After months of technical and other problems (started when my computer literally melted down while I was using it- melted- it *ucking melted). I am back with a new blog post and it will now be on a regular schedule. This blog as you might remember focused on weather and gardening. A subject I am very passionate about. Weather is a little confusing to the average lay person. We all experience it and we have been educated by the media about weather forecasts. I will continue to focus on shedding a little light into the relationship between it and gardening. Again, this is about Portland, Oregon of which i am most familiar and where I garden.
Sacramento or Portland?
A lot of weather has happened in the last few months and as you have all experienced its been unprecedentedly hot and dry. Our mild dry spring morphed right into a blasting hot June (hottest on record at PDX) and has continued right into July. As I write this we are about to experience a reprieve from blasting hot- to actually below normal. It may even sprinkle. Then its back to toasty conditions by the middle of next week. Some numbers that I have found interesting are that we not only broke the record for most days above 90ºF in June, we are on track with the coming heat wave to break our annual record for most days above 90ºF total. That record was 23 days back in 2009 and as of today we’ve had 18 days above that mark. The forecast beginning Thursday for a blasty 95ºF also includes at least three to five subsequent days in the 90’s and the news for August kind of sucks if you don’t like heat. So, we’ll more than likely tie that record and we still have the hottest part of summer to go. By the way we average 14 days above 90 in an average year. And one day of 100ºF.
You thought your water bills were high in July
As far as forecasts go we are expected to stay with torrid conditions. Long range forecasts for August paint a picture of very hot conditions- the first week of August is traditionally our warmest of the year. Both all time records, records and averages bear this out. Our all time high of 107ºF which has been reached at PDX three times occurred last in the first week of August 1981. That heatwave was by all measures the most intense ever. The temperature remained above 100ºF for 5 days. 103ºF, 107ºF, 105º, 107ºF, 101ºF respectively. I mention this because it does put this year’s heat in perspective. It could be uncomfortably worse. So far our warmest at PDX has been 97ºF on three separate occasions. (More about that later) But averages are where its at and this year has some remarkable bench marks. As you probably have noticed not just the highs but the lows have been steamy. We are on track to beat last years record for most lows above 60ºF. And as I’ve said before climate change will come in subtle ways and not always be blastingly overt. There has been much discussion about why this is happening. Everything points to much warmer sea surface temperatures in the north Pacific.
Its all about the flow
Onshore flow from the Pacific not only modifies our temperatures it mixes the atmosphere on a daily basis. During the day the flow is to a limited extent off shore and at night the flow usually switches to onshore. This brings a cooling blanket of marine air that we recognize as our wonderfully comfortable sleeping weather. Temperatures frequently dipping into the 50’s to near 60ºF. This year there is a blob of warm water in the upper parts of the ocean and without boring with details it is causing our onshore flow to be modified and warmer. An example of this was the the 71ºF overnight low in late June that shattered all existing overnight low warm records for the month. Though the high was only 95ºF that day we just couldn’t get the sweet enervating cool down provided by the typically cool North Pacific. And this trend has been persistent. So far in July only 2 (just two) of 24 days have had lows below average. In fact, 18 days have been above 60ºF. Our warmest average overnight low occurs at the end of this month and that is briefly 60ºF on the nose. So, this pattern has been stubborn and its had an affect on our gardens. Continuing with the theme of 2015, everything is at least a month and some times more ahead of schedule.
The Crape Myrtle in the Coal Mine
One reason I like Lagerstroemias (Crape Myrtles) is not just because I find them pretty but they act as natural heat absorbers and like a really gaudy thermometer they tell you just how much heat has accumulated. They require (and not all cultivars are the same) a certain number of hours of heat above 85ºF which gives them the signal to cease growing and start blooming. To complicate it a bit they are sensitive to warm overnight lows as well. And just as you would have expected they have all burst into bloom around town. I have never seen this display so uniform and so early. They have been quietly recording our hot year and despite the dusty dry conditions this signal has over ridden lack of moisture and they are going for it. So the combination of sustained high temperatures and warm overnight lows is recorded thusly. Not only are Crape Myrtles early but other heat sensitive plants have followed suit. This is the earliest that Vitex (Chaste Trees) Caesalpinias, Pomegranates have all come into bloom as well. One nice thing about a hot year- it allows the wood of these plants and most others to ripen well and can actually lead to increased cold hardiness the following winter.
Um…Who put the thermometer there?
One gripe I have is that the recording station at PDX is placed in a very odd location. Its located just feet away from the cool Columbia River and this has an impact on the readings. So far, we’ve hit 97ºF as our warmest daily high three times. But away from PDX temperatures have been routinely 5 sometimes 8 degrees warmer. In fact, as an example, in my own backyard I’ve hit 100ºF and 101ºF already. You can look up the most local recording stations on the NOAA observations page (click Portland/Vancouver metro observations) I’m substantially farther away from the huge cool river and it shows. So, if you have noticed in your car thermometers or bank signs or your own backyard higher readings. You aren’t crazy. What is crazy is where PDX takes its temperatures. The cool breeze off the river, I am sure is the culprit.
97º- What is it about 97ºF?
I have noticed since I have been obsessing over plants and weather that there is something about the benchmark of 97ºF where plants go from thirsty and wilting to burning. Last week when I hit 101º in my backyard (away from the Columbia River) I noticed that plants really began to suffer at 97ºF. For instance when it gets that hot my Telopea almost always records scorched leaves. No matter how much I water it. Certain perennials flag at that temperature too and I’m sure that is why so many Hydrangeas around town look like shit. On that day the relative humidity dipped to less than 10% as well. Scorching for plants that are not naturally drought adapted. I’ve noticed Rhododendrons around town that have scorched as well. There is something about 97ºF that a lot of our plants can’t handle. Remember that plants are Mesic (water loving ) to Xeric – ( they have adaptations to avoid moisture loss.) My best advice, is to water heavily, BEFORE and not during the heat wave to get the water up into the tissue to prevent scorch and cell damage. By the way, remember that it is better to water deeply and infrequently, than just sprinkling water on the surface of the soil every day. As my friend Magi recently posted. Water and then even if you have to drill down into the soil with a screwdriver to check, make sure the water is going down. It can also help to scratch the surface of the soil to prevent a crust from forming that can actually repel water. And of course. MULCH, MULCH, MULCH.
There is no reason not to plant right now.
Finally, one effect that I’ve seen is that people just do not want to plant during hot conditions. This makes sense. I wouldn’t. But in between heat waves is a great time to plant. Why? Because soil temperatures are high and plants will take right off if looked after. One way to deal with planting in dry conditions is a method I’ve developed over time. Dig a hole twice as big as the root ball. Fill it with water. Let the water drain completely (be patient), then fill the hole with water again, and let it drain completely (still being patient) then fill the hole a third time and place the rootball of the plant in the water in the hole and backfill, not only will you soak the roots this will eliminate any air pockets that may occur. Then mulch. This methods wets the soil column directly below the plants and gives roots a reason to go down. Water the plant normally after that when it becomes dry. Try it, I guarantee, it works when you are planting into dry soil. And of course MULCH, MULCH, MULCH.
One last remark. YES, it has been extremely dry. We have had much below average precipitation for the past three months. Our consistent high temperatures have literally sucked the moisture out of the soil. All the more reason to water deeply. And MULCH, MULCH, MULCH.
Thanks, Happy Gardening,