This is a stretch, but has anyone had any luck specifying a turfgrass blend on a greenroof? The catch is that it will have (at best) 3" of soil.

This is not ideal in any situation as it is, a-monoculture and b-irrigation hog, however it is only a small portion of the extensive roof so we may be able to create a micro climate of sorts for it to exist in.

Anyone have any thoughts?

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As a horticulturist, I must urge you to recognize that plant selection is site specific. You must consider what region you are in, what sun/light levels and wind is like at the site, how the turf area will be used, cool season? warm season? blend? Light weight planter mix or actual soil mix?

3" "soil" will not produce a usable lawn (one short party will kill it), but if it is a visual feature only, then there may be possibilities (depending on where you are building it).

Thanks Rob. I can assure you that there has been a tremendous amount of time that has gone into species selection on this project. The building is approximately 1 acre with over 30 terraces - each having a very different microclimate from the next.

We are not thrilled with the idea of using turf to begin with, however the client has asked we substitute out extensive greenroof (sedums, etc.) for turf in select areas. These areas account for approx. 5% fo the overall footprint - a reasonable enough request considering over 50% of the footprint is greenroof.

The problem is exactly as you stated - we do not have the soil depth to grow a usable lawn! The project is in NYC, any recommendations would be welcome.

Thanks again!

Sounds like a lot of watering and feeding I have not done so, but it is done.

I'd go with synthetic turf on a roof like that. You just don't have the soil depth for proper root growth. If this was in Florida, you may have been able to use a bermuda with very heavy maintenance and replacement schedules. You can try a creeping bentgrass (Agrostis stolonifera) that is used on golf course putting greens. It is a cool season grass and will grow in NYC when planted in a sandy soil matrix, again, like on putting greens. Both require insane amounts of maintenace, constant mowing and rolling (almost daily), lots of irrigation, and regular replacement of the turf as it easily browns-out and wears down with use. Both of these grasses are what they use in customized thin growing medium on cruise ships depending on where they sail. The issue is obviously weight. To properly grow turn, you will need to approach intensive weight and semi-intensive depth to properly support turf. Thats why I'd go the synthetic route. Good luck.  

Thanks Jason, this is really helpful. I've since found ways to "increase" the soil depth to about 5". So there's a small silver lining there.

As for synthetic, yeah, thats what many others have recommended as well. Problem is we have to hit a certain percentage for vegetated roof coverage. I've been looking into slow growing and hard fescues. Haven't found a blend yet, but still in the hunt.

Any suggestions are always welcome!

Look into this stuff. It is a rhizomatic low-growing variety of bluegrass. It only grows to 2" or 3" meaning low/no mowing and since it is rhizomatic, it self-heals and needs much less watering. And since I first spotted it, they seem to have a deal with LiveRoof to make it into green roof modules, which makes the whole operation that much easier. The question I would have for LiveRoof is if the turf can be used like a typical lawn. If you are doing a loose-laid green roof, you can order this also as either sod or plugs. You might have to get it from the Carolinas or Florida. I know the sod farms here won't grow it because it takes a while to grow, tying up their fields for their typically crappy fescues, and you grow it with sprigs rather than seed, which is a more intensive operation. If you do end up using it, I'd love to track the results.

http://www.bellabluegrass.com/roof.php

www.bellabluegrass.com

Thanks again, I certainly will look into this. The initial thought was to hydroseed the area, however sprigs could be an interesting alternative. I'll see if its rated for traffic. If anything good comes out of this I will let you know. 

Thanks again!

Have you ever been near a synthetic grass that has full sun exposure on a hot day ?

You mention "soil"...what's the mix ?    Does it break down over time ?  What is your irrigation ?

If the potential is a boggy situation in time, then go with somethng that grows in boggy situations.  Investigate what grows streamside and in wetlands where your project is and see if it is commercially available as plugs. 

Here on the west coast, we have Carex, of which many species will grow in thin soil and boggy situations.  http://en.wikipedia.org/wiki/Carex  I've seen C. pansa grow nicely in poorly drained low spots of lawns.  Maintenance wise, it was always green and it never grew tall enough to get cut by the mower.

Check http://en.wikipedia.org/wiki/Cyperaceae for sedges that might be in your area.

Remember that most not all green roofs are essentially alpine gardens. Full sun, lean soil, potentially limited water, windswept, etc. There are turf species that do well in that situation and as you stated fescues are one that will work.

Bingo. We've been investigating grasses that are tolerant of desiccation, full/part sun and resilient.

Havent found the right mix yet, but we're in the hunt.

The situation is definitely not boggy - the opposite in fact. We are using a proprietary soil blend created for green roof plantings so I'd have to do a bit of research to see if it breaks down over a given amount of time. 

We are already specifying  a significant amount of sedges on the project, this particular area calls for something that can withstand foot traffic and the occasional lounge chair.

Thanks for the links though.

Since the area will be receiving some foot traffic, lounge chairs etc…It seems that maybe a grass paver type application may be applicable. If there is a light weight grass pave system you could use with the correct grass, that may be a solution. The pavers may take some of the abuse away from the grass. But… you will likely run out of growing/paving section pretty fast with your 3-5”.

Could you do a raised  walkway and seating area to gain a bit more section for your grass?

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