Sunday, April 6, 2014

Evidence of Poor Drainage

A photo is worth 1000 words:

Poor drainage: water fills a hole in the garden more than 12 hours after a heavy rainfall
More than 12 hours after a heavy rainfall...

Digging a hole and filling it with water to check how quickly the soil drains is considered a standard way to check whether you have soil compact and poor soil drainage.

I didn't intentionally dig this hole to check soil drainage. I dug it in the process or removing an Euonymous alata (a.k.a. Burning Bush), which is listed by the National Park Service as an invasive plant.

I haven't quite gotten around to figuring out what I want to plant there, but whatever it is, it had better be comfortable with periodic flooding.

I already knew the soil drainage was not great in large parts of the backyard. The yard is sloped downward toward the street in the front, so the drainage is better there, but after heavy rains, parts of the back yard can stay soggy for days. When I hired a landscaper to add some plants to the back yard this year, he showed me just how compacted and dense the soil is back there.

I believe that the problem, as in many relatively new developments, has to do with soil compaction caused by heavy machinery. Plus I imagine that the top soil may have been scraped away to sell early in the construction process, with only a thin layer of soil (probably attached to the grass sod) put down when construction was complete. I can tell you there's about a half-inch of black soil attached to the grass in the backyard and then it's heavy, sticky, thick, murderous clay as far down as you can dig.

Thus the subtitle of this blog - Adventures in Gardening on Tennessee Clay!

That being said, the drainage is not equally bad everywhere in the backyard. Perhaps 30 feet away from the hole above, I dug another hole (while removing another burning bush). As you can see below, that hole did not hold water for nearly as long after the same storms had rolled through.

Clay soil with better drainage does not hold puddles more than 12 hours after a storm
Not nearly as much water in this hole, although quite a bit of mulch has washed in

So what's the problem with poor drainage? Roots need water, but they also need oxygen. Yes, roots need to breathe! If soil stays saturated for lengths of time, roots can drown and/or rot.

There are plants that can survive in wet or continuously moist soil, but they are not usually the same plants that are able to survive drought, which is also a regular occurrence in Tennessee.

Similarly, many drought-tolerant plants require well-drained, sandy or rocky low-fertility soils, which are clearly not the prevalent conditions here.

I'm compiling a list of plants that can survive both drought and flooding (plus single-digit winter lows and above-100 summertime highs). For instance, Baptisia australis (False Indigo) reportedly can withstand both severe drought and extended flooding.

I'd love to have suggestions to add to the list!

Comments (15)

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Hi, Aaron!!!! I have a spot in my garden that is like that . I don't plant anything there. SO annoying. I've tried everything over the years to improve the drainage to no avail.
1 reply · active 571 weeks ago
Thanks for the comment, Audra.

I suppose that is one solution - leave it bare! LOL!

Perhaps I'm foolish (is that really in doubt?) but I think I'll try some of those *supposedly* drought/flood tolerant plants and see what happens. If that fails, I suppose I could just fill in the hole and "plant" a birdbath or sculpture there! ;-)
Hi Aaron, I can vouch for yaupon holly! It has survived drought, torrential rains, high heat and bitter cold. Mine once had three feet of snow dumped on them and were completely buried. It is a native evergreen shrub that looks a lot like boxwood. Your list should be quite valuable!

By the way, you asked me about the shrub in my photo. It is upright rosemary. The one in the distance with the pink flowers is azalea. The 'wooden owl' you mentioned is actually a ceramic birdhouse with two little birds perched on top!
1 reply · active 571 weeks ago
Hi Deb,

Thanks for your suggestion. If I lived in zone 7b or warmer, I'd jump at the Yaupon Holly suggestion! But I've heard it can suffer damage at around 5-7 degrees Fahrenheit, and our temps regularly get colder than that here in 7a/6b. The low this past (unusually cold) winter was negative 2.

Now if I'm wrong (it wouldn't be the first time) and anyone has first-hand experience of Yaupon surviving (and thriving) in the colder parts of 7a, I'd love to hear about it!

The rosemary looks *gorgeous*. It's another plant I'd love to grow, but I've heard has a hard time surviving in our zone. I guess the "Arp" variety is supposed to be tough enough to take zone 7 winters, but again requires good drainage (or so I've heard).

It's a little known fact that wooden owls and ceramic birdhouses look kinda similar in blog photos ;-)
That is a telling picture. I have hard clay in areas, too (another victim of topsoil being scraped off during construction). Good luck with your search. I wonder if Louisiana irises would work for you. I'm trying them this year myself in a difficult spot.
1 reply · active 571 weeks ago
Thanks for the suggestion, but it *seems* as if Louisiana irises need consistent moisture, whereas I need something that can tolerate both drought and flood. http://davesgarden.com/guides/pf/go/33052/#b

I know I'm asking alot of a plant!
We have a couple of Burning Bushes that we should probably take out. They're such beautirul shrubs in the fall. I always feel so terrible about pulling out healthy plants, but I guess it's for the greater good. You're right, though--that first picture is worth 1,000 words. Good luck with the drainage challenge.
1 reply · active 571 weeks ago
I can't say for sure that it's for the greater good, but I'd rather err on the side of caution when it comes to curbing the spread of invasive species. (I've done a little volunteer work in one of our local parks and I know they're fighting a Sisiphyean task when it comes to keeping invasives from taking over the wild lands.

Thanks for the good luck wishes. I'll happily take all the luck I can get! ;)
Hi Aaron. Welcome to my world! I'm thinking of investing in an ark in case of emergency. Holleygarden is correct about the Louisiana irises - they love crummy waterlogged clay soil. But if that area dries out in the summer, it could be a problem for them. I adore bog sage and I hear it can take some drought. It's not native but the bees adore it. For shrubs, what about winterberry holly, clethra, itea, and buttonbush (I forget the Latin name)? Callicarpa, Fothergilla, and Rose of Sharon can tolerate some wet (not as much as the others) and work well in my yard too. I think we both deserve a medal for even attempting a garden in these conditions.
1 reply · active 571 weeks ago
That's incredible, Sarah -- I was just researching Bog Sage last night for the first time! I'll have to try it. (Though I'm not sure where I can find it. I'll have to check mail order nurseries most likely.)

I think I killed an itea at one point. I don't think it could take our hot, dry winds. And I believe buttonbush isn't drought tolerant either. Deciduous holly would probably work, but might be too big for this specific space. (And the drainage isn't' quite that bad throughout my property.)

I had Callicarpa for a couple of years but wasn't too impressed with it, so I pulled it out. Sacrilegious?

I do have a Fothergilla in my front border. Absolutely love it. I don't think it could handle the strong afternoon sun in this particular wet spot. And I am trying a couple Rose of Sharons in the back border. This will be the second year for one shrub and the first year for another. So hopefully I'll have some good results this year and will report back.

I do think another good option for this area would probably be Texas Star -- Hibiscus coccineus. It's known as Swamp Hibiscus, so should definitely be able to handle the wetness, but reportedly it's also drought tolerant. Unfortunately it's also hard to find around here, so I might need to go with a mail order supplier.

If they start minting medals for clay soil gardeners, I'll be lining up alongside you!! :)
Look for plants that do well in rain gardens with clay soil since they are designed to handle both drought and deluge. My rain garden stays moistish in the summer. I think the native hibiscus is a winner for you.
1 reply · active 570 weeks ago
Thanks for the suggestion! I do think rain garden plants could be a good option here!

The only issue I have with hibiscus in zone 6/7 is that it's such a late plant to emerge in the spring. At least that's been my experience with Hibiscus moscheutos (Hardy Hibiscus) and I assume Hibiscus coccineus (Texas Star) would be similar...
If you're like numerous landowners, you are possibly a bit cautious of having somebody come in and fit a drainage system in your lawn.
1 reply · active 441 weeks ago
Hi Peter,

I can't imagine the cost of installing a system throughout my lawn to drain water from the heavy clay, but I imagine it would be a very, very large investment.

Moreover, operating on the principle of "right plant, right place," I'd rather find plants like arrowwood viburnum, wax myrtle, rose mallow, swamp sunflower and many others that are perfectly happy in heavy clay that alternates between soggy in winter and rock hard in summer.

Over time, I suspect those plants and their roots will naturally improve the soil drainage.
I totally agree with you Aaron. Its going to cost you a huge amount if you look to install a system to drain water from the heavy clay. But I like the idea if naturally improving soil drainage with help of these plants.

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