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Much of the state and the Sioux Falls region is classified as moderate drought. And when drought is talked about in the winter, it is in some ways worse than if it is in the summer. For two main reasons. The first is, we can’t do anything about it. If the ground was not frozen, we could water to help out the trees (more on this later). The second is, the roots are much more vulnerable to cold temperatures without the insulation that the snow would provide.

Much of the Sioux Falls area is in cold hardiness zone 4b. This means that the coldest temperature roots can get before dying from cold is about 15 degrees F. And while our winter has been mild in some points (like last weeks 60 degrees), there have been a number of times when we have been in some cold temps. According to the SD mesonet climate website, there were portions of eastern South Dakota in January that had soil temps at 4 inches below sod (grass) (where a lot of tree roots are) in the upper teens. The forecast for the rest of February is for below average cold temps. So it is possible for soil temps to dip into that 15 degree range without snow cover. The potential good news is that on Sunday (Feb 2) when I checked soil temps in Sioux Falls at 4 inches bare soil (colder than under sod), soil temps were around 29-30 degrees. That gives us a good buffer for it to cool back down with the cold coming. But what we really need is snow!! Both for soil moisture come spring, but to protect those roots from getting too cold!

If your trees have the recommended 3-5 inches of mulch I never stop talking about, that will help. Wood mulching provides better insulation that sod.

I have received this question a few times this winter, so I thought I would address it in detail. And its a good question. In other parts of the country, winter watering is a thing. But this is in areas where the soil doesn’t freeze like ours normally does.

Tree roots (all plants, really) need the soil temperature to be about 45 degrees or warmer before they absorb water in the normal ways. They can absorb water from freezing to 45 but its greatly reduced and so minimal, that there ins’t a significant benefit to watering plants below 45 degrees (unless its bone dry like it is now). But, the key there is the soil and water cannot be frozen (32 degrees or colder).

So for us in the upper midwest, our best defense against a dry winter (and/or a warm one) is to make sure our trees are well watered in the fall, well before the ground goes below 45 degrees. In drought years, that should start in late August and go through the month of October (generally).

If, we do not get much snow or rain before things green up and the ground is thawed. You should absolutely start watering your trees. But pay close attention to the weather, because if it does start raining, then overwatering can quickly be an issue.

I have noticed that some conifers that did not get watered last year are starting to die from the dry winter. It can be subtle, but any conifer that died in the fall may start having brown needles or just drab dry green needles starting to fall off (think of your Christmas tree after new years…).

I am also concerned that there will be a lot of tip dieback on susceptible trees like maples do the dry fall and cold winter conditions. Sublimation (freezer burn) happens every winter in tree twigs and buds. But if those trees didn’t have enough water in them to keep up for the natural evaporation in the cold, those twigs and buds die resulting in the bare tops come spring green up.

Lastly, we may see some zone 5 plants and some other sensitive trees die from the cold temps and bare soil. I bet many of the bulbs and other perennials in flower gardens won’t fare well with the current conditions. But of course, we will have to see how it all shakes out over the next 2 to 3 months.

Here are a few treecare tips for the last 2 months of winter:

• If you have sensitive plants you area worried about freezing with the lack of snow cover, throw down some straw thick enough to provide some insulation. Just be sure to pick it up come spring.
• If we get an ice storm or heavy wet snow. DO NOT go and knock off any of the ice or snow. Just let it be and melt on its own. You could break branches.
• Take it easy or skip late winter pruning if you suspect your trees are stressed from the drought. You can always do it later.