Overwintering an outdoor Zone 6 vertical garden

Boxwood and Heuchera 'Hercules' late November

Admittedly, this may be an answer to a question that no one has asked, but after four years of tinkering, I think vertical gardens (or vg's) can and should be a component of a zone 6 landscape design.

The first step in creating a vertical garden that will overwinter in Zone 6 is thoughtful plant selection.

I approach outdoor vg plant selection the same way I select for a standard planting composition: a combination of zone hardy, herbaceous and evergreen perennials and shrubs.

Boise may not get tremendously cold, but the dull, flat grey light of winter seems indeterminable as it drags into early "spring". As a countermeasure to the winter blahs, I make it a rule that at least half the plants I've chosen need to contribute winter interest either though dormant foliage (Pennisetum, Echinacea etc.), or evergreen or semi-evergreen foliage (Heuchera, Lamium, Hellebore, etc.). Hostas , for example, are terrific in the growing season, but they offer little in the way for winter interest.

As any gardener worth their Felcos knows, you need to select zone appropriate plants for your growing region. In horizontal applications, you have a little wiggle room; I've had pretty good luck with Zone 7 Black Mondo grass for instance. In a vertical application, you're better off sticking with a plant that is actually a zone or two hardier than what you'd normally choose.

Evergreen/semi-evergreen plants that have done well for me in a vg application include:

Boxwood (Buxus microphylla var. koreana 'Wintergreen")
Heuchera (quite a range of hardiness among the new cultivars. 'Stormy Seas' and 'Hercules' do very well.)
Winter Creeper (Euonymus fortunei)

The second (and equally important) step for successfully overwintering a vertical garden in our  Zone 6 is scheduling consistent, weekly irrigation through the winter.

Winter desiccation can be a little rough on a high desert garden but can wipe out even the toughest plants in a vertical garden.  A vg can't take advantage of winter precipitation without sophisticated rooftop water harvesting (more on that another time), so you're left to puzzle out how to get water to your vg long after your sprinklers have been winterized.

The solution I've come up with for the time being is to "t" off the 1/4" line to our ice maker behind the fridge. Once a week, if the outside temperature is at least five degrees above freezing,  I run 50' of 1/4" line out to our vg's and irrigate for about five minutes.

Oh, and try to remember to make sure the irrigation lines on your vg are free draining and no longer connected to your outside irrigation system. Frozen, busted irrigation pipes and fittings can really take the fun out of vertical gardening. Good luck...









UPDATE 12-3-13

January 2013 ended up being the 5th coldest in Boise since 1865, with temperatures 10-24 degrees lower than average. Needless to say, irrigating our vertical gardens was a bit challenging. Most of the Heuchera and the Hostas woke back up in the spring, but we lost many of our newly planted Boxwoods from the unrelenting and extremely dry cold (lack of a developed root system?).

A typical winter in Boise isn't nearly as extreme, and with occasional irrigation this is what you can typically expect over the course of 10 months:

The first photo shows the vg module in all its late summer glory: Heucheras, Hostas, Winter Creeper Euonymus, Lamium and a single Blue Star Juniper.

After a couple hard freezes in November, the herbaceous Hostas turn to jelly but the rest of the plants still look pretty good. By February though, everything but the Euonymous starts to look pretty tired and mopey (a pretty accurate description of myself in late winter).

Finally, as our northern hemisphere leans forward again to the warmth of the sun, the vertical garden comes back to life.

This year I've been working on selecting tough natives and climate adapted species that could survive through the winter with little or no care. In May I was commissioned to build my first "xeric" vertical garden.

The first pic shows the wall right after it was installed at the end of May. The second shows growth after the first six weeks. 

Hemerocallis, Nepeta, Artemisia, Yucca, Sedum and Stachys byzantina 'Helene Von Stein'.

         
Stay tuned as I'll be posting a mid-winter update to show how the vg is holding up.

Vertical garden construction at OEC

Our latest vertical gardening project is for OEC, a Boise company committed to creating dynamic, innovative and effective work spaces. Here's a mockup of how the two sided vg will look mounted to their entry desk partition:

This is the first entry of two that will photo-document the entire construction process.

Step One: Cut mineral wool batts for the 28 square foot, two sided vg

Step Two: Drill the bracket that will be used to attach the vg to the 5x5 partition post

Step Three: Attach the bracket to the 7/16 OSB vg armature

Step Four: trim bracket bolts

Step Five: Attach waterproofing vapor barrier to OSB

Step Six: Drill for 5/16 double sided mounting screws

Step Seven: Attach bolts, carriage washers and nuts

Step Ten: Carve out inclined planting chambers

Step Eleven:  Fabricate 109 emitter T's

Step Twelve: Sharpen goof plug at the base of each emitter T

Step Thirteen:  Plunge emitters into the mineral wool batts above each planting chamber

Step Fourteen: Attach transfer tubing

Step Fifteen:  Insulative Mineral Wool insulation to the attic!

Step Sixteen: Use wood glue and loose mineral wool to seal seams between batts

Step Seventeen:  Use hot glue gun to seal emitters

NEXT: Completing the OEC vertical garden...

Rare and Historic Trees

Thanks to all who weighed in for our Locate this Tree contest. This Sugar Maple is located on 8th and O’Farrell and is one of 23 trees that were included in the Boise Park System’s last (and out of print)  Rare and Historic Tree pamphlet from 1989.

We set out a few weeks ago to find how many of these trees are still with us and were pleased to find that most of the trees included in the Rare and Historic Tree pamphlet are still standing. The Sugar Maple, which will begin to dazzle us with its brilliant fall foliage in a few weeks, has recently been heavily impacted by well meaning but potentially damaging hardscape installation and incorrect pruning. The concrete patio around the base was installed at the expense of the tree’s shallow, fibrous roots which were doubtless cut and compressed for the patio base.

I’m also concerned with the recent conversion to micro-irrigation, which again, may be well intended, but probably won’t provide the broad, deep watering the tree prefers. The Perma-Bark “mulch” is also a poor choice as the rock heats up the soil and has zero water retaining capacity (find my earlier diatribe against the material here).

Finally, the pruning has been done in such a way that the tree will have a hard time healing over the wound. Proper pruning cuts need to be performed at the point where the bark branch collar terminates at the branch. This allows the cambium to quickly heal over the wound. An open, unhealed wound can become a conduit for disease and decay.

This isn't the first time this old tree has suffered abuse. The north side of the canopy has been repeatedly butchered for utility lines. We're hoping the tree takes this new round of assaults with grace and patience.

We’re committed to raising awareness of the many “heirloom” trees throughout Boise in effort to see that they are given proper care so they might be enjoyed by future generations. Stay tuned as we share some of the original trees nominated for the Rare and Historic Trees pamphlet and introduce a few notable others we've found. Contact us if you have trees that you’d like to see on this expanded list.

Vertical Gardening in Boise

In anticipation of my conversation with Charlie Woodruff of Building a Greener Idaho tomorrow on KRBX 89.9 FM, Radio Boise, I thought I'd post a series of pictures showing some of the vertical gardens we've built over the last few years. Enjoy!



Tropical Vertical Garden at Edward's Greenhouse in Boise, Idaho

Rosemary and Thyme Vertical Herb Garden

Vertical Garden on our Chicken Coop

Hosta and Heuchera Shade Vertical garden

"Industrial" Vertical garden for Lulu's Pizza

Our Office Vertical Garden

Vertical Garden Framed in Barn Wood

Lightweight Vertical Garden Module

On Display in Garden #6 of the Idaho Botanical Garden 2012 Garden Tour
(Thanks to Joanne Lechner and family!)

Perma-Bark

I'm certain Dante missed a circle of Hell where wicked gardeners are forced to pick detritus out of an endless bed of PERMA-BARK®.  I got a head start on this today as I attempted to remove pine needles, leaves & strands of ornamental grass mysteriously threaded into the crushed basalt. I rate the use of this awful material in garden beds right up there with installing lead pipes for potable water & staring unblinking at the sun for pleasure.

And forget about amending the soil in your beds; once the rock "mulch" is installed, you're left with a material that dramatically heats up the ground in the summer sun, offers little in the way of water retention in the growing season or insulative protection for roots in the winter and slowly chokes the life out of trees and shrubs.

Reason enough for eternal damnation.

Just leave the damn tree alone.

Balancing myself up in the canopy of a sturdy white oak earlier this week, it occurred to me how closely arbiter and arborist are in meaning as well as spelling. In addition to the inevitable landscaping disagreements between spouses that I'm often expected to resolve, my primary job as an arborist is to somehow reconcile what the homeowner wants with what the tree wants. The homeowner wants PRUNING, and the tree, well, it just wants to be let alone.

People get it in their heads that the tree is just standing there in immobilized agony wishing it could communicate it's desire for copious pruning. Not only does the tree not want to be bothered with your surgical urgings, it'll probably flip you some serious attitude. I call it "panic epicormic sprouting" and I have personal experience. I've carefully cut off branches and have been rewarded with the emergence of five or six new branches in the same spot to deal with. That's tree attitude.

Some tree "experts" have turned this into a pretty profitable business plan. They come over to your property and prune the living hell out of the interior of your tree. Nice and tidy (arborists call this kind of damaging pruning "lion tailing"- get the visual picture?). Lucky for the "experts", the tree freaks and pushes out twice as much growth to compensate the following season.

Call it job security. Beware of the tree company that charges by the branch.

Mature trees need occasional maintenance pruning. The 5 d's are often presented as reasons to prune anytime:

1. Damaged

2. Diseased

3. Deformed

4. Dangerous

5. Dying

Prune your trees when they are young to create good structure and shape (a future blog post), but leave your mature trees unmolested by your good intentions.