There is nothing more galling to a gardener than seeing a tomato you have loved and nurtured develop a split in the skin.
Tomato splitting its skin is one of the most common problems in gardens during summer, and the key is identifying which type of split you are dealing with!
Surprisingly enough, there are two different types of split tomato skins to deal with, that have differing causes and different urgency levels, with different treatments. Getting the right approach is key to saving your fruit.
Radial vs Concentric: The Split That Changes Everything
Concentric cracks form as a ring around the stem end of the fruit, with circular lines that are usually shallow and often scar over as the tomato ripens. This is largely cosmetic, and the tomato is still edible, thank goodness.
Concentric cracking occurs when a ripening tomato is damp due to either morning dew, mist or overhead watering, and the skin is hot from the sun. The rapid temperature contrast from hot skin due to direct sunlight to cold from the water causes the skin to expand and contract quickly, which causes the split.
Radial splits, however, are deep scars that are vertical from the stem end straight down the fruit and the tomato can almost look split in half. This has happened to my brandywine heirloom tomatoes due to a thunderstorm, and this sort of split isn’t just cosmetic. It forces you into a dilemma that you didn’t see coming.
It was just two summers ago when there was a potent heat wave in July, and I was carefully watering my tomatoes at the base every other day with a generous deep soak. One day, the heat turned to a thunderstorm, and down came 2 inches of rain in a few hours. The next morning, I’d say around 40% of my nearly ripe tomatoes had developed very deep cracks that ran vertically.
Here’s the botanical reason this happened: during the dry spell, the skin of the tomato lost elasticity due to the intense heat and lower water pressure, which meant the skin had tightened around the fruit. When the storm came, the roots suddenly absorbed water at a rate that was too quick for the tomato plant to regulate, which flooded the internal cells with water before the tomato skin had time to loosen to allow for the sudden internal expansion of tomato juice, and the skin just split along its weakest points.
Radial split rots very quickly and even attracts pests as they are open wounds, which means you have to confront the dilemma you weren’t expecting and make a decision on what to do here and now, rather than wait and see.
The Breaker Stage: Why Timing Is Everything
I wish someone had told me that tomato skin losses is elascticity as the fruit becomes ripe. A green tomato has skin that has lots of protopectin, which is a rigid structural compound that resists pressure well. As the tomato ripens in the sun, the protopectin degrades into sugars and pectins, and the skin becomes thinner and more porous, which means it cannot expand as quickly.
This is a point of vulnerability that growers call the breaker stage, which is when the tomato goes from green to a blush of colour at the blossom end of the fruit. This is the stage at which the fruit is actually capable of ripening off the vine, and the skin is starting to thin, which makes the risk of radial splitting from a sudden water influx very high.
The most important thing I learned from the Bradywine tomato incident: If you see that heavy rain is forecast and your tomatoes are at the breaker stage, then I would harvest them now and try to ripen them in your kitchen. A tomato that is at the breaker stage is going to ripen in around 3 to 5 days with the same flavour and texture but without the risk of splitting, whereas leaving the tomatoes on the vine to ripen through a significant rainstorm is too much of a gamble.
The Countertop Split Test
For us to undertsand why ripe tomatoes split and the unripe ones don’t, we can do an interesting kitchen experiment that makes the botany easier to understand in a way that changes how you think about watering.
Choose one solid green, unripe tomato and one ripe, red, soft tomato from your garden, ensuring neither has any cracks. Place them in a deep bowl or basin of water (lukewarm) and weigh them down gently with a small plate if they are floating, and keep both tomatoes completely submerged.
When 12 hours have passed, take a look at them as the difference in skin tension is already present. The green tomato has a rigid texture under water pressure, whereas the ripe tomato feels slightly swollen.
At the 24-hour point, remove both from the water, and you’ll usually see that the ripe tomato is going to have micro tears or full radial splits along the weakest points, whereas the green tomato is still going to look unblemished.
What’s happening here is osmotic pressure with the ripe tomato degraded due to its porous skin, which absorbs the water through the surface and stem joint far more readily than the green tomato, which increases the internal pressure, and the weak seems give way.
This illustrates my point about what’s happening in your garden when a dry spell is followed by a sudden downfall, bu rather in the garden, the water floods in through the roots at speed rather than slowly through the skin.
This experiment shows us why consistent soil moisture is key to preventing split tomatoes and why the breaker stage is the critical vulnerable window for tomatoes!
Prevention: Consistency Over Everything
Virtually all the radial splitting is due to moisture inconsistency, and it’s specifically the drought-followed-by-deluge cycle that causes an uncontrolled water uptake. So how do we prevent this? Well, all the strategies all take aim at the same root cause.
Consistent watering is key. What I prioritise is deep, slow water at the base of my tomatoes on a strict regular scheduale too prevent the levels of soil moisture from swinging from dry to soaking in a short period. What I’ve found works the best is drip irrigation, as it delivers the water at the root level in a steady way rather than the heavy periodic doses I was doing before with my watering can. If you don’t want to use drip irrigation then what I recommend is a long, slow soak every 2 days in dry weather, which I find works well.
Mulch is king. I love mulch, and I think it is chronically underrated, and I always use it now on my tomatoes. You can use straw, compost and wood chips, amongst other things, but I personally love homemade compost from my heap, which has a high concentration of leaf mould, which is excellent for holding moisture. This keeps the soil cool and evenly moist for longer periods, which prevents the drought-to-deluge cycle that causes problems.
Split-resistant tomato varieties! If you’re in a climate that is characterised by unpredictable rainfall, then it’s worth looking at some of the split-resistant varieties. Juliet, Legend and lots of the cherry varieties have thicker, more elastic skins that can tolerate sudden water spikes better than the larger heirloom tomatoes. My experience has taught me that brandywines are relatively vulnerable to splitting.
When to Harvest a Split Tomato Immediately
If they are concentric cracks that have scarred over with a rough, corky appearance then these are safe to leave on the vine to ripen whereas fresh concentric cracks on a ripe tomato should be harvested and eaten within a couple of days.
Radial splits, however, need to come off the vine the moment you see them, as the split is a wound that is vulnerable to infection, bacteria and pests during hot, humid conditions. Prune the tomato off and trim around the split, and you can still use the undamaged portion that day, but don’t leave it on the vine, as it won’t heal and could rot.
Dealing with splitting tomatoes and not sure whether to harvest or wait? Tell me which type of split, how ripe the fruit looks, and what the recent weather has been, I’ll help you decide.