Tomatoes often have problems with cracking (sometimes called “growth cracks”), which are caused by pressure inside the fruit that is more than the skin can handle. Cracks are usually on the upper part of the fruit and can be concentric circles around the stem, or radiate out from the stem. We don’t know everything about tomato-cracking yet, but here is what we do know.
Tomato plants can crack when they absorb too much water too fast. They tend to have a root system that is very dense and fibrous and is quite efficient in picking up water. Having said that, there are various times when the size of the root system may be unbalanced with the amount of vegetative growth on top. Early in the season tomato roots may be somewhat undeveloped in relation to the plant size that is above ground resulting in blossom-end rot. And, as was discussed in my article three weeks ago, blossom-end rot is a dark-round, ugly formation located on the bottom of the developing fruit. This usually appears when the weather is hot and dry, and the plant cannot absorb sufficient amounts of calcium.
Later on, however, those same roots may be so efficient at absorbing water that they can actually provide too much water, especially when there is ample rainfall or heavy irrigation after a dry spell. A tomato’s interior grows quickly as it absorbs water from this abundant source, expanding too fast. The tomato skin cannot stretch to accommodate the extra fluid, causing internal pressure. Hence, cracking of the skin alleviates this pressure.
How can you prevent your tomatoes from cracking? One way is to maintain an even and consistent watering schedule throughout the growing season. Tomato plants need 1-3” water a week (including rain.) During dry spells, water tomatoes deeply so that subsequent rain won’t shock skins and lead to unnecessary cracking – use a drip hose or other irrigation system.
Mulching will also help because it moderates moisture levels in the soil. However, you can do everything right and still have problems with cracking in some years.
Still one more way to prevent cracking is to plant “crack-resistant” tomato varieties that have a more elastic skin (the more pliable the skin the more resistance to cracking). The old variety Jet Star has been the most crack resistant of any we have tested including the newer types. Unfortunately, Jet Star is an indeterminate variety that puts out rampant growth. Newer varieties with more controlled growth are often more attractive to gardeners. Mountain Spring, Mountain Pride, Mountain Fresh, Floralina and Sun Leaper are smaller-vined types that have shown good resistance to cracking.

Rip Winkel is the Horticulture agent in the Cottonwood District for K-State Research and Extension. Contact him by email at rwinkel@ksu.edu or call either 785-682-9430 or 620-793-1910.