How Much Sun Do Tomatoes Need?

Sun on Tomatoes

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Every gardener growing tomatoes waits for that first juicy, fresh, off- the-vine bite. When the wait seems to go on forever and fruits stay green for weeks, you might think they aren't getting enough sun but that's probably not the case.

Sunlight functions in two ways in the garden. It provides the energy plants need to take up and process nutrients. It also raises soil and air temperatures. Tomato plants need lots of sun, a minimum of six hours, through all growth stages. When your tomatoes refuse to turn, they could be getting too much sun.

Here's what to know about how much sun tomatoes need, and our best advice on how to get them the light they need to give you the growth you want.

Light Requirements for Tomatoes

Finding the perfect place to plant tomatoes takes a little planning. That's because light exposure plays a major role through all stages of plant growth, so tomatoes will have different requirements for light depending on the growth stage.

In the early growth stages, poor light and high temperatures can decrease flower and fruit production and increase vulnerability to fungal and leaf spot diseases and insect infestation. Later, not enough light produces straggly weak vines and small, poor-quality fruits. And during fruit development, too much sun leads to a poor harvest with fruits vulnerable to sunscald, cracking, and uneven ripening.

Vegetative Stage

During the first 30 to 45 days after transplant, tomato plants grow vines and leaves. This is called the vegetative stage and may be a little shorter or longer depending on variety. Vines grow rapidly and use a lot of nutrients. Since nutrients are delivered through photosynthesis which is dependent on energy from light, a minimum six hours of bright, direct sun is needed during early growth.

Flower/Early Fruit Stage

Between 30 and 45 days you should begin to see small yellow flowers open on your plants. In this stage light energy supports flowering and fruit set. Small fruits start to form between 70 and 100 days depending on variety. Six hours of light is adequate and eight hours can boost fruit production. Excess heat begins to enter the equation and temperatures above 85 to 90 degrees can reduce flower production and fruit development.

Ripening Stage

Temperature becomes more important during the ripening phase about 30 days after fruit appears. Lycopene and carotene are pigments that give tomatoes their red color. Ideal temperatures for pigment to develop is 70 to 75 degrees F. When temperatures exceed 85 to 90 degrees F., pigment production is reduced and may even stop.

Grown and cared for correctly, foliage shades fruits which takes heat out of direct sunlight for more uniform ripening. Six to eight hours is still needed to maintain healthy plants, especially with indeterminate varieties that produce fruit all season long.

Morning vs. Afternoon Light

How many hours of sun your garden receives depends on where you live and how your garden is oriented. Geography directly impacts both light availability and temperature. Elevation can reduce daylight hours and, along with rivers, lakes and oceans, affect weather patterns and temperature fluctuations. Factors like cloud cover and rain also play a role.

Tomato plants need and benefit from both morning and afternoon light.

Why Tomatoes Need Morning Light

Around mid-morning the sun is high enough overhead, in an open east to west orientation, to shine directly on the garden. At noon it reaches its zenith, the highest point during daylight hours. This is when it is strongest, producing the greatest amount of energy.

Morning light is important because it dries dew, decreases nutrient loss through evaporation and initiates photosynthesis. As the sun moves toward the zenith, more energy is created to accelerate growth. Locations that receive first available light start the daily growth cycle with quality exposure.

Why Tomatoes Need Afternoon Light

Sunlight continues to fuel photosynthesis throughout daylight hours, so afternoon exposure extends the daily energy and growth cycle, giving tomatoes the sunlight quantity they need. For growers in regions with high average daily temperatures, afternoon heat levels, which generally peak between 2pm and 4pm, present challenges. Extended periods above 85 degrees cause flowers to fall or fail to produce fruit and reduce pigment needed for ripening. Southern tomato growers have the advantage of longer daylight hours and extended growing seasons, but need to factor in higher temperatures and humidity resulting from greater rainfall amounts.

Ways to Provide the Best Light to Tomatoes

In spite of weather variables, there are ways to best use the sun's energy to support and improve your tomato crop.

  • Plant tomato varieties that grow well in your specific growing zone and climate.
  • Mulch to lower soil temperature and improve moisture retention.
  • Orient your plants in an east to west direction to access first sunlight in the morning and throughout the day.
  • Consider geographic features that reduce light availability or create microclimates.
  • Avoid pruning or removing leaves during fruit formation and ripening.
  • Plant corn or pole beans on the western side for protection from hot afternoon sun.
  • Leave adequate space between plants for good air circulation.
  • Consider using white shade cloth which reduces heat but doesn't affect light quality.
  • Harvest fruit early as soon as it shows color and keep in a shaded area to finish ripening.
  • Can tomatoes get too much sun?

    Yes, tomatoes can get too much sun. Too much bright direct sunlight on plants can raise temperatures too high for ripening and lead to cracking and sunscald. It can also create problems caused by high humidity or dry soil.

  • Do tomatoes prefer morning or afternoon sun?

    Tomatoes need both morning and afternoon sun and at least six hours of sun a day. Morning sun is important because it starts photosynthesis. Afternoon sun maintains energy needed for healthy growth.

  • Is four hours of sun enough for tomatoes?

    Tomatoes need a minimum of six hours of bright, direct sun. Anything less yields weak or stunted vines with poor fruit development and reduced harvests.

Article Sources
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  2. Shade Cloth: Need, Purpose and Options, Local Food Connect