As I write this month’s column, I am feeling pretty spicy. Not sure if you all know this or not, but in my daily work, I get a lot of calls and emails and walk-in questions about everything under the sun related to gardening, trees, plant diseases, lawn care and more — pretty much any topic you can think of that involves things that photosynthesize or the soil beneath.
So, when I hear that some of my favorite local gardeners are sharing gardening info that I would classify as a gardening myth, I get spicy. And to add to that feeling of spice, I was in a monthly meeting with my fellow horticulture experts that are also hearing things that sound an awful lot like information that was garnered through AI. Oh, so spicy.
That led me to my topic for this month: garden myths. I am super happy to play devil’s advocate here, and if any of you disagree with me or have an alternative perspective, please don’t hesitate to send me an email (but I expect you to cite your work). That said, I am only using sources from credible, peer-reviewed papers. I have more than a few thoughts about AI, but that’s for another day, or perhaps over margaritas.
The first myth: In recent weeks, I have had a few folks share with me that they are removing all their wood mulch from their garden beds because it leaches nitrogen away from the plants.
Y’all are just lucky that I have a limit on how long these columns are allowed to be, because I have so much to say about this. First things first. Using wood mulch (or any organic matter) to cover the soil around trees, flowers, shrubs, etc. is one of the best ways to limit the desiccating effects of solar exposure.
We live in a part of the world that rarely ranges from 10-60 percent humidity, even during the monsoon seasons, and even then, I have seen it pouring rain and it is registering in the 70 percent range. If we were in Western Oregon, Louisiana or Florida, or any number of other places around the country, you can be certain of a hot, wet, very humid lifestyle. Having lived in four southern states in my younger days, I can attest to feeling like I was in a swamp most of the time.
In addition to our low humidity, we are all basking in the fact that our region has an average of 300 sunny days per year. In contrast, some of the south and northeastern states or Pacific Northwest can have up to 220 cloudy days and 180 days of precipitation in a given year.
The reason these tidbits are important to understand when I talk about mulching plants and the potential for locking up nitrogen because of said wood chips in this example is largely due to our overall climate. For wood chips or any plant matter to breakdown in a significant way, you have to have the right conditions. That includes water and, outside of our irrigation, you know that we don’t have much to spare.
Wood mulch that is not from fresh green tree residue is basically just carbon. When added to the surface of soil around plants and trees (never too close to the base, please), and we irrigate our plants, the mulch will help hold that moisture in the soil longer, provide a cooler soil temperature, and prevent loss of soil on a windy day.
No, wood mulch is not perfect, and, yes, if wood chips are buried in the soil there will begin a microbial process in which nutrients, including nitrogen, are breeding grounds for life and for a short time, months to a couple years if minimal water is present, the nitrogen will become used by the organisms to digest and breakdown the wood material. Now, that does not mean the same thing for the mulch bits that are on the soil surface. The contact zone where soil and mulch meet are going to produce 5 mm or less in nutrient disruption.
One of the most fascinating research efforts that I have seen recently comes in the form of inoculation of wood chip mulch with specific mycorrhizae (fungi) strains that increase the water-holding capacity of the mulch and stimulate surrounding soils. Again, this is scientifically researched and tested repeatedly through a local expert right here in Durango.
The second myth: This one usually brings a smile to my face, but I do hear it several times each year. If I have a lot of pine trees, will the soil be more acidic? Or, can I acidify my soil too much if I use pine needles for mulch around my plants?
The answer is a resounding no. Pine needles are not very acidic by themselves, and when you remember that we don’t get much precipitation in our region (average 18-21 inches/year) it can take decades or more to break those needles down into soil organic matter. Besides, the reason the East Coast has acidic soil has nothing to do with evergreen forests. Rather, that is a process of the water cycle (of which they have a lot of water), chemical leaching of hydrogen and aluminum, incredibly old granitic bedrock, with a lot of plant decomposition and other organic matter. That’s all I have on that for now.
Heather Houk is the La Plata County Extension horticultural and agricultural specialist.
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75th annual Archuleta County Fair
The 75th annual Archuleta County Fair kicks off today. Visit archuletacountyfair.com to learn more.
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