The 2021 growing season is about to kick in high gear. There are already hints of the new growth on the surviving sequoias. In this report I will talk about overall survival of the sequoias made up of several verities of the species, followed by the discussion on the underground temperature measurement and the heating experiment that was conducted this winter. Finally, an irrigation system is being installed around the sequoias to further super-charge the project, so will talk about that at the end.
Bottom line up-front - things went well this winter for the sequoia park.
Winter Summary
Overall, this was an average winter with warm December, moderately warm January and a very cold spell during the month of February. All temperatures in Fahrenheit, data taken from the Iowa Department of Agriculture.
The month of December started off fairly warm with a few days in the 40s and ended up with 7 days in the 40-degree range and 3 days in the 50s. Overall, the average high temperature for the month of December was 35.1 degrees, which was around 3.3 degrees above the normal high for December. Our average low for the month was also above normal. Two big snowfall events in Cedar Rapids ended our snowfall total at 13.5″ with a few trace amount reports. That’s 5.7″ above the normal amount of snowfall we see in the month of December.
In January, stations in Eastern Iowa reported average temperatures one to three degrees warmer than normal. January’s statewide average maximum temperature was 31.1 degrees, 2.5 degrees above normal while the average minimum temperature was 16.5 degrees, 6.2 degrees above normal. A majority of the state’s National Weather Service co-op stations reported near normal to slightly above average precipitation during January. Several winter systems moved through Iowa leaving behind measurable snow statewide. Over the month, a band of 15 to 20 inch total accumulation.
February’s statewide average maximum temperature was 20.7 degrees, 12.7 degrees below normal while the average minimum temperature was 4.4 degrees, 14.5 degrees below normal. The coldest period of the month was between February 7th and 16th when the average temperature was -5.2 degrees, 27.2 degrees below normal. Temperatures did not rebound to normal until the final eight days of February. A majority of the state’s National Weather Service co-op stations reported near to slightly below average precipitation in February.
Survival stats
All but two sequoias planted in the ground survived, some better, some worse. All sequoias kept in the containers in the shed perished. All containers had some heating at the bottom in the form of the ice melting electric blocks. The bottoms of the containers were in some liquid water with just above freezing temperature. Surprisingly, this was not enough to keep them alive and 100% died.
All in-ground planted sequoias had approximately the same level of protection. Taller ones had some unwoven fabric wrapped around individual trees and covered on top by the packing plastic film wrapped around rebar pyramidal frames. Shorter ones had foam cones providing superb insulation. Rebar-based "tepees" can be scaled for many winters to come, providing winter wind protection while the rest of the park made of the native spruce, pine, red cedar and fir species had time to grow up and provide a micro-climate for the site.
Here is more in-depth data on specific types of sequoias and how they fared:
- HS is Hazel Smith
- EB is Exceptionally Blue
- OR are the regular variety (not cold-hardy) the ones from the Oregon Scenic Hill nursery purchase a few years back and
- Regular are my own grown from J.L. Hudson seeds
- 0 - dead (no stats on container grown, since 100% perished)
- 1 - survived with significant damage
- 2 - survived with minimal damage, brown tips and occasional brown branches
- 2.1 - survived with no visible damage, entirely green
Here are some examples of 1s and 2s, starting with the ones that did best:
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| Hazel Smith with no damage after winter |
And here is a zoomed in view of the same sequoia that shows new growth:
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| Hazel Smith showing new growth by May 1, 2021 |
Now for the majority of sequoias that had some damage and remain mostly dormant for now:
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| Hazel Smith with some brown tips, dormant for now |
And here is a zoomed view that shows minor damage:
As it was expected the temperature kept falling at 1ft depth towards freezing throughout December and January. With an extra 6-8" of mulch on top of the soil the gradual slide was surprisingly slow. However, the deep freeze in the beginning of February accelerated the temp fall and by Feb 15 it became clear that the ground was going to freeze within a few days. On Feb 15, the heating wire was turned on for the first time, which is clearly visible on the chart as a steep jump in temperature from 0.7C to 6C. The heat was turned off on Feb 21 and the temperature promptly fell to 1.5C. Another heating event started on Feb 27, leading to another jump to just above 6C. There were several power interruptions in the next few days and the power was finally turned off on Mar 7 as the temperatures started to climb above freezing outside. The fluctuations on the right side of the graph are natural temperature changes as the snow melted.
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| Hazel Smith with brown tips and no new growth yet |
Finally, a couple of examples of 1s:
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| Hazel Smith with major lead gone (cut off) but some green side branches show new growth |
And another example with significant damage but still alive
Ground temperature findings
Here is a graph of the underground temperature:
As it was expected the temperature kept falling at 1ft depth towards freezing throughout December and January. With an extra 6-8" of mulch on top of the soil the gradual slide was surprisingly slow. However, the deep freeze in the beginning of February accelerated the temp fall and by Feb 15 it became clear that the ground was going to freeze within a few days. On Feb 15, the heating wire was turned on for the first time, which is clearly visible on the chart as a steep jump in temperature from 0.7C to 6C. The heat was turned off on Feb 21 and the temperature promptly fell to 1.5C. Another heating event started on Feb 27, leading to another jump to just above 6C. There were several power interruptions in the next few days and the power was finally turned off on Mar 7 as the temperatures started to climb above freezing outside. The fluctuations on the right side of the graph are natural temperature changes as the snow melted.
One conclusion from this data is that the wire definitely works but it's unclear how much of the soil is heated around the wire. In this experiment the sensor was placed very close to the wire, about 3 inches (5 cm) above it. For the future experiments another sensor will be placed another foot below wire depth to measure the temperature gradient.
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| Exceptionally Blue with soil heating wire. Arrow indicates placement of the temp sensor |
The Exceptionally Blue sequoia that had the wire installed fared well as compared to other sequoias and there are no significant differences with most of other sequoias.
Irrigation system
To be added. Literally, the irrigation system is to be added! Why?
