The second season for cool-season crops will soon be under way as nights get longer and summer turns to autumn. Fast-growing root crops including radishes, beetroot, carrots and turnips are a perfect fit for the autumn growing season, because they start life in warm soil and mature under cool soil conditions. Most can be left in the garden until freezing weather is around the corner. Once harvested, autumn root crops will keep in the fridge for months. Here is a run-down of top root crops for autumn, with seasonal tips for getting them started.
Better Fall Beetroot
Beetroot that matures in cool autumn soil is extra tender and sweet, with greens that are as buttery as spinach. You can speed germination of beetroot seeds by first soaking them overnight, but a 4-hour “washing” process works even better. Place seeds in a glass jar, cover them with room temperature water, and drain off and replace the soaking water every 30 minutes. After 3 to 4 hours and six changes of water, many of the natural germination inhibitors present in the wrinkled seed coats are removed. Drain the primed beet seeds on paper towels for an hour before sowing them.
Most compost-enriched soils contain enough boron for vegetable crops, but beetroot often benefits from a boron boost. As part of soil preparation, mix 1 tablespoon of household borax into a gallon of water, and sprinkle it evenly over the planting bed.
Finally, once your beetroot seedlings are up and growing, don’t forget to thin them. Snipping out excess sprouts with a small pair of scissors won’t disturb the fragile roots of the remaining plants.
Fast-growing salad radishes as well as Asian radishes like daikons and watermelon radishes make great autumn root crops. The warm soil temperatures of late summer enhance seed germination of radishes, which prefer sprouting temperatures of 60 to 80°F (15 to 26°C). Before sowing seed, be sure to cultivate the bed by digging deep, and then use a digging fork to fluff up the soil while mixing in a generous helping of compost. Covering the seeded furrows with potting soil discourages weeds and prevents a surface crust from forming after heavy rains.
Once radish seedlings are up, they absolutely must be thinned to proper spacing: 3 inches (7cm) between plants for salad radishes, and 4 inches (10cm) or more for larger Asian radishes. You can eat young radish seedlings pulled from the garden as microgreens.
Carrots pulled from cool autumn soil are often the best of the year, with fewer imperfections and a crisp, sweet flavour. Fast-growing orange ‘Nantes’ varieties are a good choice for autumn, or you can pump up the colour with orange and red ‘Dragon’ or delicate ‘Rainbow’, which produces carrots in shades of yellow and orange.
Carrots sown in late summer are quick to establish compared to spring crops, because warm soil temperatures shorten germination time to a week or less. I like to plant carrots after spring peas, but any vacant, sunny spot that is easy to water will do. Dig in compost and a scant ration of balanced organic fertiliser, and make sure the bed is well moistened before you plant the seeds.
The biggest challenge to growing autumn carrots is keeping the planted seed bed moist in hot weather. For the first few days after planting, cover the bed with a piece of cloth or a length of old horticultural fleece, folded into a double or triple thickness. You may still need to water every day. Remove the cover after five days or so, when the first seedlings appear. At this point you can suspend a cloth shade cover over the bed to keep the little seedlings from struggling in hot, sunny weather.
And finally we come to turnips, which can be planted later than other autumn root crops because they grow so fast. Mild and crispy Asian turnips taste wonderful raw or roasted, and they mature so quickly that little can go wrong. Revered old varieties like ‘Purple Top’ take longer to size up, but they will keep in the refrigerator for months.
I love the exuberance of turnips and other fall root crops, and how they form vibrant patches of green when the rest of the garden is fading to brown. There’s no better way to close out a productive gardening season.