Why are the tomato fruit small, not deep red in color?

by JB
(Alpine, TX and Brewster, TX)

Q. My tomatoes are small, not a deep red, but rather when ripe, the color is more orange.

For many years, I lived in southeast Texas. Growing tomatoes has been no problem before. Now we moved to Alpine, TX (far west Texas, volcanic mountains arid land). Here, tomatoes do not set as easily. As plants age they gets purplish tent to the newer leaves, and stop blooming. Older leaves seem to roll inward. The top soil is at about 7.0 PH but 16” under is caliche (sedimentary rock, a hardened deposit of calcium carbonate). This caliche does not drain well, although the rest of the plot has good drainage.

I have supplemented the top soil with a good bit of peat moss and fertilized with 10-20-10 as have in the past. I water deeply once a week and I have applied additional fertilizer. We have grown several tomato varieties: Early Girl, Celebrity, Big Boy, Grape, and Better Boy -- all with the same results. I was wondering if the roots get down there could be what is causing the problem.

A. The lower caliche could certainly be a factor. However, you did not mention temperatures. Tomatoes struggle to reach their maximum size during an excessive heat wave, such as you often have in west Texas.

Heat stress forces a plant to increase transpiration (pumping water through its system) to survive, especially when the heat continues for prolonged periods. Heat stress not only slows down your plant’s progress in producing and in growing to a larger size, but it also makes your plant more vulnerable to diseases and pests. Further, heat prevents plants from blossoming.

As for color ... lycopene is a plant pigment which gives tomatoes their red color. The ideal temperature for lycopene development is 65-75º F. When temperatures rise above 75ºF and stay sustained, lycopene production is inhibited. Carotene, another pigment in tomatoes, produces yellow and orange. When higher temps and hot sun strike tomato tops, carotene (yellow) shines through while lycopene (red) is squelched.

But if temperatures have been cool, consider that your plants are struggling with phosphorus uptake. Purpling on leaves can be an indicator of phosphorus deficiency. Our best guess is that this is not a factor for you, since you've been using 10-20-10 (with the 20 in the middle representing a higher proportion of phosphorus.)

You can counter the size and ripening issues a couple of ways. Consider growing tomatoes in raised beds. Raised beds will allow you to deepen the tomato plot even further (as you have with your regular garden plot) with good topsoil, compost, and lots of organic matter.

Another step to take is to determine the best planting date for your new area and adjust your planting schedule accordingly. By setting out plants earlier in the spring, you can help them hit their high production time before the truly brutal heat sets in. You may also want to consider trying a couple of other tomato varieties for hot, arid climates. And even try a second season of tomatoes in the fall that will reach maturity during the cool autumn weather.

Good luck and happy gardening!
Your friends at Tomato Dirt