Cold Snap Coming; More on Leaf Mulch

Our unusually warm and sunny November is over with the first of the winter’s cold snaps predicted to start dropping temperatures tomorrow. Time to finish mulching the garden! Lows of -4 to -6oC [20-25oF] may materialize by the end of the week and that is getting pretty nippy for winter lettuce and salad greens. Be ready to throw a tarp or plastic sheet over those beds if you are in colder inland or higher elevations locations. The shoulders of carrots, beets and other roots showing above ground can be damaged if they are exposed but will be fine if they are mulched. Winter varieties of cabbage, kale, broccoli, Brussels sprouts, leeks, etc. are hardier to lower temperatures and will be fine.

If you have outdoor citrus trees this is the last chance to install heating cables or Christmas lights and cover the trees with plastic or row cover fabric. I switched from using incandescent Christmas lights to using plumbing heating cables on my lemon and lime trees with good results (any hardware store has them; they were on sale at Home Hardware last week…). The cables only draw 80 watts and have a built in thermostat that automatically turns on the cable when it gets close to freezing so you don’t need a separate control as you do for the lights. But whatever you are using, time to have it in working order!

I thought I had said all I had to say about leaf mulch in the last message…but, nope! There were still questions about whether using leaves would spread pests or diseases. Even if pests or diseases were present they wouldn’t be able to attack an unrelated plant because most insects and nearly all disease organisms are very host specific. So the black spots that you see on maple leaves, which are caused by tar spot fungus, couldn’t spread to any vegetables, flowers, fruit. Most importantly, even if the dead leaves show insect damage, the insects are long gone at this time of year, having crawled off to find a place to send the winter. Pathogens are dormant now as well as spores or other durable stages, some under bud scales, others in the soil, on mummified fruit, etc. and not on the leaves. There are some exceptions: apple scab (and pear scab) spores overwinter on the fallen leaves, which is why apple leaves should be composted or mowed over so they decompose before spring. But if the leaves were raked up and put on unrelated plants they wouldn’t cause disease in those plants.

Another concern is that people worry that they will have more slugs with leaf mulch. Slugs are decomposers and when they are breaking down dead leaves they are doing their job. If they are busy doing that, they are not eating plants. In any case slugs don't disappear and leave the plants alone: if there are no leaves on the soil, they will just eat the more of the plants. Mulches also harbour important predators of slugs, such as ground beetles and rove beetles.

November 26, 2019 12:36 PM

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