bunch of radishes

How to Grow Radish

Radish is a cool-season crop that can be grown in spring, autumn and winter in your Harvst. They mature quickly and can be white, red, purple or black and have round or long tapered roots.


Because Radish is a cool-season crop it is best sown in the spring and late summer. Sow every 2 weeks for a continuous supply and they take anywhere between 18-70 days to mature depending on the variety. However, when the days are long and warm in summer, radishes will immediately bolt rather than forming a delicious snack so avoid growing them then. 

When growing radishes in your Harvst S-Series Mini Greenhouse it is important not to keep the tray too warm or have the lights on for too many hours as it can make them bolt. The ideal growing temperature is 15-19°C but radish seeds germinate from as cold as 7°C to 25°C. Outside this range they will struggle and it is also worth noting that they take longer and are more erratic to germinate when the temperatures are cold. However, the seeds tend to germinate in around 7-14 days. 

Radish is easy to grow from seed and can be direct sown or transplanted later. It is therefore a perfect crop to sow in your Harvst as it can stay in there till it matures or be transplanted outside. 

Fill a tray with a general peat free multi purpose compost and water it. Sow the seeds a couple of cm apart and sprinkle 1cm of compost on top. Press down slightly to make sure that the seeds are in good contact with the compost and carefully water again. 

If you’re using a modular tray then put 2 seeds per module and plant out as they have germinated.  

Keep the soil evenly moist until seeds germinate because if they dry out they will most probably not germinate at all. This can be aided with a plastic dome over the tray but it is not a must.  However, as a general rule, the colder the soil the less moisture you need.

Plant care 

Keep the soil evenly moist throughout the growing season as irregular watering can make the radish woody and super spicy!

Growing options 

You can choose from one of the growing options below or do a combination of 2 or 3!  However, whatever growing option you choose, keep radishes evenly watered so that they grow quickly. Slow growth causes them to go insanely hot and woody. Also, keep an eye on your grow lights and give radishes a maximum of 8 hours of light. 

  1. Grow till maturity in your Harvst: When the seedlings have emerged, thin them to 2.5cm apart for smaller varieties and up to 10cm apart for larger winter radish varieties. This can be done by cutting the rejects with scissors (you can eat immature leaves as a salad!) or carefully using a stick/pencil to loosen the soil and lift the seedling up by its leaves and transplant to elsewhere. Make sure they are big enough to handle before you set out to do this. They transplant remarkably well but try to disturb the root as little as possible. 
  2. Plant outside: When the seedlings have developed their true set of leaves (not the first set appearing but the second set) they can be transplanted out into your garden. Space them 2.5-10cm apart depending on the variety. If you have problems with slugs, keep them in your Harvst a little longer. A bigger plant can resist a slug attack much better! When planting outside it is best to make sure that your soil is great before planting by adding well rotten manure or other organic material so that it’s full of nutrients for your plants. When transplanting seedlings, ideally plant out early morning or evening and/or on an overcast day. Avoid planting at peak sun times or on windy days as this can cause sun or windburn which can lead to death! If you have used a modular tray then pop each module in the ground 5cm apart. 
  3. Container Grown: Radishes grow well outside in a container but try to choose one that is at least 15 cm wide and tall. Space them 2.5-10cm apart depending on the variety. As radish is heat-sensitive, move containers into the shade on warm days and keep in mind that containers will warm quicker than garden soil in spring and that radish must have constant moisture in the soil.


Spring radish varieties usually require 18 – 30 days to be ready whilst winter radishes require 50 to 60 days. How big they should be depends on the variety and it’s best to either lift a couple to check or push the soil aside to decide if they are large enough to harvest. In any case do not leave them in the ground too long or they will become woody.

Watch out! 

Radishes can be attacked by aphids, flea beetles and root maggots. Aphids are best treated by showering the plants and flea beetles can be kept at bay by netting and keeping the soil moist at all times. Flea beetles usually just make the leaves unsightly rather than affecting the growth of the root. Root maggots are more likely to be a problem when growth is slow and in the summer. Therefore, try to stick to growing them in spring, autumn and winter and keep an even moisture level in the soil to speed up the growth. 

Pro Tip

Sow often, harvest often should be your mantra when it comes to radishes!

Nerdy facts

The Botanical name for Spring radish is Raphanus sativus and winter radish is Raphanus sativus longipinnatus. They originate from the temperate regions of Asia.

Recommended Varieties

Here are some great varieties but there are many more fantastic varieties to choose from!

Spring varieties can be grown in spring, autumn and winter in your Harvst and some great varieties are ‘De 18 Jours’ which mature in just 18 days under ideal conditions. It has cylindrical roots that are red with white tips.  ‘French Breakfast’ is also a crisp and crunchy variety with cylindrical roots with a strong, peppery flavour. 

Winter radishes are larger, oblong, and can grow up to 20cm long.  ‘Black Spanish’ is about 10 centimeters in diameter with a  thick, rough, and coarse black skin. Underneath the flesh is bright white, firm and crisp with an earthy and spicy taste when raw but can also be cooked. It is usually ready for harvest in 55 days.