Radishes are an early spring treat in the vegetable garden, usually ready to harvest after just four weeks, but in recent years we’ve noticed that this once simple crop has become much more prone to holes, hollowing and woody roots.
If you’re asking the same questions we are – why are radishes hollow, why are my radishes split… then it’s probably time to look at some of the great radish growing hacks we’ve found to prevent split or hollow radishes next time you sow them.
How to grow radishes
You can sow radishes from early spring to mid-fall as they are incredibly quick to develop their sweet, spicy, roots. The downside of this long growing season is that radishes are often a great early treat for common pests, and the fluctuating temperatures and rain can cause problems too.
Ideally, radishes need loose compost or well-fertilized soil to grow. They need space to expand, and should always be sown at least half an inch deep to avoid ‘popping’ radishes, where the entire radish bulb begins to form above ground.
As you can tell from the crisp, juicy roots that form at the base of dense leaf clusters, radishes need a LOT of water, ideally with a generous watering twice a week as a minimum.
This used to be easy as spring weather was far more reliable but thanks to climate change (the ever-present enemy of vegetable growers) we have to rely more on watering cans to grow early spring radishes.
Radish growing problems
Throughout this article we’ll dig deep into not just radish problems but what causes them, including hollow radishes, split radishes, and spongy radishes. Some of the most common radish growing problems are:
- Split radishes
- Spongy radishes
- Hollow radishes
- Radishes with excess leaves
- Woody radishes
Why do radishes split?
- Late harvesting
- Irregular watering
Radishes instinctively take up any water they can get. That means that dry radishes with tight skins that have started to harden will fill up until their skins split.
There is no problem at all eating split radishes, and their flavor can be pretty intense too. Split radishes are most often caused by uneven watering, but can also be the result of late harvests.
Why are my radishes spongy?
- Late harvesting
Spongy radishes, also referred to as pithy radishes, are a result of late harvests. At least that’s what we used to believe. Today, harvesting times for radishes are very different, and it’s less about time and more about watching for signs.
If you harvest radishes early, as soon as their shoulders show above the soil, you’ll have small crisp root vegetables that are perfect for salads. The temptation is to leave them mature, but the reality is that hot springs coupled with unpredictable rainfall can cause radishes to develop faster.
We used to expect a radish harvest around four weeks after sowing, but it’s really important to check them as often as possible after three weeks. That way you’ll avoid pithy radishes, but potentially have a smaller crop.
Why are my radishes hollow?
- Dry soil
- Excess drainage
- Old compost
One cause of hollow radishes is dry soil, so make sure to mix plenty of compost through your bed before sowing to help moisture retention. No matter how well you water vegetable beds, they can dry out if their compost has been exhausted the previous year.
The ideal radish is a crisp, spicy, root ball with tight red skin around a bright white interior. Last year, our radishes were about as far from that as possible. We had hollow radishes which were soft and beginning to wrinkle.
Why do radishes grow excess leaves?
- Excess nitrogen
- Damp soil
If you prefer radish roots to radish leaves, seeing masses of leaves above the soil, and the small or withered roots below ground can be pretty frustrating. High nitrogen leaves can cause this sudden flush of leaves, but so can damp compost.
Radish is a member of the brassica family – closely related to cabbages and mustard which is where they get their earthy spice from. That means that their leaves are edible too, and make a brilliant salad crop. So if you’ve got leafy radishes that aren’t forming bulbs below, make the most of it and enjoy the bonus salad leaves.
Why are my radishes woody?
- Late harvest
Radishes that have gone past their ideal harvest time turn woody. It’s probably the most common problem when harvesting radishes, as we always think bigger is better. However, radishes not only taste better smaller but suffer from fewer problems as a result of early harvesting.
To avoid woody radishes, harvest them as soon as you see their shoulders above the soil. One hack to help delay radish harvests is to hill them up when their foliage first appears. This reduces light levels to the roots creating more whites on the root, thus reducing the chances of tough woody tops.
How to prevent radish problems through better radish care
As we’ve discussed above, there are very common care problems that cause radishes to grow hollow, woody, pithy or even split. Below we’ll look at the best ways to care for radishes to avoid these common growing problems.
General reasons for pithy radishes:
- Soil nutrients
- Soil drainage
- Watering (or lack of watering)
- Late harvesting
- Shallow sowing
Pests like flea beetle and slugs are a big problem for radish, but other culprits that gardeners tend to ignore can often be a big problem for radish, like ants or woodlice.
Planting marigolds around radishes is a great way to keep insects away from your crop. Remember, radish is a brassica, so anything that enjoys cabbages will target radish just as often, and marigolds are one of the most reliable companion plants for this vegetable family.
One multifaceted approach is to improve the soil structure. Radishes are true goldilocks plants – not too hot, not too cold, not too wet, and not too dry. Good compost not only helps reduce pest damage but gives proper nutrition and drainage, which makes watering radishes more straightforward.
And the last culprit? Sowing radishes right in the first place! Radishes that are sown too close to the surface will develop above ground, risking pest damage, and woody roots. Sowing small seeds is always tricky, but next time, try sowing radish in half-inch deep drills.
The best radish varieties to grow to avoid problems
Some radish varieties, like the French Breakfast Radish or Hailstone Radish, are more susceptible to root damage than others, so try sowing the best radish varieties to avoid hollow roots:
- Bartender Mammoth Radish
- Golden Helios Radish
- Red King Radish
- Royal Purple Radish
Two late harvesting varieties of radish, Bartender Mammoth and Golden Helios, are particularly useful to grow in unpredictable climates thanks to their longer growing season (usually around 5-6 weeks), and their ability to handle drier conditions.
Alternatives like Red King and royal Purple Radish are particularly bolt resistant too, which helps them put energy into developing crisp roots, rather than tall foliage.
We can’t leave without letting you know some of the radish varieties to avoid. For us, French Breakfast are very prone to pithy radish roots because of how fast they crop. White Icicle (like most long radish varieties) are more attractive to brassica pests like slugs and caterpillars.
Often, it’s the more traditional crops that suffer most through climate change, and radishes are one of the biggest signs that temperatures and rainfall in shifting with global warming. The best way to keep growing these fast-growing, early spring crops is to adjust your soil and keep a regular watering routine. If you get that right, you’ll have perfect crisp radishes, not the hollow radishes we’ve seen for the last couple of years.