Tomato plants require as much sun as you can give them, but high summer temperatures can burn the forming fruit and cause the plants to cease setting fruit. If you live in an area where the summers are extremely hot, you might want to consider giving your tomato plants a bit of shade, especially during the heat of the afternoon.
If you construct a simple frame made from 2-by-2 boards, PVC pipe or another inexpensive material, you can cover the top with shade cloth to protect your tomatoes against intense sunlight. Because tomatoes need eight to 10 hours of direct sun every day, your plants will not produce well if you give them too much shade. If possible, construct your shade shelter in such a way that it allows morning sun to reach your plant, while providing shade in the hot afternoon. Some tomato varieties, such as the Heatwave, Solar Set and Roma types, can tolerate strong sun better than other varieties.
This inexpensive material looks attractive in the garden and allows some sun to filter through it. Consider propping up privacy lattice at an angle on the west side of your tomato patch. You might need to build a simple frame to keep it in place, but the westward placement will protect your plants from the hot afternoon sun while allowing them to get the maximum number of hours of sun they need in the earlier, cooler part of the day.
If your summers are especially hot, you might need to provide your tomato plants with a bit of partial afternoon shade by planting them where a large tree or other plant will cast dappled shade on them. If the plants are located in an area where they will get full sun throughout the morning, they might grow big and strong and produce well if you give them some afternoon shade. Certain trees, such as black walnuts, are not good growing companions, so do a little research before you plant your tomatoes.