Watering when temperatures are below 32 F

I moved to Colorado Springs, CO last April, 2020. Which means I have not experienced even one full year of seasons here along the front range of the rockies. And I’m a rank beginner at Bonsai development. A few weeks ago it was 90 degrees fahrenheit in the day and then the temperature dropped radically and it snowed the next day. In one of Ryan’s streams he mentioned those of us living along the front range of the rockies experience radical changes in weather conditions. I can in deed attest to that.

I’ve been watching Mirai live streams on fall wrap ups and preparing for winter. I’ve learned a great deal about how the trees need to experience changes in temperature down to 28 F to prepare for the spring push. Lots of great information in the streams. However, did I miss something about watering when the temp drops below 32 F?

The temperature here at night for the past week has been bobbing down and up from 30’s to 50’s. The forecast says we will be dropping into the 20’s over the next few days with snow falling on Sunday evening.

OK! Here is the question: During the summer hot days I was watering the trees twice a day, very low humidity here in the summer . This morning after a night 25 F I came out to assess how they were doing (waiting for my chinese elm to drop its leaves) and found the pot soils frozen. Does one water when the pot soils are frozen? The bigger questions is what are the watering routines during periods below 32 F???


Once the pots freeze there is no need to water the pots since the water will not soak in and the amount of water the roots can take up is very, very limited. On the other hand, the upper part of the tree can still transpire - particularly if it is above freezing and exposed to the wind in a dry climate (i.e. the Front Range). As a result, it is important to protect the trees from desiccation under those conditions. A blanket of snow that covers the trees without crushing all of our work is just about ideal, but it never seems to work that way. If your trees and pots fully freeze and they are protected then they will not need water until they thaw, but a little water to make sure the surface of the soil does not freezer burn is a good idea. Unfortunately, on the Colorado Front Range your temperatures will cycle from well below freezing to well above freezing and back several times - often within a week.


Put then on the ground under a bench away from sun and wind and cover with plastic sheeting. Toss snow in when available. That will keep the pots consistently just below freezing and the air humidity up. Works for me in Flagstaff, similar climate to yours.


While not in CO, I can attest the wind is the main winter enemy. I keep pots mulched in on ground protected from direct, usually northern winds.

Winter watering can be tough, and you already have some of the reasons why. Wind, sun, more wind, freezing, all make it tough to water correctly. Plus there are some factors to watch out for. Roots should never dry completely, or they can be damaged severely, or killed. On the other hand, watering just before a deep freeze can also kill roots. The best way is to watch for those days when your pots are thawed, and a super cold night is not forecasted. Any time you water, there must be enough time for very good drainage BEFORE sub-freezing temps get there. If water freezes around the roots, you can end up with a damaged/dead tree


The dramatic shifts in temperature are hard to predict especially when I’m focused elsewhere. I certainly have to pay more attention to the forecast. AND! Yes, I do believe I’ve killed a couple of trees in the deep freezes we’ve had lately. Most live in the house now until I can construct a shelter. Just installed a weather station to help me understand the seasons. Not only are there freezing temps here along the front range of the rockies, there are also desiccating winds. We recently had a windstorm with average wind speeds in the 30 mph with gusts up to 50 mph. I’m now looking for a way to record the data in a file so I can create graphs. One thing I’ve done is used 2" foam insulation (from Lowes) around a ponderosa pine in a wooden box. Seems to be working so far. This is the way in Bonsai . . . :face_with_hand_over_mouth: