Gardening with Xpress: On curing sweet potatoes and protecting figs against frost

Greetings gardeners, this will be my last 2022 gardening feature in Xpress. But don’t worry — I’ll be back come spring. I’ve enjoyed answering your questions and sharing what I know to help our mountain gardens be more successful. If you have queries over the winter, you can reach me through Wild Abundance, where I teach gardening year-round.

For this year’s final edition, I’m addressing ways to cure sweet potatoes, options for excess leaves and ideas for keeping your figs warm amid frosty nights.

I grew sweet potatoes this year and I’ve heard that they need to be “cured” in order to keep. Is this true? And if so, how do I do it?

The answer is yes: Sweet potatoes will keep and taste better after the process of curing. When you dig sweet potatoes in the fall, they contain more starches than sugars — meaning, they’re not sweet right away. During this stage, they also have thinner skins, which make them more susceptible to drying out.

Ideal curing conditions are 90 degrees Fahrenheit and 90% humidity for 90 hours (about four days). However, if you can’t achieve those conditions, keeping sweet potatoes in a somewhat warm and somewhat moist space for longer (a couple of weeks) can also do the job. The nonnegotiable components are heat and humidity; if you store sweet potatoes in a cool and dry fridge, for example, they’ll be bland, overly starchy and withered.

I cure sweet potatoes by placing crates of tubers on top of a seedling heat mat with a dish of water on it. Next, I wrap the whole mess in blankets and plastic sheets (old shower curtains work well). This technique can be a little messy, with water dripping down as it condenses inside the curing chamber. If you’ve got a greenhouse or an extra bathroom, laundry room or other indoor space that can be taken over for a few days, these are good options, too. In the case of a small room that can get wet, the whole space can become a curing chamber with the help of a space heater and a humidifier or pot of hot water.

If you can’t achieve ideal conditions, an alternative is to cure them at 65-75 degrees Fahrenheit (the warmer the better) for two weeks, also with humidity as high as possible. Simply wrapping crates, trays or boxes of tubers in damp paper bags or towels can help hold humidity. This won’t achieve 90%, but it will keep them from drying out. You’ll need to remoisten the bags or towels each day.

Once sweet potatoes are cured, they’ll keep best in cooler conditions that are still moist. These tropical tubers don’t want to get as cold as so-called “Irish” potatoes (both kinds of potatoes are originally from Peru). Indeed, it’s best to keep sweet potatoes between 55 and 65 degrees Fahrenheit, with humidity around 60%-80%. Under ideal conditions, sweet potatoes will keep well for several months.

How can I use fall leaves in the garden?

Fall leaves can be a great boon to your garden! In fact, I’ve known many gardeners who drive around collecting bagged leaves from roadsides to bring this generous source of organic matter back to their plots. Whether you gather just your own fallen fortune or scour the neighborhood for autumn’s gifts, there are several ways to use fall leaves in your garden.

First is as a simple mulch: Just dump the leaves on garden beds that are resting for the winter or around the bases of fall and winter crops. It can be helpful to crush the leaves slightly, so they don’t blow away. I like to roll a bag of leaves around a bit to crush them without losing any, then spread them as mulch and water them so that they stick together and stay on the ground.

Another use for fall leaves is to make leaf mold. This is basically a fungal-driven leaf compost that is great as a soil amendment. It can improve water-holding capacity, feed microorganisms and increase organic matter. Leaves are mostly carbon and some minerals, with very little nitrogen. This means that they’re broken down mostly by fungus, rather than a flurry of bacteria and other nitrogen-loving organisms.

To make leaf mold, simply pile up leaves and moisten them. It can help to make a ring of wire fencing to pile them within (this keeps the pile tidy and tall), and to spray water periodically as you pile the leaves. It’s best to choose a cool spot for this project, not in the direct sun. Over time, if the pile stays moist, various kinds of fungus will move in and enjoy the buffet, breaking down the leaves and turning them into a lovely, moist, fluffy friend for your garden soil. If you make a pile like this, you should have leaf mold ready for your spring garden.

Finally, due to their high-carbon nature, fall leaves can be a great addition to a traditional compost pile. Where you might now be using straw to cover up additions of kitchen waste or other green/moist material, fall leaves can also make a great carbon covering. If you simply put fall leaves next to your compost, they’ll be available to layer as you build up the pile.

I have a fig tree that’s loaded with fruit. Is there anything I need to do to protect the tree from frost?

Ah yes, the beauty and tragedy of autumn fruits. Just as many crops ripen to their sweetest, cold weather does them in. This is a normal part of the cycle of the seasons and not to be too worried about. That said, there are some steps you can take to protect your figs from the winter cold.

First, harvest any ripe fruits before a hard freeze comes. Here in the mountains, we have many microclimates, and low temperatures aren’t the same everywhere. If the forecast predicts a hard frost, but your fig trees are close to a building or rock wall, they may be just fine. You can wait and see if the leaves have been frosted before taking further winterizing action. As long as leaves are looking green and perky, the tree is still growing and fruits may still ripen if we get warm enough days following the freeze.

Once the leaves have turned crispy and puckered, it’s time to say goodbye for the year and pull off all unripe fruits. This is also a good time to prune back the tree to a manageable size. Most fig fruits emerge from new growth, so pruning can actually increase next year’s crop. Applying a thick layer of organic mulch (dry leaves, wood chips, straw, etc.) around the base of the tree will help the roots stay warm all winter. Even if the aboveground parts die, most fig varieties will sprout back vigorously from the roots in the springtime. If an extreme cold snap approaches, you can also wrap the aboveground parts of the trees in blankets or cardboard; you could also stuff straw within these makeshift tents to keep the trunk and branches from freezing.

For a few years, we would set up a plastic high tunnel over our figs and string old-fashioned incandescent Christmas lights on the branches. During very cold spells we would turn the Christmas lights on to add a little extra heat. This worked well to keep the figs alive, but then our lives got busy, and we skipped the elaborate treatment last year. Turns out, the figs were fine! They’re hardier than you might think and very capable of bouncing back if they do get nipped by frost.