Protecting mature trees in a xeriscape conversion

Xericoasis would be a pretty stupid blog title if I wasn't at least casually interested in water conservation and zone sensitive landscape design. But the truth is, I'm getting increasingly annoyed at what I see as a "kill a tree, save the planet" attitude in a lot of xericape conversions.

It happens all the time in the urban forest of Boise's North End. Somebody decides that the Kentucky Blue grass in the front yard is sucking up too much water to be sustainable. Fair enough. But then they cap off the sprinkler system, rototill and remove the grass, install weed fabric and spread (God forbid) six yards of perma-bark over the whole area. They finish off the conversion by planting a handful of weedy looking natives and run single drip emitters to each plant.

I usually come on to the scene three to five years later when the eighty year old shade tree in their front yard starts dropping dead branches on the roof and they want an arborist to tell them why...

stressed tree in parking lot "xeriscape"

Tack isn't one of my strongest personality traits, but I do my best to politely explain to the client that:

1. the rototiller destroyed a large amount of the tree's fine water absorbing roots
2. the "perma-bark" superheats the soil
3. the weed fabric creates a hydrophobic dead zone, and,
4, the minuscule amount of water the drip line provides might keep a one gallon Eriogonum alive, but it won't do much for a tree that receives 30-60" of rainfall in its native range

Invariably, I hear the comment that that , "well maybe we shouldn't plant shade trees in our climate". Horse Puckey, I say. The benefits of our urban forest and it's role in such things as mitigating the urban heat island effect is well worth the investment of water it takes to sustain it. Besides, many properties in and around Boise are blessed with abundant non-potable irrigation water- a vestige of our valley's agrarian heritage.

Poor water coverage often seen in drip irrigation  systems

In Willowglenn installations, we often forego drip systems for a high efficiency broadcast sprinkler like Hunter's MP rotator nozzle. Efficient broadcast sprinklers more closely emulate natural rainfall, and encourage lateral root development. I've seen too many trees blown over because some genius thought that putting a bubbler at the base of tree was sufficient. It may keep the tree alive for awhile but it never develops decent lateral roots that would give it stability in the wind.

Integrating existing shade trees into a xericscape conversion can be done, but you have to be smart about it. The fact is, that 80 year old shade tree might have done OK hanging out with the turf grass, but turf grass and trees actually have quite different irrigation needs. Turf grass requires frequent watering but most trees prefer infrequent deep watering- a great starting point for the design of a mildly xeric design.

Choose an organic mulch and plant your xeriscape bed with a range of plants that provide four season interest. Take care to try and not damage the roots of your existing tree as you plant the shrubs and perennials and keep an eye on the tree for signs of stress.

How's this for an idea: let's keep our trees and save the planet. Brilliant.

Hazard pruning followup

Back in March of last year I wrote about the need for restraint when pruning mature trees. Hazard pruning is one instance where pruning a mature tree may be acceptable. Reasons for pruning might include: 

- pruning for road clearance 

- pruning away from roof shingles

- pruning away from chimneys

I was taking Christmas lights out of an enormous Rose of Sharon shrub last week when I snapped this picture of a maple tree that had been pruned for chimney clearance.

All three pruning cuts had been performed correctly and were almost entirely healed over. Looking closely though, you can see that in two out of the three branch removals, the tree has responded by sending out several epicormic shoots near each cut. Epicormic shoots lie dormant and are hormonally kept in check until damage or removal of a branch or leader occurs.

 Here's a closer look:

The first pruning cut healed over without any development of epicormic sprouting. The other two cuts have several new shoots apiece, growing right back towards the chimney, quadrupling the previous hazard.

So what's the take away? Don't forget to occasionally look up to see how the tree is reacting to pruning. Correctly pruning a tree is often not a one time event, but may need to be done over the course of several years. 


No shade tree? Blame not the sun, but yourself 
( Chinese proverb)

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.