As I write this month’s column, I am feeling pretty spicy. Not sure if you all know this, but in my daily work, I get a lot of calls, 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 information I would classify as a gardening myth, I get spicy. And to add to that feeling, I was in a monthly meeting with my fellow horticulture experts who 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, 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.
Myth the first. In recent weeks, I have had a few folks share with me they are removing all the wood mulch from their garden beds because it leaches nitrogen away from the plants.
Y’all are just lucky I have a word limit these columns, 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% to 60% humidity, even during the monsoon seasons, and even then, I have seen it pouring rain, and it is registering in the 70% range. If we were in Western Oregon, Louisiana, Florida or any number of other places, 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 our region has an average of 300 sunny days per year. In contrast, some of the South, Northeastern and Pacific Northwest can have up to 220 cloudy days and 180 days of precipitation in a given year.
The reason these tidbits are important about mulching plants and the potential for locking up nitrogen because of said wood chips in this example is largely because of 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 we don’t have much to spare.
Wood mulch 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, mulch will help hold 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, a microbial process will begin 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 organisms to digest and break down 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 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 at Fungal Solutions, right here in Durango.
Myth the second. 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 we don’t get much precipitation in our region (average 18 to 21 inches per year) it can take decades or more to break down needles 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 Horticulture and Agriculture specialist for the La Plata County Extension Office.