkling because it encourages shallow roots. Deep, even irrigation supports a more stable root system and helps tomatoes and squash continue developing fruit.
A strong start makes fruiting plants more resilient. Choose healthy transplants with sturdy stems, dark green leaves, and well-developed roots. Avoid plants that are severely root-bound, wilted, or already showing damaged fruit. Gradually acclimate greenhouse-grown seedlings to outdoor conditions before planting them permanently.
Rotate tomato and squash planting areas when space allows, and remove spent plants at the end of the season. Good sanitation will not directly correct blossom end rot, but it lowers pressure from diseases and pests that can further stress plants. Harvest zucchini and summer squash regularly as they reach usable size, which encourages continued production without placing unnecessary demand on the plant.
Use the following routine throughout the growing season:
If new fruit develops normally after moisture and root care improve, the plants are recovering. Existing damaged areas will not heal, but later fruit can remain healthy when growing conditions become more consistent.
Make blossom end rot prevention part of your regular garden routine: prepare the soil, monitor moisture, protect roots, and feed with restraint. For dependable vegetable-growing supplies and seasonal guidance, connect with Angelo Bernacchi Greenhouse and plan your next tomato and squash planting with confidence.