8/3/2019 Putting the Green in Green Roof

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Midwest Values Business Resources Networking0

DaveMacKenziefoundedHortech,Inc,inSpring

Lake, MI, a wholesale nursery specializing inlow-maintenance, water-conserving turf alternatives

in 1983. In 2006 Hortech started LiveRoof, LLC, as ahorticultural science company to design and manu-

facture a more innovative, plant-friendly system forgreen roofs. Dave answers some fundemental ques-tions forMidwest Roofer.

How dd yo e o ree roos?

Hortech started supplying plants or green roos in the 1990s. It was2003 when we got into the business in a very big way as a supplier andconsultant or Ford on their huge green roo in Dearborn, MI. At aboutthat time, a contractor to whom wed been supplying plants asked i Iwould drive over to Chicago to help out with problems on some green

roo projects. When I looked at all the problems the contractor wasdealing with, I thought to mysel, I could do better. In 2006 we startedLiveRoo to do just that.

Wh re he problems o hose ree roos?

Its more a question o what wasnt a problem. The choice o plantswasnt appropriate or the tough environment o the rootop, the waythe plants were planted was ar rom ideal, the soil in which the plantswere planted was wrong, and the design o the modular trays wasntplant-riendly. I realized all these issues had one root cause: No one wasseeing the rootop as an entire biologicalsystem. Green roos have to bemore than just separate trays o plants set out on a roo or a vegetativemat rolled out on a roo. A green roo has to begreena unifed,

horticulturally sound, sustainable ecosystem in which plants can thrive.

So he ree roos were o horclrlly correc?

Exactly. The one essential point I should communicate to rooers is this:Plants are living things with biological requirements that nature wontlet us ignore. Wherever plants are planted, they have to be right or theenvironment, and the environment has to be right or the plants. Weneed to understand that, just as the structure o a roo has engineeringrequirements, a green roo has horticultural requirements.

is he sol prmrly orc or orc?

The growing medium or some green roo systems is lightweight andconsists o mostly organic material with lots o compost and peat. But this

sort o soil tends to shrink in volume, decompose, and wash away. Based onsoil science, the growing medium or green roos ought to be more than90% inorganic material by dry weight, supplemented by a small amount odisease-suppressive organic material.

are ve pls ood or ree roos?

This would seem to make sense intuitively, but its not really true. Theplants that thrive on a green roo are drought-resistant because they areexceptional water conservers without deep root systems. That rules outmost native plants. Succulent, water-holding plants like sedums andalliums are well-suited to any rootop environment.

Why re prre pls kow or droh

ressce?

Plants like purple cone ower and prairie dock are very drought-

resistant, but it is not because they are water conservers. They are whatwe horticulturalists call water sourcersa class o plants with wide-ranging root systems that can go as deep as eight eet down in search owater. Extensive green roos have soil depth o six inches or less. Watersourcers arent right or the rootop environment and wont survive orlong on an extensive green roo without regular irrigation.

Whch bes he qeso: to rre or o o rre?

Assuming proper plant selection, supplemental irrigation is seldom neces-sary; however, a backup irrigation system or prolonged hot, dry, windyweather is a good idea. In addition, a little bit o irrigationor instance,just one inch per month during the hot seasonis usually sufcient tokeep plants hydrated, plump, and thick. That minimizes the opportunity

or weed encroachment and lowers maintenance costs.

theres b debe he dsry over rowpls rom pls verss cs. Whs hederece?

A plug is like a single starter plant in a disposable plastic containerrom a garden center. Several plugs are plugged into soil in a modulartray. A plug-planted system is a set o trays each with rows o individualplugs. The area each plug covers is a monoculture o one variety. Inseason, the plants may look good but in dormancy, not so good. Sinceplugs are plugged in rows, you end up with rows that dont look good

when deciduous plants drop their leaves during dormancy.Starting rom cuttings, you can establish an intermingled blend odeciduous, semi-evergreen, and evergreen plants. When modules o plantsrom cuttings are installed, the green roo looks like a meadow and staysbeautiul throughout the year. When the deciduous plants go dormant, theyare hidden amongst the others. Starting rom cuttings, a green roo can goup with ull-grown, ully mature plants; with plugs, it can take 2 or 3 yearor the plants to grow.

Putting tHE gREEn in gREEn ROOfS:

Q&A with LiveRoofs Dave MacKenzie