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Weekly Gardening Guide: Barking up the Wrong Tree!

October 8, 2015



Barking up the wrong tree:

Hey folks, I hope you’re about to enjoy a wonderful Thanksgiving weekend with your friends and family. It sure looks like the weather is going to cooperate! Sarah and I will be joining our families for dinner on Friday and Sunday, and even hope to squeeze in a final round of golf before its time to hang up the sticks for the winter! It should be a lovely long weekend.

Of course, despite the warm temps, we all know what Thanksgiving means in Canada – The unofficial kick off to autumn, chilly temps and falling leaves…. Which inevitably means that winter is just around the corner.

I know. We don’t like to think about it. Especially gardeners, who must watch the fruits of their summer long labour get buried under the white stuff, not to be seen again until spring. I suspect several of the coming blogs will likely focus on preparing for winter, since as most green thumbs know – what you do to your gardens just before the snow flies, can have a major impact on the success or recovery of those gardens come spring time.

Today, we’re going to focus on those wascally wabbits…. And how those cute little fuzzy wuzzies can inflict BIG damage on your prized woody plants. I will be focussing namely on rabbits, but voles, mice, and other non-hibernating mammals can cause the same problems.

Unfortunately, at some time or another, most gardeners have rushed out to their gardens on the first warm day of spring excited to see DIRT again… only to find that tell-tale ring of teeth marks around your favourite ornamental. Be it a Japanese Maple, a Purple Leaf Sandcherry, or your newly planted Redbud, rabbits show no mercy when looking for fine dining in the wintertime when food is scarce.

While the commonly held belief is that rabbits eat the bark off your trees because they are desperate for food, that is not exactly true. If rabbits were really just “hungry for anything” they would gladly dine exclusively on evergreen bushes or other fleshy greens. If they were that desperate, they would likely choose to snack on the easily accessible branches of your shrubbery rather than digging into the snow to eat at the bark. In truth, while all summer rabbits prefer to eat leafy greens and will continue to do so throughout the winter – bark provides a certain concentrated nutrition that is unavailable to them from other parts of the plant. Only certain mammals are even capable of digesting the bark, cork, and vascular cambium layers of a plant, but those that can derive much nutrition and sustenance from the cellulose, pectin and lignin found in high concentrations in the dense bark tissues.

However, the bad news for the gardener is that bark is absolutely essential to the survival of a
woody plant. Bark is not just a “protective layer” as some misinformed folks may believe. While it is true that the outer bark of the tree protects the fleshy new growth and wood from being attacked by animals or insects, it is a bit more complex than that.

Bark is made up of several layers. The exterior-most layer is in fact simply called “outer-bark” and acts as a physical barrier to injury or attack from animals or insects. But the additional layers of what we commonly call “bark” are extremely important to the physiological function of the plant. The next layer (moving inward) is called the phloem. The phloem is a crucial part of the “sugar transport system” of a tree. Xylem moves sugar and energy up from the roots, and phloem moves harvested energy from the leaves down into the roots as well as moving nutrients as needed from “source to sink” – both up and down the tree. It is a vital part of the tree’s ability to acquire nutrients and move them around to the needed parts. The best way I can describe it is a vein (deoxygenated blood) vs. an artery (oxygenated blood). The heart moves freshly oxygenated blood from the lungs, pushes it throughout the body through our arteries, and as our body uses it, the deoxygenated blood returns to the heart and lungs via our veins (just an analogy, I’m a turf-guy not a doctor!). The whole system is complete ONLY when both “transport highways” are present. Without one or the other, we would die.

Unfortunately the same is true for the xylem and phloem of a tree. When the entire circumference of the bark is destroyed by a pest feeding or a weedeater getting too close the tree will eventually die – its blood supply has been cut off! The younger the tree is, the thinner it’s bark, and the more likely it is to be catastrophically injured by a ring around its bark. This is called “girdling” a tree. It can also happen by way of “choking” or suffocating when a root girdles the tree by wrapping itself around like a boa constrictor and cutting off the phloem supply of nutrients and sugars. Here’s a real life example of girlding that didn’t even involve a rabbit!

I grew up playing golf at River Road Golf Course – one of the city owned courses. I would later spend several years, including last year, working on their grounds crew. Anyone who played there prior to 2009 will remember #11, a short dogleg left par 5 whose main defence was a giant hickory in the middle of the fairway. And I mean GIANT. This tree was probably 75 feet tall, and it took a very accurate lay-up shot to leave yourself an angle at the green that wasn’t interfered by the tree.

It was always a controversial tree. Some people loved it for the challenge it provided, some people thought it was silly. Regardless it was there, and it made the hole what it was….. until one winter day, when the course was quiet and empty, some rogue cross country skier who was obviously also a disgruntled golfer, took it upon himself to take a small hatchet and chop a ring of bark all the way around the tree. The ring was maybe only 5” wide, and only about half an inch deep – but it was enough to completely sever the phloem connection between the roots of this giant hickory, and its aerial branching.

The tree only lasted 1 full season before it started dropping branches. It became a safety hazard and had to be cut down – to the cheers of many and the tears of few.

What I’m getting at here is – it doesn’t take much! A tree may be 75’ tall but its vital “organs” are contained within the first inch of its thickness. Those little bites from that cute little bunny are enough to kill a tree thousands of times its size.

But theres hope!

If, like us, you discover that say, a bunny has eaten 2/3 of the way around the bark of your BEAUTIFUL Japanese Maple, don’t arrange the tree funeral just yet. There’s still a chance. So long as there is some connection of healthy bark to complete the vascular network, the tree may still pull through. But you don’t (read: “Shouldn’t”) help it along. Don’t paint the wound. Don’t wrap it. Don’t pull out the voodoo dolls. Just let it be. Just continue to care for the tree the way you would any tree – fertilizer, water, pruning as needed. Alternatively, if the bark has been chewed 360 degrees around the plant, the tree or shrub may react the way that a shrub does when its pruned aggressively – by sending out a flush of new shoots from the base of the crown. This is small consolation if your tree was mature and established, but for some smaller shrubs, this may just be a convenient replacement that doesn’t need planting!

So – how can you prevent it!?

Well, since there is no *cure* for damaged phloem besides “wait and hope” the best offence is a good defence – prevent the rabbits (voles, mice) from feeding in the first place.

There are some products out there such as Plant Skydd, Scoot and Liquid Fence that are simply deterrents to feeding. They work by tasting or smelling bad, and hopefully prevent feeding from occurring. However, in my opinion they are less than ideal since they usually mean the rabbit has to gnaw a few chunks out of your tree before realizing he doesn’t like the sauce that you put on it.

So I suggest physical barriers such as chicken wire, drain tile, rubber hoses, etc. Anything strong enough to withstand cold and wind, and tall enough to block an outstretched and hungry rabbit (18”, or past the main trunk height). I don’t like to see these barriers to be left on all year, unless you have pest problems year round – or say a husband who gets a bit wild with the weedeater. A tree needs to breathe and grow without restriction, and the crown and bark tissue needs to be allowed to dry out after watering or rain, so don’t leave non-breathable barriers on all year.

In addition to wrapping the trunk, consider fences that are tall enough to completely keep pests out of the garden in the first place. This can be made as simply as some bird mesh stapled to a couple stakes in the ground, or you can roll out the snow fence. Just remember, a foot of snow shrinks your fences by a foot – rabbits are good climbers! So make sure your fencing or netting is tall enough for our typical snow fall  (24-30”). Whatever you need to do to stop them from getting into the garden, since they will also feed on the buds of woody shrubs, and as mentioned earlier some of the fleshier evergreens (euonymus is a favourite).

One more home remedy you can try is to mix up a water based mixture of various capsaicin containing pepper powders – the hot ones! – this includes jalepeno, cayenne, chilli powder, etc. There are lots of recipes online, but the important thing to know is that rabbits don’t like the smell or taste of hot pepper. So a simple squirt bottle solution sprayed around the perimeter, and on the bark of your favourite woody plants might act as a second line of defence in addition to trunk wrapping.

Unfortunately, we must attempt to live in harmony with our animal brothers and sisters, since they are everywhere! But living in  harmony doesn’t mean we can’t protect our stuff! Hopefully this information can be useful to you in preventing future rodent dinners this coming winter.

As always if you have any questions or concerns feel free to email, call or stop into the store!
Happy gardening,

Bryan

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