This is a conundrum I'm trying to figure out.
Granny ran a brief test on the flavor of tomatoes in relation to watering habits. She found that holding out on watering until your plants began to wilt a bit gave her better tasting tomatoes. This is legitimate, I've heard the same from other gardeners.
My system makes this a bit tricky since I have a shallow, very well-draining bed with pumpkins and beans in it on the same water line as the tomatoes. That drip line runs for 40 minutes a day twice daily, morning and night. The line is soaker hose through the two big beds and ends in a round sprinkler in the center of the pumpkin bed. The sprinkler has a shutoff valve so I have it turned down to a steady 2 ft. diameter circle; otherwise it would spray everything 4 feet high and 4 feet around it. Meanwhile the shutoff at that end allows the rest of the hose enough pressure to seep nice and slowly into the larger beds.
So I am wondering just how much water they are actually getting. I know the top soil of the tomato beds, up to the depth of my pinky, is bone dry by the afternoon. If I don't water in the evening on hot days the pumpkin leaves wilt badly.
My tomatoes were definitely mealy and somewhat bland last year though, so I want to give this a shot and try to find a comfortable balance in watering.
I'm also curious what sort of difference the reduced watering makes over the life of the plants. During their initial growth, when their chemicals are giving the command "GROW", it seems like more water should be fine. It is the delivery system for most of the nutrients the plant needs. So I'm thinking that if you pinch back flowers (and suckers of course) to allow the plant to put more energy into growth; then begin tapering off the water as flowering begins. Tapering off the water at this point (when plant chemicals are giving the command "REPRODUCE") would cause the plant roots to reach more for water, and conserve its nutrients for seed production (e.g. tomato production). So plant growth should slow, but fruit growth should improve.
I'm only guessing of course, but based on plant biology it seems like this would work.
Now the downside to this is BER. BER, or blossom end rot, is a tomato disease that is attributed to calcium deficiency. This doesn't necessarily mean that your soil doesn't have enough calcium though. Calcium is often present in adequate amounts but not accessible to the plants because of lack of water (remember, water is a nutrient delivery system; like our stomach acid it dissolves the nutrients into particles that the roots can absorb). So there has to be a sweet spot between mealy tomatoes, delicious tomatoes, and BER; and finding that sweet spot in watering can be a challenge.
-Every garden is different! If your aunt waters for 20 mins. once a week, it doesn't necessarily mean you should too. Differences in localized temperature, sun exposure, drainage, depth of soil, etc. mean that each garden should be treated as an individual space.
-Pots lose moisture faster than raised beds, raised beds lose moisture faster than in ground beds. If you have a potted tomato plant it will need to be watered more often than one planted into the ground.
-Water deeply. Many people water their gardens by hand, spraying the base of each plant until it is wet, then moving to the next plant. This is fairly shallow watering, much of the water evaporates off the top layer of soil, and the rest rarely gets into the soil far enough to encourage deep root growth. Instead it stays in the top few inches of soil, causing plants to form more roots near the top of the soil. These roots will be exposed to greater changes in temperature and moisture and will not grow as healthy of a plant. If you water by hand turn the hose to a trickle and let it sit at the base of each plant for several minutes, giving it time to soak deep into the soil before moving it. A better system (and far less time consuming) for deep watering is to run a soaker hose, drip line, or even a low sprinkler that won't wet the leaves.
-Watch for wilting at the end of each day, if the plants begin to wilt it is an indicator that they are water stressed and need a drink.
-Watch for signs of BER, the blossom end of developing tomatoes will look shriveled, brown, and somewhat wet. If you start to see signs of BER remove the damaged tomatoes to encourage new fruit production and increase your watering a bit. If it continues, have your soil tested for calcium deficiency before adding calcium to it.
-BER is particularly damaging in the southern and southeastern states where temperatures reach triple digits regularly and shallowly watered tomato plants can be starved for moisture in an afternoon. Watch for the signs, water deeply, and water more often if your soil is sandy or drains very quickly.
-Another good way to get deep root growth and healthier tomatoes is to plant them deeply. Pinching off the lower leaves and planting them into the soil up to the higher leaves lets the plants grow new roots all along the stem that is buried. This method only works with tomatoes though, so don't try it with other garden vegetables. If your soil isn't deep enough for this you can plant them horizontally into a trough, and bury the stem up to the upper leaves. Roots will grow along the buried stem, and the sunlight will eventually cause the plant top to grow upwards.
I hope these tips are helpful... Now I have to go adjust my watering system and cross my fingers. ;)