I would like to know if I can leave unharvested carrots to rot in the ground. Is it bad for the soil, since there’ll be a new planting the following spring?
Actually, things will be turning out quite differently from what you are imagining. To start with, unless there’s a flood and the carrots sit in soaking water for weeks, they’re very unlikely to die over the winter. So, let’s take a step back and see what really does happen to unharvested carrots left in the ground over the winter.
First, the carrot (Daucus carota sativus) is not an annual. Unless something goes seriously wrong, it won’t die over the winter. Nor will it rot.
Instead, the carrot is a biennial: it lives for 2 years. The first year, it produces a rosette of deeply cut leaves and also the long, thick, tasty taproot that we know so well. Its root serves as an energy reserve for the carrot’s 2nd year. The root will die, though … after year 2!
If you leave a carrot root in the ground over winter, it won’t die or rot, but will remain dormant (at least, if you’re in hardiness zones 3 through 9 or a protected spot in zone 2). In early spring, the plant will regrow from its root, again producing a new rosette of leaves, but this time also a tall, upright stem. This stem will bear umbels of white flowers. Once the flowers are pollinated, seeds will form and mature. It is only when they fall to the ground at the end of the 2nd summer that the plant, having accomplished its life work, dies.
Most home gardeners only see the first part of this cycle: from sowing to harvest. And pulling the plant to harvest its root conveniently kills it. So, it seems perfectly normal to us that a carrot would die at the end of the first season. Also, the majority of the other vegetables we know are annuals: peas, lettuces, beans, sweet corn, etc. They too grow from sowing to harvest to death from spring to late summer or fall. But if you let a carrot grow on its own, its behavior is very different.
If you had asked your question about an annual vegetable, let’s say lettuce or cucumbers, my answer would have been very different. You would want to remove any viable seed to keep them from self-sowing too abundantly, of course, but otherwise, you can just let their leaves and stems rot on the spot.
You see, rot is not a bad thing. It doesn’t harm the following summer’s crop and its causes no problems to the soil. What it does do is enrich the soil. This will leave you with richer, humusy earth that needs less compost or fertilizer. In other words, letting dead vegetables rot where they grow is of great benefit for your vegetable garden! Indeed, one of the basic principles of laidback gardening is to let crop residues return to the earth. Well, there you go!
This is especially true of the vegetables known as legumes (peas, beans, soya beans, broad beans, etc.). You’ll definitely want leguminous vegetables to “rot on the spot!” They accumulate nitrogen—the most volatile mineral and one most sought after by plants—in nodes on their roots. It’s by leaving these nodule-spotted roots to decompose in place that they’re able to enrich the soil in nitrogen.
Hardy biennial vegetables, such as carrots and parsnips, will still be alive in your garden next spring. However, unless you harvest them very quickly, soon after the snow melts, you won’t be able to eat them the second year. That’s because as soon as they start to grow, they quickly drain sugary reserves from the root and use them to nourish their flower stalk as it grows. After all, that is what they evolved to do. Therefore, last summer’s plump and juicy root will quickly become skinny, fibrous and dry with an unpleasant taste.
Unless your goal it is to harvest fresh carrots all winter (possible in fairly mild climates or under a really thick mulch), there is really no logical reason for leaving rows of carrots standing in the garden all winter*. All those flowering carrots will occupy valuable vegetable garden space the next summer without giving anything (except seeds) in return. And by the end of the second summer, they will have impoverished the soil rather than enriched it!
*True enough, if you wanted to produce your own seeds, you could let one carrot overwinter. That would give you enough seed for several packets.
What to Do?
I suggest harvesting your carrots this fall and finding a way to store the extras for the winter. There are a few ideas on the subject in this article: How to Store Carrots. That way, you’ll have homegrown carrots for the whole winter season and even right through into spring … and a vegetable garden free of aging carrots and ready for whatever fresh crop you intend to grow next spring!