Radishes are a quick and easy crop that can really help you to make the most of the space in your polytunnel and can enliven your salads throughout most of the year, especially if you sow seeds little and often to ensure a continual supply during that period. Not only can you grow radishes of all shapes, colours and sizes for their root, you can also let some radishes go to seed and collect hundreds of nutritious and delicious unripe seed pods that are a bit like mange tout but with a slight radish bite.
Radishes are a varied crop and not all are small, round and red. There are all sorts of different radishes with varying degrees of heat and crunch. There are some varieties that are best planted in the spring and others that will be able to remain quite happily in your polytunnel throughout the winter. Choose the right types and be sure to sow small quantities a little at a time rather than planting a whole load at once and ending up with a glut.
Sow radish seeds near the surface of the soil – simply sprinkle a little soil over them and make sure that they receive enough water, and consistent water, throughout the growing season. Radishes grow quickly and so are great to use as a 'catch crop' to make the most of the space in your garden and polytunnel. Since they grow so quickly they can be planted between, or even as row markers for, slower growing crops. Dashing a few radish seeds in with slow to germinate seeds such as parsnips will help to mark the rows so you do not weed out your crops accidentally. Radishes will be ready to harvest long before the second slower growing crop needs the space.
If you would like to grow more sustainably and do not want to buy all your seeds in every year then radish seeds are amongst the easiest to save. As mentioned above, it is also worthwhile making enough space to allow a couple of radishes (you will need no more than two) to go to seed. The large straggling plants will flower, attracting beneficial insects, and then will produce abundant seed pods. Eat some, and allow others to dry completely so you can collect the seeds to sow next year. You may have a few volunteer radishes popping up in your polytunnel the following year but that is all to the good.
Radishes will be ready to harvest in as few as four weeks after sowing. If you continue to sow radishes from March right through to August then you can be eating radishes from May through to January. Simply pull radishes from the ground as needed as soon as small bulbs have formed. In hotter weather the bulbs will be stronger and, as a general rule, the longer you leave radishes in the ground, the spicier they will become.