The Heat is On! Which plants can survive a hot, dry Tennessee summer?

Pineapple Sage (Salvia elegans), not so drought-tolerant after all

The other night, I heard that nearby Franklin, Tennessee has started requesting voluntary water conservation from its citizens.

There hasn't been much news about the drought yet (despite the fact that Tennessee's rivers are at or near historic lows this year), but I can tell you that it is hot and dry.

We're talking mid-90s Fahrenheit (~35 Celsius) every day with high pressure parked over the region and no rain in sight.

Lawns up and down the street are turning brown, despite the fact that most people are watering daily. (I find lawn watering awfully wasteful, so I use our irrigation system a few days a week and feel guilty even using it that much. So our lawn is browner than most.)

But I don't care much about lawns. If I could afford it, if our HOA would allow it and if I thought it wouldn't adversely affect retail value, I'd rip it all out and replace it with landscaping with greater ornamental value and greater wildlife value for bees, butterflies, birds and other critters.

But that raises the pertinent question of what plants can survive the extremes of a mid-Tennessee summer. And I can tell you right now that it's not looking pretty.

Take the Pineapple Sage (Salvia elegans) at the top of this post. I thought this was supposed to be heat and drought tolerant, full sun plant. Apparently, I was misinformed. On closer research today, I discovered from Floridata that pineapple sage needs regular watering for best growth and flowering. Apparently it can sometimes survive a drought by wilting and dropping its leaves, but it won't thrive in drought conditions.

(Floridata also says that pineapple sage is best suited for zones 9-11, so I really goofed when I bought the plant for my zone 7 garden!)

What about zinnia? The University of Florida extension service describes zinnias as being a drought-tolerant annual. Floridata (one of my favorite information sources, despite the fact that I don't live or garden in Florida) describes zinnias as being "quite drought tolerant" plants that do best in full sun. The plant shown below must not have gotten the memo, as it is looking cooked. (I will note that now that I am scouring plant descriptions specifically looking for drought tolerance, I notice that many merchants, such as Burpee, emphasize that zinnias are heat tolerant without mentioning drought tolerance. Maybe zinnias are moderately drought tolerant, but do better in hot and wet places?)

Zinnia

How about Russian Sage? As you can see below, the plants are still rocking away and producing a profusion of blooms that attract a happy chorus of buzzing bees all day long.

Russian Sage (Perovskia atriplicifolia)

And yet, the picture isn't quite as pretty just a bit further down each plant where the leaves are yellowing, browning, turning yellow and falling off. What's the reason? Various Internet sources suggest either (a) too much water, (b) too little water or (c) shedding leaves as normal behavior. The mighty Missouri Botanical Garden says that Russian Sage (Perovskia atriplicifolia) tolerates clay soil, dry soil and drought, which pretty much precisely describes its environment. And yet, there's no mention of yellowing leaves...

Russian Sage (Perovskia atriplicifolia), yellowing leaves

Well, let's not make this post all doom and gloom! The good news is that after weeks of teasing with nothing but foliage, the French Marigolds (Tagetes patula) have started to burst into bloom. True, the 'Sparky Mix' seeds I bought from EverWilde were supposed to grow into plants 12-inches tall, whereas the actual plants are less than half that height, but the flowers are endearingly luminous.

French Marigold (Tagetes patula)

Some of the leaves Natchez crape myrtles are looking a little limp, but the trees themselves are covered in blooms. I think we have many more flowers this year than last year.

Natchez Crape Myrtle

And Purple Cone Flower (Echinacea purpurea) is still going strong, to the delight of bees and butterflies. (At least, I think these are butterflies, operating on the layman's assumption that moths land with wings flat and butterflies fold their wings...) University of Maryland's Cooperative Extension describes purple cone flower as "quite drought tolerant," while University of Delaware's Extension service describes Echinacea purpurea as being "very drought resistant." Interestingly, definitions of drought tolerance may differ here in the U.S. versus across the pond in Europe. I found one U.K. site that says Echinacea needs water at least weekly in full sun. I'm guessing that is the case, as a couple of my Echinacea are looking a little drought-stressed (though they're still getting by much better than the pineapple sage or the zinnia). Perhaps in very hot areas with drought risk it makes sense to ignore the usual full sun recommendation and plant Echinacea where it will get some afternoon shade?

Echincea purpurea, standing tall for now despite the drought

We have four or five of the Natchez crape myrtles in full sun, as well as an unidentified lavender crape myrtle that gets less morning sun, though it does get plenty of solar radiation in the afternoon. This specimen is thriving, growing vigorously and not exhibiting any signs of drought stress. Of course, it also has hardly any flowers at this point, but the one bunch of lavender flowers that has opened looks lovely and has a light, sweet fragrance.

Lavender crape myrtle flowers

 Over to the front of the house (morning sun, afternoon shade), we find that Calycanthus floridus, also known as Carolina allspice or sweetshrub. Floridata says that Calycanthus likes moist soils, but can survive drought. I've been giving the plant a deep watering twice a week and so far it seems to be limping along with just a bit of leaf tip browning. The plant is native to the Southeastern U.S. and is supposed to have fragrant spring flowers. Obviously no flowers this year as this tiny plant (purchased through mail order) is just getting established, but I'm hoping I can nurture it through the drought so that I can enjoy its flowers next spring.

Calycanthus floridus, Carolina allspice, sweetshrub

Last but not least, here's a look at an Ajuga reptans that seems to have happily established itself in one of the shadier corners at the front of house. North Carolina State University (NCSU) includes ajuga on its list of drought tolerant plants, and this specimen certainly seems to be living up to its reputation, perhaps helped by the fact that it gets shade from about 10 a.m. onwards. It's not a particularly flashy plant, but I've definitely come to appreciate ajuga's shiny, classy foliage. I'm hoping it spreads into a sizeable groundcover, and I suspect that next year I'll be able to enjoy more of its blue flower spikes.

Ajuga reptans

That's all for now. I didn't include any photos (to keep this post at a somewhat manageable size) but I can tell you that the Autumn Joy sedum and the phlox paniculata (shown in the June 21) post are both doing fine. Both sedum and the phlox are on the NCSU list of drought-tolerant plants.

The drought has struck harder and earlier than usual in Tennessee, but we're certainly no stranger to droughts here and this experience has only reinforced my feelings on the importance of planting drought-tolerant or drought-resistant plants in any climate that is prone to water shortages. It seems to me this makes sense for two reasons: (1) You may enjoy watering (I do), but it's nice to know that your plants can survive for an extended period of time if circumstances prevent you from watering for one reason or another, and (2) with 300+ million people in the U.S. and 7+ billion people around the world, planting a landscape that needs lots and lots of supplemental water doesn't seem like such a swell idea.


Dear readers, I'd like to get your thoughts on a few questions:

1. Is your garden facing drought now or have you faced drought recently?

2. If you've encountered drought in your garden (now or in the past), what have turned out to be the toughest and most drought-tolerant plants in your experience?

3. How do you define drought-tolerant? Is a drought-tolerant plant in your garden one that only needs water once a week? Once a month? Never needs any supplemental water?

Thanks for reading! And let's hope for rain -- 'cause it's a good thing!

PS - Curious as to what's going on in the veggie garden? Check back in a couple of days for an update on the tomatoes, cucumber, pole beans, okra and more!