Cracked!

Mind the gap!

Just a pic to illustrate the challenge of gardening on compacted Tennessee clay 'soil' (subsoil?)

It looks from this image like we hadn't had any rain in months.

But this is just what my soil looks like if we go a couple weeks with warm weather and not much rain.

(This pic was taken about a couple weeks ago. At the moment, much of the back yard looks like a shallow pond since we've had several days of hard rain with flood warnings across the area. But next time we have a couple weeks of dry weather, it will go right back to this cracked look.)

Could I amend the heck out of it? Sure, but it would be back-breaking, soul-crushing, expensive, time-consuming and ecologically-questionable.

Instead, I try to find ultra-tough plants - many of them natives - capable of surviving and even thriving in this pottery material.

Ultimately, where the plants thrive, I find that the soil does improve over time. Slowly. In a few hundred years of letting Nature work its magic, I might have some nice loam! 😉

Daikon as Clay Soil Amendment (and Tasty Vegetable)!

Daikon foliage, pre-deer (the stems coming out of the daikon at the bottom of the photo are actually from another annual - redwhisker clammyweed - that was growing in the same area where I scattered the daikon seeds)

In the U.S., when we think of radishes, many of us think of the cute little red skinned radishes.

I like those little reds as much as the next guy, but let me tell you something - they do not thrive on heavy clay. And by 'do not thrive', I mean that when I tried growing them, most of them failed to develop anything resembling the round, bulbous shape that the word 'radish' conjures. It was an abject disappointment.

But daikon radishes - sometimes known as tillage radish - is in a different category altogether. In fact, daikon radishes are so renowned for their ability to penetrate compacted clay soils that some people use them as a winter cover crop to aerate the soil (example Delta Farm Press). Note that if you're growing it to amend the soil, the idea is not to harvest the radish, but to allow it to winter kill and then decay in the soil.

Daikon foliage, post-deer (or possibly post-rabbit)

Having just removed some shrubs from a garden bed, I had some bare soil in September and no firm idea what I wanted to plant there yet. I thought I'd do a trial planting of daikon to see (a) if it could make a good cover crop and (b) if I could get any sizeable radishes from the bed for eating.

I happen to enjoy eating daikon radish, for instance sliced and added on top of a salad.

I sowed the seeds (from Sow True Seeds) in September, gave them a couple drinks of water to get started and then basically left them alone to fend for themselves during two months of severe drought that followed.

How did they fare?

Color me impressed. As a cover crop, daikon produced a nice head of leaves that sheltered the soil and blocked weeds. (The leaves are also edible, fyi.)

And the roots actually did manage to penetrate the hard-as-concrete parched clay soil. In fact, the soil was so tight that I had to water the plants just to pull some of the radishes without having them break in the middle.

A couple of daikon radishes pulled from the concrete, er... clay, soil

Now, it's true that my radishes did not reach the mammoth portions of ones grown in sandy-loamy soils. In Japan, where daikon radishes are quite popular, the roots can easily be 12 inches long with the diameter of a baseball bat. My daikons were only about one-third that size, but consider their growing environment and the lack of rain (which would probably have softened the soil and allowed the daikon root to expand deeper and wider), I was quite impressed and pleased with their performance.

How was the taste? I was expecting that the lack of rain would have made the radishes hot and spicy, and indeed the first daikon I ate was almost too hot to handle, but the subsequent ones I consumed generally had just enough bite.

Sliced daikon makes a lovely salad topping

I did run into two problems - deer and rabbits.

The daikon leaves seemed mainly untouched in late October, but throughout November, I saw more and more herbivore damage (and telltale deer droppings scattered around the backyard pointed to the culprits). I figured the deer shouldered all the blame, but late in November, I spotted a well-fed bunny scampering from the radish patch, so I'm dividing the blame among both types of critters.

Still, I can't blame them too much. A nearby wood has been mostly clear-cut this summer, and the drought meant that much surviving wild vegetation was parched, dead or dormant. Finding this green salad bar in my backyard probably seemed like quite a treat - maybe even a life-saving one - for the critters.

I saved some seed and hope to try again in the spring. If we have normal rainfall this winter (the last week has been promising), hopefully there will be plenty of other wild greens for the local herbivores to eat and I'll get a chance to see how the daikon fare without being denuded of their foliage. (Neither the rabbits nor the deer touched the radish root, so technically I could still dig up and eat some of the daikons, but I think I'll let them decompose over the winter to help the soil.)

Overall, I'd say this experiment was quite fun, tasty and successful. So much so, that I plan to grow a lot more daikon in the future. And for any other gardeners out there stuck with heavy compacted clay - consider giving daikon radishes a try!

Evidence of Poor Drainage

A photo is worth 1000 words:

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.

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!