Kohlrabi Splitting: Why Does It Happen and What Can You Do?

Kohlrabi is one of those vegetables that’s supposedly easy to grow, and fast-maturing if you’re selecting early cultivars. But, for some reason, I always run into problems when trying to grow it to a decent size. I’m sure it has a lot to do with my climate – lingering winters and short rainy springs – which cause my kohlrabi plants to often split.

Some kohlrabi tubers I’ve grown either split early in the season (and continue to grow) or near harvest time when I’m still waiting for them to plump up. So why does this happen? Why is kohlrabi sometimes splitting and is there anything we can do about it?

Kohlrabi tubers split because of sudden growth, often following a rainy period. Extreme water fluctuations and too much fertilizer can encourage splitting, as well as harvesting the kohlrabi too late in the season. Early maturing kohlrabi cultivars are more prone to cracking than late varieties.

Now, a few cracked kohlrabi, root vegetables, tomatoes or fruit, never hurt anyone, especially a home gardener. Cracked kohlrabi is mostly an issue with commercial growers because blemished kohlrabis are harder to sell. So if you’re frustrated with your kohlrabi plants either not growing large enough or cracking when they’re still small, read on and you may learn a thing or two.

How does cracking manifest in kohlrabi tubers

When kohlrabi tubers split, it happens because their outer skin is not elastic enough to adjust to the flesh which is growing rapidly. Much like with stretchmarks in humans – get too fat, too fast, and your skin has no other option but to break.

Cracks usually occur on the top part of the kohlrabi tuber and rarely go all the way down to the base. They can be horizontal or vertical, big or small. Now the interesting part is that there are two types of cracks:

• Some kohlrabi plants split when the tubers are small, even less than an inch in diameter. This can happen following heavy rain, or extreme heat, or both. What’s interesting is that this early crack heals, becomes smooth and rounded, and opens up as the kohlrabi continues to grow. The stem’s flesh is no longer exposed and develops some sort of “crust” on top of it.

• The second kind of crack is late in the season. This is when you’ve left kohlrabi in the ground too long and they’re becoming woody. Rainfall and heat waves will lead to kohlrabi cracking, and fresh cracks will look sharp and expose white flesh. I’ve often seen ants invading these fresh cracks for some reason, as well as slugs. Left for too long, the cracks can get mushy and even rot.

With late splitting, this often happened to me because I left kohlrabi to swell up a little longer, thinking I’d get bigger bulbs. Unfortunately, some cultivars don’t have the potential of growing more than 3 inches in diameter – which is a waste, if you ask me, for all that space that kohlrabi’s foliage takes up in the garden.

If you’re dealing with fresh white cracks, harvest your kohlrabi immediately, before ants and other insects decide to feast on them.

Why do kohlrabi bulbs split

We’ve mentioned extreme water variations – excessive rain following drought – and that’s the main reason for cracking in kohlrabi, as well as cabbage, its close cousin. But aside from the rain, there are a few other factors to take into account:

• Some kohlrabi cultivars are simply more prone to splitting. For example, Express Forcer is notorious for its tendency to cracking, because it grows so fast – but its advantage is that it reaches maturity in only 42 days since direct sowing.
• Fall kohlrabi is reportedly more prone to splitting than spring kohlrabi.
• Purple kohlrabi – in my personal experience – split more than white kohlrabi, but some gardeners may have the opposite experience. I haven’t had much luck with Purple Vienna – an early and delicious purple kohlrabi.
• Over fertilizing, particularly soils that are too rich in nitrogen, encourage rapid plant growth and this may lead to splitting, especially when combined with an early kohlrabi cultivar.
• Old kohlrabi plants will crack when left for too long in the ground, and also become woody and unusable.