While 65 degree winter temperatures in Chicago, day in, day out, are cause for jogger jubilation this weather is not doing most of our plants any favors. Our perennials, bulbs, shrubs and trees are being set up for a potential world of hurt. A notable exception is the lovely, naturally early-blooming witchhazel pictured above.
May I set the stage? December was seriously cold. The ground froze early and we had good snow cover to keep it frozen. Great. Now we've had less than 1" of snow in the new year. The soil surface has thawed. We've had minimal rain to provide moisture for roots. Is there anything we can do to lessen the potential damage to our plants? For what it's worth, here's my take on the situation.
Unfortunately, bulbs are making an early above-ground debut. This is most apt to happen in unshaded south or west-facing exposures against buildings. The reflected heat has warmed the soil and led bulbs to believe it's time to rise and shine. Bulbs have built-in insulation mechanisms so leaves and unopened flower buds can tolerate very cold temperatures without damage. Open flowers would be subject to freeze damage. In other words, we're okay for the moment.
What to Do: If you want to be proactive apply an organic (I love leaf) mulch after the soil surface freezes again to keep it frozen to try to slow the bulbs down. Yes, that is an optimistic assumption.
If planted in the past year perennials should be checked for "frost heaving". That is, the edges of the root balls would be 1/2" or more above the surrounding soil surface. Existing partially above grade these roots are subject to temperature and dehydration damage. Such plants are likely to pass on.
What to Do: GENTLY put a foot on either side of the EDGE of the root ball and try to push back into the ground. If dry, water those plants, then (leaf or compost) mulch when the surface refreezes. Remember, mulch roots, don't bury the crown (center) of the plant.
Check plants, especially newly planted evergreens or plants in containers (ex: boxwood or Alberta spruce) for moisture. Dehydrated = damaged, dying or dead.
What to do: If the top inch or so of soil is dry, soak. When the soil freezes again consider applying mulch.
Do you have broadleaf evergreens (rhododendron, azalea, holly, boxwood) in open, sunny windswept areas? Are they dry? If yes, did you water them?
What to Do: While temps are above 40 degrees F. consider applying an antitranspirant spray, Wilt-Pruf for example, to the underside of the leaves to reduce potential dehydration damage for the rest of the winter.
Frost crack is a nasty symptom, occurring primarily on smooth-barked trees. If there's a prolonged period when trees are subjected to temps above freezing during the day, then dramatic drops at night, the expansion and contraction of the bark creates pressure points on the (again) south or southwest sides of the trunks. When the tree starts growing those pressure points may open up creating wounds - sometimes superficial, other times exposing deep fissures into the heartwood. Young (under 6" in trunk diameter): maple, honeylocust, sycamore and linden are most at risk.
What to Do: When the trunk surface is dry you might consider the use of the corrugated paper tree wraps or burlap to shade the trunk. Remove ASAP in the spring (mid-March).
Just because there's no snow cover doesn't mean our yews and arborvitae have a forage-free pass. On the contrary, I was inspecting my garden last week and saw 2 androgynous whitetails belly-high in the neighbors' yews, grazing. Two ear-splitting whistles later they were bounding down the street for a more relaxed dining experience. Very satisfying (for me).
To do: Consider draping the black mesh "deer netting" over yews or around arbs to exclude marauding deer. The netting isn't visible and really is a very effective deterrent. Or spray vulnerable evergreens with the repellent Plant-Skydd. It's also very effective when sprayed on emerging bulbs and daylilies. Deer just hate it!
Now the best we gardeners can hope for is a deep, soaking rain followed by a quick return to sub-freezing temps until the time when spring should really arrive.