Category: Friday puzzle

Friday’s puzzle was tricky!  I will preface the answer by saying I don’t do a lot of container plants except for annuals.  When I plant up annuals into soilless potting mix (which is dehydrated), I work in the water thoroughly into this fluffy medium.  Friday’s situation was a little different.  The Clematis are more or less permanent residents in these planters, so I use real soil rather than potting mix.  (This will reduce or eliminate the shrinkage you’ll get if you use soilless media, as these highly organic materials steadily decompose.)

But what I thoughtlessly did was to mix water into my nice screened clay loam like it was a potting mix.  The result of vigorous mixing is to break down the soil structure and drive water into all of the pore spaces, resulting in a totally waterlogged soil:

After my "D’oh" moment when I realized my error, I potted the second Clematis into loose soil and let gravity work the water into the larger pore spaces. This passive approach protected the soil structure and left some of the pore spaces filled with air rather than water, so that the water drained through rather than sitting on top of the compacted soil:

This demonstrates one of the rules of working with landscape soils:  you should avoid any potential compaction when the soil is wet.  (It’s the same reason you shouldn’t stomp on wet backfill as you’re transplanting trees and shrubs.)  As Ginny pointed out, you’ll create a cement-like structure – not conducive for water movement, oxygen availability, or root growth.

A few weeks ago I showed you photos of iron toxicity in a Clematis planted in a soggy soil (perched water table).  Because this area is just not conducive to plants, we’re putting in a small deck.  This necessitated the excavation of two Clematis, which were both suffering from wet feet.  (Needless to say the root mass was very small and shallow on both plants.)  We decided to put them into large planters with conical trellises and use them as deck plants.

During our pond excavation we retained the topsoil and sieved it for uses just like this (for woody planting, not annuals).  The soil is a clay loam and has been stored in a garbage can to keep it dry.  Anyway, the first pot I filled with this good soil, added water, and worked the soil with my hands to ensure it was thoroughly hydrated.  As holes developed, I added more soil and continued to work it in by hand.  I then installed the first plant and watered it thoroughly.

After observing what happened during the next several hours with this plant, I installed the second plant differently – I watered the soil but did not work it by hand to hydrate it.  I added the plant as before and then watered everything thoroughly; I added soil where holes developed.  I then redid the first container in the same manner as the first.

What happened to the first container that caused me to change my installation technique?  And why didn’t it happen with the second container?  Answers and photos Monday!

Well, Dr. Rohwer was right – he thought you’d get this more easily than I did!  Ray and Jon were spot on – this is classic juglone toxicity from those walnut trees (Juglans spp.) you see in the background.  Many of these leaves ended up on the roof, leaching into the rain barrels (good sleuthing Ray and KennyG!), the water in which was used in irrigating the vegetable garden.  In fact, Dr. Rohwer divulged that the rain barrel water was quite brown from the walnut leaves.  Thus, the tomatoes met an unhappy end, because tomatoes definitely do not love walnuts.

Juglone toxicity, an example of allelopathy, is an interesting phenomenon – it does not affect all plants equally.  In fact, this clue was given in the puzzle, when Dr. Rohwer mentioned the "garlic and carrots, amongst young beets, onions, kohlrabi, and bolting radishes and spinach" also in the garden.  Many of these vegetables are known to tolerate juglone, as are various landscape plants.  (There is an excellent publication from Purdue on juglone toxicity with lists of tolerant and sensitive species.)

Juglone is most prevalent in the nuts, roots and leaves of walnut trees.  This makes sense:  germinating walnut seeds and expanding root systems are both able to kill their competitors, retaining more resources for themselves.

Juglone tends to be less of a problem for established trees and shrubs, as their root systems are more extensive; seedlings would be the most sensitive stage.  And walnut wood used as part of a wood chip mulch has not, as far as I know, been shown to cause juglone toxicity in landscape plants. 

We’re glad to have Dr. Rohwer back for another visit!  Here’s his Friday quiz – see if you can figure out what happened to his tomatoes.

"Exhibit A is a tomato in our garden. We had 2 tomatoes last year a couple feet away from this one, they met the same fate. Wilting at about flowering time, and water did not resolve the wilting. Previous to last year, the area was turfgrass for who knows how long. There was no vascular discoloration or oozing."

Charlie also included more evidence: "Exhibit B – arrow points to former location of the wilted tomato behind the garlic and carrots, amongst young beets, onions, kohlrabi, and bolting radishes and spinach. Exhibit C – arrow shows the former location of the tomato.  In the far background you can see our roof. We have 2 rain barrels collecting most roof runoff." This water is used in their vegetable garden.

 
And here’s a bit of diagnostic information: "Plants sensitive to this condition exhibit symptoms such as chlorosis (foliar yellowing), wilting, and eventual death."

Can you figure out what happened? Answer on Monday!

Friday’s quiz was a tough one. Bernadette and Lisa B. gave it a good shot, guessing that this might be a phosphorus deficiency. While they’re on the right track (it is a nutritional disorder), the mineral of interest is iron, and it’s a toxicity problem, not a deficiency.

Under wet conditions (the affected Clematis is in the part of our landscape with a perched water table – see the March 15 posting), iron is predominantly in the Fe⁺² form (ferrous) rather than the Fe⁺³ form (ferric). The ferrous form is easily taken up by roots, and when leaves accumulate too much iron they turn reddish-brown.  This diagnostic characteristic is called bronzing, and it’s different than the reddening caused by anthocyanin accumulation.  (As an aside, nonagricultural landscapes rarely have phosphorus deficiencies and are more likely to contain excessive levels of phosphorus.)

Finally, all this talk of iron has reminded me of one of my favorite chemistry puzzles – see if you can figure out what this is:

Give up?  It’s a ferrous wheel!

These two Clematis are the same cultivar growing in my landscape about 15 feet apart. Both are growing on a fence facing north. Compare the leaves of the two:

Normal, happy Clematis

Not-so-happy or -normal Clematis

What do you think is causing the leaf discoloration? Very large hint: this is not a biotic stressor. Another hint: you’ve seen this part of our landscape before…back in March. For full credit, identify both direct and indirect environmental stress (in other words, [1] what is directly causing the discoloration in the leaves, and what is allowing [1] to occur, thereby causing stress indirectly)?

Answers on Monday – have a happy 4th of July.!