How Much Sun Do Tomatoes Really Need?

Tomatoes love sunshine. They thrive in soil warmed by the summer sun and feed on the energy of the sun’s rays. Whether you plant tomatoes in containers or garden beds, it's important to site plants where they receive plenty of direct sun for optimal development and fruit production. But how much sun do tomatoes really need? And is there such a thing as too much sun?  

Understanding the impacts of sun exposure and associated heat set on tomato growth, flowering, and fruit production will help you determine how much sun tomatoes need and the best way to meet their needs in your garden.

Tomatoes Thrive in Full Sun

Sunlight plays an important role during all stages of tomato development, from root and vegetative growth to flowering and fruit production. Young plants focus their energy on establishing a healthy root system and developing strong stems and leaves. When plants receive too little light during this growth stage, they become leggy and produce thinner, weaker stems.  

Sunlight also powers flower and fruit development. When too little light reaches plants, they produce fewer flowers and subsequent fruits. Although tomato plants love warm temperatures, flowers and ripening fruits can be sensitive to very high heat. When temperatures soar, tomatoes often drop their flowers and established fruits may fail to ripen. These challenges can be managed through plant selection, planting location, and shading, as discussed below.

How Much Light Do Tomatoes Need?

Tomatoes need 6 to 8 hours of direct sunlight for the best production. This requirement is often described as full sun, a phrase that may sound somewhat vague, but has a clear definition. Full sun describes both the quantity and quality of sun exposure as 6 or more hours of direct sunlight per day. Direct sunlight is unfiltered and unobstructed by trees, buildings, shade sails, or other structures.  

When identifying the ideal location to plant tomatoes in the garden or set containers, pay attention to changes in sun exposure throughout the day as well as over the course of the growing season. The amount of sun reaching any given location can vary during the year as the angle of the sun changes. The intensity of the sun’s rays also varies throughout the day, with mid- to late-afternoon sun being the hottest. This can lead to production problems, particularly in very hot southern climates. Get to know your site by observing sun exposure and associated temperatures regularly.

Morning Vs. Afternoon Sun

To meet tomato’s high light requirements, plants will likely be exposed to both morning and afternoon sun. When you have an option, set plants in a location exposed to morning and early afternoon sun rather than late day sun. Morning sun helps manage foliar diseases in tomato plants by drying dew from the leaves. It is also less harsh than mid- to late-afternoon sunshine, which can be blistering. This is particularly important in the hottest regions of the Deep South, in Southwestern gardens, and Southern California. In these locations, provide filtered sun or light shade during the hottest parts of the day. 

Can Tomatoes Receive Too Much Sun?

In the hottest reaches of the South, intense afternoon sun can lead to blossom drop, sunscald, and poor fruit ripening. Blossom drop and poor ripening typically occur when daytime temperatures hit 85°F to 90°F and nights remain above 75°F. Shading can reduce temperatures in the plant canopy and help to reduce these problems. Likewise, some tomato varieties have a high heat tolerance and are less prone to blossom drop or problems with ripening. Consider planting 'Heatmaster', 'Brandywine', 'Celebrity', 'Porter Improved' cherry tomato, or another heat-tolerant variety.

Sunscald is more directly related to sun exposure. It appears as white or pale patches on fruits due to overexposure to direct sunlight. Healthy plants generally provide amply shade through leaf cover to protect developing fruits from intense sun exposure. However, if foliage is sparse due to heat stress, foliar disease, or other stresses, fruits are often exposed to direct sunlight and sunscald may occur. This problem can be prevented by providing afternoon shade. If you cannot locate plants where they are shaded by trees or other structures late in the day, consider using shade cloths to protect developing fruits. Cloths yielding 20-40% shade are ideal for tomatoes.