The wrong time to trim trees

Summer’s the wrong time to be trimming trees

Rich in Fairfax Station writes, “I help a neighbor lady who has a large River Birch that’s very close to her front door. She wants to remove some branches that are beginning to have an impact on her access. They are not small branches. When is a good time to remove them, and how should we seal the cuts to prevent disease from entering the tree?”

You are very wise to ask before cutting, Rich — from now through the beginning of winter is the worst possible time to remove healthy branches from a tree, especially one as magnificent as a river birch! Pruning during the growing season always stimulates new growth. During summer’s heat, having to produce that ill-timed new flush of growth greatly stresses a tree.

Pruning in the fall is even worse as it prevents the tree from going into a natural dormancy.

The exception is heavily damaged, disease or dead wood. Those beat-up branches can — and should — be removed at any time. But removal of healthy limbs should only be done in the middle of winter — the dormant period when the tree is essentially asleep — or in the spring when the tree has just begun actively growing again and new growth is forming naturally.

Warning: If you try to remove a 100-pound branch all in one piece, it will swing around, smack you upside the head and break your shoelaces. It will also tear the bark directly below that branch section all the way to the ground. That’s why large branches should always be removed in manageable sections — a foot or so at a time.

When you are ready to make the final cut closest to the tree, locate the branch collar — the round structure were the branch meets the tree. You want to leave that collar on the tree when you remove the last of the branch. Don’t cut flush to the trunk.

Nothing should be used to seal the cuts. Nature knows how to do that much better than we do.


“I am shocked, shocked, to find mushrooms on wood mulch!”

Vicki and Danny in Rockville write, “All of a sudden we are having a huge problem with mushrooms around our shrubs, hostas, lilies and other plantings. The area is hardwood-mulched every year. Yes, we know that you say it’s bad, but we’ve done it for 15 years and this is the first time we have had a mushroom invasion. Is there anything we can apply to eliminate them? The scene out there is horrible!”

So, let’s see … you knew it was bad to use wood mulch, you kept using wood mulch anyway, something bad finally happened and now you’re surprised? The truth is that everyone who falls for wood mulch marketing will eventually get hit with a flush of mushrooms and/or other nuisance molds — some of which can cause severe (and expensive) cosmetic damage to homes and cars. Some people get hit with such problems the very first year they spread wood mulch, others get away with it for a decade or more. But sooner or later, the chickens — eh — fungal spores — will come home to roost.

For now, you can try spreading coffee grounds, lime or wood ash around the ‘shrooms to stop the spawning. Don’t yank them out. That spreads the spores.

Coffee grounds supply nitrogen, while lime and wood ash make the mulch more alkaline — both of which help inhibit fungal growth. But don’t use both — choose either grounds or wood ash/lime.

And of course, the long term answer is to switch to a mulch that isn’t attractive to rogue fungus such as compost, pine straw or pine fines.


Wood mulch = worms (but not the good kind)

WTOP 2014; bagworms
The images Dwight sent show a severe infestation of bagworms on an evergreen. (Courtesy Mike McGrath)

Dwight in Randallstown writes, “I recently changed my mulch to wood and now bugs have appeared; what are they and what should I do?”

The images Dwight sent show a severe infestation of bagworms on an evergreen. These clever caterpillars (every pest with the word “worm” in its common name is actually a caterpillar of some kind) live in small nests — or “bags” — that look a lot like the pine cones that naturally appear on the plants they attack. And so the “worms” often escape detection — sometimes even while they’re eating the evergreen to the ground.

Bagworms — and similar pests such as tent caterpillars and fall webworms — often appear in response to stress such as feeding with chemical fertilizers or — ahem — mulching with chipped-up pallets from China spray painted some God-awful color.

The initial answer to any caterpillar problem is to spray Bt on the plant. Sold under brand names such as Dipel, Thuracide and Green Step, this organic pesticide made from a naturally occurring soil bacteria only affects caterpillars that eat the sprayed parts of the plant. Bt harms nothing else. The “worms” will stop eating immediately and die shortly afterward.

In the long term, avoid using chemically-based plant foods and stop using mulches that stress your plants. Switch to compost or pine straw. A healthy, happy plant rarely suffers these kinds of attacks.


Rubber baby buggy mulch

When I sent Dwight in Randallstown my email advising him to get rid of the wood mulch that had made his plants so attractive to bagworms, his reply — and I could not make this up — was “Okay — so my next step is to go to black rubber mulch?”

Oy! I should have listened to my mother and taken that job in the fish canning factory back when I was 15!

No, no, no, Dwight. Black rubber mulch is made from chipped-up old car tires. It’s potentially toxic, a definite fire hazard and definitely stinks in the summer heat. Stop letting people with waste disposal problems use your landscape as a landfill, and switch to a mulch that prevents weeds without nasty side effects, like compost, pine straw or pine fines.


Artichokes: Let George do it!

John in Burke emailed me to say, “I have artichoke bushes that have gone through two winters now. They are very healthy looking and growing well, but I can’t seem to get them to produce actual artichokes. Any suggestions?”

I replied, “I realize that this is a punch line, but: ‘Gee, mister — I didn’t know that artichokes grew in Virginia!’ (ba-dump-bump; rimshot)”.

John countered with, “you see artichokes all over Mt. Vernon; that’s where I bought my seedlings.”

This is a great lesson in what experts can do when they have greenhouses, cold frames, hired help and lots of knowledge, John. Not to mention that Washington himself was immensely talented at getting plants to thrive outside their normal range. In other words, although artichokes can technically be grown in the mid-Atlantic, it is a laborious and involved two-year process that requires constant attention. It is not a “plant it and forget it” project.

I suggested that he contact the gardeners at Mt. Vernon to see what kind of tricks and techniques they use, as their advice would jibe perfectly with his own microclimate. Also, I sent him this article from the Connecticut Agriculture Extension Service that provides some solid advice on how to try growing artichokes outside of their normal range and an article I wrote on the topic for my Public Radio show some years back.

But, as I say in that article, there’s a darn good reason that virtually all American artichokes are grown in a single county in Southern California.

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