Here in the CONUS turfgrass transition zone (See my blog post on “Turfgrass Adaptation”.) the conditions are lousy for cool season turf and warm season turf.  It gets cold enough in the winter so warm season turfs go dormant.  And it gets hot enough in the summer so cool season turfs go dormant.  Its really NOT ideal for either type of turfgrass.  Living in the north, deep south or out west makes turfgrass cultivation and care a little easier.

This is the time of year when I get a lot of questions about how heat affects our turf.  Most of the time when there is heat stress on the turf there is also drought stress, and vice versa.  So I usually lump those two situations together.  But, first let me talk about heat stress.

As I’ve stated in other blog posts, the most favorable temperature for cool season grasses is 60 to 75 degrees F.  But, many turfgrass species vary in their tolerance of heat.  Perennial ryegrass, annual bluegrass and rough bluegrass will feel the effects of heat stress sooner (or at lower temperatures) than tall fescue.

I tell all my customers in the DC, MD & VA area to have tall fescue.  Tall fescue has the best high temperature stress tolerance than any of the other cool season grasses.  Depending on watering, it may go dormant in the middle of the summer.  That’s fine.  And it remains green all winter.  I like that.

I mentioned this in an earlier post as well – species selection is key when starting out.  Don’t plant warm season grasses in Wisconsin and don’t plant cool season grasses in Louisiana.  Ever wonder why you can’t get St. Augustine grass seed easily in your favorite garden center in Maine?  That’s because it won’t grow well there.  You’d be wasting your money…and the seed.  But, in the transition zone – sometimes those decisions are not that clear.

I will list below the cool season grasses in order of the most heat tolerant to the least heat tolerant:

Tall Fescue

Creeping Bentgrass

Kentucky Bluegrass

Red Fescue

Annual Ryegrass

Perennial Ryegrass

Annual Bluegrass

Rough Bluegrass

After species selection, two other important factors are soil moisture and air movement.  Keeping the soil moist and the air moving over the turf helps the turf cool itself, enhancing its own, natural transpirational cooling ability.  Ever see a nice golf course using fans on the surface? That’s what they are doing…helping the turf cool itself. 

Think about the concept of “evapotranspiration” or ET.  Not the movie about a little alien.  ET is the sum of evaporation and plant transpiration from the Earth's land and ocean surface to the atmosphere.  Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and bodies of water.  Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves.  Evapotranspiration is an important part of the water cycle.  An element (such as a lawn or tree) that contributes to evapotranspiration can be called an evapotranspirator.  This is how plants cool themselves.  Just like humans, if plants can’t cool themselves, bad things start to happen, usually resulting in death.

Now, above, I used the word “moist”.  Don’t be confused.  I mean moist for cooling purposes.  See my blog post on “Irrigation”.  Air flow has a distinct relationship with irrigation or watering.  Moist does not mean submerged.  Too much water, or having water pooled on your turf can result in disease.  If your water runs off, or puddles on the surface, you are applying to much….too quickly.

Another consideration is the landscaping around the managed turf area.  Are there things like plants, fences, or other “obstacles” that may block or minimize the movement of air over the turf area?  Air flow is important to all plants. 

I know this may conflict with other aesthetic or values based beliefs regarding landscaping.  One such conflict is “turf or trees”.  It is the never ending discussion between guys like me (a turfgrass warrior) and the arborists (tree huggers – literally).  Turf guys will have turf growing right up to the base of a tree.  The arborists will say that the turf is taking much needed nutrients from the trees.  The tree guys will say you have to have a mulched bed all the way around the tree out to each tree’s drip line.  Listen, if I had beds like that for every large tree on my property, I’d have no turf. 

Maybe I was digressing, but, I believe trees, shrubs and turf can coexist in complete harmony.  You just have to have a vision and you have to have an operations plan.  Hey, I fertilize my turf and I fertilize my trees and shrubs.  I cut my lawn and I prune my trees and shrubs.  I take care of them all.  Unfortunately, sometimes, you may have to make some tough decisions.  Those decisions are also sometimes based on funding, personal preferences, prioritization and what is best for the plants.  If you have to aggressively prune an area of trees and shrubs for your turfgrass – so be it.  And, God forbid, if you have to surrender a portion of your turf area because of densely planted trees or shrubs – that’s your call too.  Its a tradeoff.  (Surrender is not a frequently used term in my vocabulary.)

I will be discussing cold tolerance next.  And, another topic soon to follow is shade tolerance. This topic regarding the “conflict” between turf and trees also applies to dealing with shade.