Here's what Indiana's sub-zero forecast means for your garden

Fret not, green thumbs, the predicted sub-zero temperatures coming this month will not seriously harm most of your outdoor plants.

Indiana is no stranger to extreme cold and neither are most of the plants typically grown here.

The National Weather Service is forecasting a storm system set to hit central Indiana on Friday, bringing temperatures “well below normal” next week. Specific temperatures are still unknown, but NWS said a few morning lows may drop below zero.

Karen Mitchell, Purdue University’s consumer horticultural extension specialist, said protecting plants for winter is a proactive game, and this week is a little too late to do a whole lot.

“They’ll have to evaluate if there was winter injury come April or May,” she said.

Newly planted or young trees could benefit by wrapping the trunk with a tree guard or PVC piping. This isn’t to keep it warm, Mitchell explained, but to regulate the temperature so it doesn’t suffer from a freeze-thaw cycle.

“The bark will freeze at night and the sun hits it in the morning,” Mitchell said. “This is usually very common on the southwestern side of the tree and can cause cracking.”

If these young trees don’t yet have guards, it’s helpful to put one on before these extreme temperatures hit the state. But for more long-term planning, it’s best to put them on in the fall before freezes hit the area and take them off in the spring as temperatures warm back up, Mitchell said.

Scrub Hub:Do you often kill your houseplants? Here's how to keep them alive in winter

The best thing to do before winter is keep the plants watered well and replenish mulch to a depth of 2-3 inches, she said. These tactics help keep the plants stress-free so they are less susceptible to winter injuries.

“The best strategy is proactive prevention rather than being reactive, so hopefully all perennials were well watered going into winter season,” Mitchell said. “So we should be grateful for the rain we are having now.”

Much of the state experienced moderate drought leading up to the winter months, so even though it’s a cold, wet and muddy mess now, the plants are benefiting.

Water-filled soils hold and retain heat much better than dry soils, Mitchell said. This protects the plants from temperature fluctuations that may cause harm.

Mulching also helps soil temperatures, but Mitchell warned against volcano mulching trees. This is where mulch is spread in a mound up to the trunk, which can harm and even kill the tree.

While most plants out in these freezing temperatures should be fine in January, it’s the spring freezes that cause the most harm. New flower and leaf buds are much more susceptible to injury from the cold.

For now, Mitchell advises gardeners to rest easy and stay inside. There's no need to go out and buy all the gimmicks advertised to help plants in the winter, she says.

Karl Schneider is an IndyStar environment reporter. You can reach him at karl.schneider@indystar.com. Follow him on Twitter @karlstartswithk

IndyStar's environmental reporting project is made possible through the generous support of the nonprofit Nina Mason Pulliam Charitable Trust.