Tomato Blossom End Rot and Drip Systems

Question from Walt:

Thanks for the very informative presentation at the Del Mar Garden Club. You did make a statement for which I need a little more info. You stated for tomatoes NOT to use a drip irrigation system. I have planted grafted tomatoes and would like to know what’s wrong with such a system. Many thanks in advance.

Answer from Pat:

The problem with drip systems for tomatoes is that drip systems do not blanket the ground with water, like natural rainfall would do. Other systems that blanket the soil with water include weeping or soaker hoses made from old tires, sprinkler systems, or even water applied by the gardener straight from the garden hose. Unlike drip, all these systems get soil evenly moist.

The water from a drip system, however, has a different action caused by the fact that water goes straight down with mighty little sideways movement, caused only by the soil’s wicking action, which differs from soil to soil. Most drip systems used by home gardeners create a buried shape of moist soil underground that is similar to the profile of an elongated or torpedo-shaped onion. The rest of the soil surrounding this buried “onion” of moist or wet soil might be bone dry. Also most drip systems are not left on long enough to water deeply enough for tomatoes. This situation does not harm most crops. They simply send their roots to the moisture and all is well, but tomatoes are different. If their roots are subjected to uneven moisture they are unable to take up calcium and this causes blossom end rot. Blossom end rot comes from a lack of calcium inside the tomato plant but there is actually loads of calcium in our soils and even more in our irrigation water.

One might think one would have less of a problem with blossom end rot when raising grafted tomatoes since they are grown on disease-resistant roots, which is why they are so great. However, thinking logically, I think you might have just as much problem since blossom end rot comes from a deficiency of calcium that the roots probably can’t solve. Unless you find a way to soak the soil deeply and in a blanket fashion with the drip system you most likely would still have a blossom-end rot problem in mid summer. What really works well for tomatoes is to water them once a week deeply or even once every week and a half (depending on your soil) and really soak the soil each time with gallons and gallons of water. However, this only works when tomatoes are raised in the ground, not in raised beds or in half barrels since these dry out too quickly so you have to water more often. The solution in containers is to water well each time to soak the entire container and thus make sure roots never dry out.

When growing tomatoes in the ground I used the water-basin system and each basin had a dam with a spillway on the side so water spilled over into the next one down the row. I would lay the hose down at one end of the row and let the water run slowly for half an hour or even an hour until it had filled all the water basins deeply with water. I did this once a week (in sandy soil) twice a week in summer. I got no blossom end rot this way. Deep and infrequent watering works even if there is dry soil away from the row. Studies have shown that tomatoes can send roots down as deep as 25 feet for water and then they never run dry.

I explained all this (briefly) at my talk, but you might not have heard or understood since I had so much information to get out there and so little time in which to do it. I recall mentioning that I once asked one of our Farm Advisors in San Diego how the commercial tomato growers manage not to have any problem with blossom end rot since all their tomatoes are grown on drip systems. The Farm Advisor said, “Oh Pat! What makes you think their tomatoes have no blossom end rot??!! Our farmers are fighting it all the time. It’s one of the worst problems to overcome. Many farmers feed tomatoes with Calcium nitrate hoping that will help but most of the time it doesn’t.” They lose a lot of their crop to blossom end rot.