End of 2020 Iowa giant sequoia growing season and winter preparation

Another growing season is over. It was a successful one. Despite the drought and a massive wind storm that literally changed the landscape for hundreds of miles, this little experiment lives on.

As reported earlier in September, there was practically no fungus attacks this season. It was probably due to a generally drier than normal summer but also probably because of the consistent application of an anti-fungal agent, chlorothalonil. Healthy green and blue-green looking trees are going for their winter hibernation phase. After trying several winter protection strategies in the previous years, this year I decided to try a different approach with some extreme winterization experiments. 

During the upcoming winter I decided to tackle two major variables  - water evaporation through the needles and root access to liquid water. For the former, I sprayed the foliage with anti-desiccant polymer and then wrapped the trees in some frost cover fabric, which is very light unwoven material. I used 3/8 inch rebar that is used in cement work to create pyramidal frames around single and groups of sequoia seedlings. It's an extremely cheap and simple way to construct a structure around trees. 10ft long rebar costs about $3.50 a piece. Sticking rebar in the ground and tying three or more ends with a zip-tie takes only a minute creating an improvised teepee. After the trees are wrapped in fabric and teepee frame is constructed, then I used a roll of wide packing plastic to create a winter/moisture barrier by wrapping it around the metal frame. 

I made sure to leave a hole on the top of the teepees that would allow extra moisture to escape the housing. There are some variables in the set up as I used more or less wrapping material and bigger and smaller holes on the top to control amount of evaporation. 

After the teepees were constructed I watered all sequoias with generous amount of water and buried the area around the pyramids with 6-8 inches of mulch.

Which brings us to the next topic of root water access. 

It is clear that sequoias are greatly affected by the loss of moisture during cold Iowa winters. In general, it is stated that this area in Iowa has 3 to 4 feet deep frost line for the purposes of house and other structure construction. In my own experiments I find that it's actually closer to 2 feet, but I can certainly see how it can get deeper during extremely cold winters. Once the ground is frozen solid there is little that sequoia roots can do to replenish lost needle water. Some trees adapted to these conditions and remarkably many local conifers can survive a total root freeze, but realistically, not every seedling of even the hardiest of them all - eastern red cedar - survives such conditions. I had dozens of red cedar seedlings perished during winter. Needless to say, sequoias are not as hardy as red cedar. Controlling the way how the roots fare during  winter would be an interesting endeavor. 

The idea is that as the trees get older and develop their root system, enough of the roots would penetrate the frost line, providing the tree with water during cold winter months. The feeder roots of sequoia are located very close to the surface, which creates a clear problem for growing sequoias in such a harsh climate. The challenge is to create ground conditions that would allow for some liquid water to be available to the trees. One most direct way is to cover ground with a thick layer of mulch. However, in some previous years I did have some trees with 6-8 inches of mulch and they still did not survive. The difference this year is that I am applying both thick mulch layer and adding a moisture barrier for the needles. My hope is that the combination of both would allow survival. 

But wait, there is more.

How do I actually know if there is liquid water available to the roots? Fortunately, there are wireless sensors available these days. I did not find any examples of people using some underground sensors for gardening or tree-growing over winter. I did find out that there are sensors that are used in food freezers, which indicates that they will probably work if placed in the cold soil. I purchased one such sensor called "SensorPush"

I have been testing it for a couple of weeks and so far it seems to perform well. The basic concept of the experiment is very simple - place a sensor at the level of the feeder roots and see if temperature is anywhere close to the water melting point. I dug a hole about 6 inches deep next to one of the sequoias and placed there a SensorPush, which I put in three enclosed plastic bags to prevent exposing it to open water. Filled the hole with soil on top of the sensor.

I added another 8 inches of mulch on top of the filled hole and marked location of the sensor with an old arrow.

Next step was a familiar teepee with wrapping of the needles in fabric and plastic around the frame. And another 6 inch of mulch on top and around the base of the pyramid:

Here are the results of the first two weeks of sensor measurements:

It is worth mentioning that the lowest temperature so far was the night from Nov 22 to Nov 23, 20F. There was a delay of almost 24 hours for the ground temperature to reach its lowest value of 45.3F during the night of Nov 24. The 25 degree difference is substantial. It is clear that the ground gives off immense amount of heat at this time. How this will continue during the winter months will be interesting to observe.

But that's not all. To push the experiment even further I added a controlled variable in the way of an underground heating wire. The SensorPush sensor is actually lying on top of a section of this wire. The wire is a 6 foot long loop that goes around this sequoia seedling at the depth of 6 inches. If and when the temperature drops below freezing I intend to conduct some power injections to see the effect on the soil temperature. Depending on the outcome of these experiments, it would not be too difficult to install underground wires for other trees, but the time will tell if this is needed or if it's effective.