Chlorosis in Crape Myrtles

shankins123(7aOKC)August 10, 2012

I purchased 3 Crape Myrtles and planted them about 6-8 weeks ago...into clay soil, but I dug my hole a bit bigger and amended with some composted horse manure and rich garden soil, etc. They're mulched with shredded cypress mulch.

I've watered them just about every day since then because of the extreme heat. They are all approximately 3 feet tall.

Of the three, 2 of them began putting out new growth pretty quickly. Within a month or so, they'd also bloomed. #3 plant has full morning sun, with a little bit of shade in the afternoon. #2 plant has full morning sun with a bit more dappled shade in the afternoon. It's #1 plant I'm a teensy bit concerned about.

This plant has not quite as much full sun in the morning - I'd say it's bright, but dappled. It also had a bit more afternoon shade, so I trimmed back a few branches of the rogue "tree" on my fence line to the west of it and now it's brighter in the afternoon, with some direct dappled sun. It did start putting out new growth at the same time as the others, but I soon noticed that that growth was not as deep crimson as the other two, and that the other older foliage was starting to show signs of veining and outright yellowish coloration. It has not made any attempt to bloom.

So...I got some chelated iron, followed the instructions and watered it in well afterward. That was on Tuesday. My questions are: How soon will I be able to tell if this is making a difference? Is there something else I may be missing?

Thank you!


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Okiedawn OK Zone 7


This is a complicated situation and there are no easy answers.

First of all, the clay itself could be the problem. Plants grown in alkaline clay soils often have trouble taking up the iron that already exists in the soil because of the way clay compacts. Adding more iron doesn't solve that problem.

I know you tried to get around the issue of compacted clay by improving the soil by digging a big hole and working in soil amendments. However, often when a person digs a big hole in clay soil and then improves the soil only within the area of that hole, they have inadvertently created a "bowl" affect where water will sit in the bottom of that area where the improved soil meets the clay and will not soak into the clay. Thus, while your planting area's soil can look dry on top, it can be too wet down lower---wet enough to, in fact, cause iron chlorosis down deeper in the soil where the unamended clay meets the amended clay. Sorry. I hated to even type that, but it is the truth. If the water sits there on top of the unamended clay at the bottom of the bowl you dug when you planted, then one, two or all three of your plants potentially could find their roots clogged with too much water which would interfere with the uptake of the nutrients they need. I hope that is not what is occurring.

I had such dense red clay right in front of and beside our front porch when we moved here that I attempted to do what you did, and all I got was a big clay bowl that held water forever. It was, however, full of well-amended soil---not that the well-amended soil could easily overcome the bowl effect. I had anticipated I would have that sort of problem since I'd already dealt with heavy clay in Texas, so after I improved the soil, I only planted annuals there for the first 5 years, and I continued to add more amendments every year, even double-digging every fall/winter to get the amendments deeper into the ground to help the clay at the bottom of my "bowl" drain better. After 5 years, I felt like the soil had improved not just in the 'bowl' area, but all around it and I could tell it was draining better because annuals no longer were dying after becoming waterlogged during heavy rainfall. Then, I finally planted shrubs and perennials in that bed. They've done well there ever since although sometimes I lose plants there in drought because that area now almost drains too well. (Sometimes it seems like we just can't win.....)

Unfortunately, applying a chelated iron product does not necessarily fix the problem for the reasons I described above. Iron chlorosis is complicated and not very well understood. It is known that it is more common in alkaline soils, compacted clay soils, plants that are over-watered and have too much water clogging the roots and inhibiting uptake of nutrients, and soil that is too high in phosphorus. So, if you have any, some or all of those conditions, the potential exists that you won't see much effect or any effect from using chelated iron at all. Phosphorus alone could be the problem all by itself just by interfering with the plants' ability to take up and use the iron that already exists in the soil.

If all three crape myrtles are the same variety, the one that is having trouble could have been damaged somewhere in its life before you bought it and might have a less vigorous root system. Thus, the issues you're seeing could correct over time as the root system grows and matures. If they are different varieties, the one that is struggling a little just might not have the same degree of vigor as the others. Plants are like people---some have a stronger constitution than others.

I don't necessarily think the amount of sunlight is a big problem. I've had crape myrtles bloom perfectly fine in dappled shade and in only half a day of sun.

If you haven't had a soil test, that's where I would start. Many soils hold excess phosphorus and if that is the case with yours, then you need to be sure you do not add any more extra phosphorus by using a fertilizer with phosphorus in it.

Also, deficiencies of some micronutrients like manganese can give you symptoms that mimic iron chlorosis. With a soil test, at least you'll know if the soil has the right balance of nutrients.

Other than getting a soil test, I'd watch the watering carefully because of the potential for water to pond where your amended soil meets the unamended clay. It may not even be a problem at all, depending on how well your clay drains. I have the kind of dense, tightly compacted clay that does not drain well at all. Your clay, while dense, may have more silt or sand in it than mine did or may not be as compacted and may drain better, so you might not have that bowl effect.

For the record, the current recommendations for planting trees and shrubs in beds in dense clay is that you not put amended soil in the hole if you are planting at grade level, precisely because of problems caused by the bowl effect. You can get around this simply by mounding up the soil above the planting area a few inches and planting into a raised bed. Just planting a few inches above grade level helps avoid waterlogging of roots when you're dealing with dense clay.

I think in the long-term your plants will be fine, but if the clay beneath the soil drains slowly, you'll have to be careful that you don't overwater that area. If a soil test shows your soil is too high in phosphorus, that just has to correct itself over time. You really cannot remove the phosphorus from the ground, but you can help by using a fertilizer with a low amount of phosphorus, or using one with no phosphorus at all. In the last 10 or 15 years, soil scientists and horticulturalists have developed a better understanding of how many soils in this part of the country have excess phosphorus, so it is pretty easy to find fertilizers formulated for this area that are all-nitrogen, or formulated with very low phosphorus.

I don't know if anything I said helped. Even if you didn't have clay soil or any of the other issues, chelated iron results can vary a lot in how quickly they show results, so you just have to watch and see. I tried chelated iron with my banana shrub two years in a row and never saw one positive result whatsoever so I quit using it.


    Bookmark   August 11, 2012 at 10:44AM
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Wow - ok; thanks. I guess I will just have to wait and see. While I did amend a bit in the hole, it wasn't extensive by any means. They are all the same variety (at least tagged that way - won't really know until this one blooms). I'll get a soil test to see what I'm dealing with. Oddly enough, this one seems to really take up the water more than the others - it drains down more quickly. I'll kind of hold back a bit on the water; I just didn't want to underwater in what was crazy heat for a couple of weeks.


    Bookmark   August 11, 2012 at 5:19PM
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Okiedawn OK Zone 7

Sharon, I understand completely. I was thinking how brave you were to plant in this kind of summer! Maybe that area under that plant is draining too quickly. Who knows? On our property, the soil varies slightly every few feet which makes it hard to figure out why one plant will looking unhappy while the plants on either side seem fine. I spend a lot of time shrugging my shoulders and saying "wonder what that's about". lol

If you didn't amend real heavily, then the bowl effect should be minor if it is an issue at all. I always plant crape myrtles in unamended clay because they seem to tolerate it just fine and I cannot afford to create a bowl effect here on our slow-draining clay.

We planted very small bare-root fruit trees back in the winter when it was raining pretty regularly and it is a struggle this summer to keep them happy. I wouldn't have planted them at all if I'd known the kind of summer we'd have. Hindsight is always 20-20.


    Bookmark   August 12, 2012 at 6:15PM
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Well...I'm just going to have to baby them along and see what happens. One of the other two is now showing slight signs of the same thing, so maybe it's a combination of heat, transplant shock, etc., etc...not to mention the terror of someone checking on them daily!!

One other question...I now own 5 2ft-high spirea bushes. I have them in morning sun/afternoon shade (still in their pots), waiting for summer to wane FOR REAL before I transplant them. Should I be ok just transplanting them into the clay? It's about 5 ft. behind the crape myrtles I've referenced above.

I got both of these thinking that they were pretty forgiving and tolerant of most soils/light conditions that I have I'm only slightly paranoid!

[ I did plant the crape myrtles before the extreme heat hit us - I may be off on how long ago that was, but I knew that I had a better chance of keeping them happy in the ground than I did in their pots, or so I thought!]


    Bookmark   August 13, 2012 at 2:16PM
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Okiedawn OK Zone 7


With the spirea, if you can keep them in the pots and keep them happy another 2 or 3 weeks, that is what I would do. You want to get them in the ground as soon as possible for fall (which is the ideal planting time for them) so they can establish their root systems before really cold weather arrives, but it would be crazy to put them in the ground now. If you are in the part of OK that is getting a cool-down and rain this week, it wouldn't be as crazy to plant them now as it would be in my part of OK where the cool-down is pretty weak. I think if you put them in the ground before mid-September, they'll be fine and can adjust to being transplanted before the frosts and freezes hit.

Spirea is pretty tough once established, but you'll have to keep a close eye on them the first couple of years until the roots are well-established. They may show chlorosis if your soil's pH is 7.0 or higher. They are happiest in soils that are a tiny bit acidic but they tolerate neutral soil. If I was going to plant them (but keep in mind my unimproved soil tests at about 8.2 pH, as does our water), I'd buy a big bale of peat moss and work it into the top few inches of soil. I'd do this more because of its acidity than for its ability to break up compacted clay. Then, when I fertilized I'd use the kind of fertilizer used for hollies and azaleas--something like Espoma Holly-Tone or the Miracle Grow for Acid-loving plants. If your soil tests acidic to neutral, you wouldn't have to use the peat moss or add a fertilizer for acid-loving plants.

This summer and last summer are beyond awful in terms of keeping plants well-watered and protected from the sun and heat. It is a wonder that anyone has anything left alive at all. This whole state is just a tinderbox. I keep telling myself that "surely next year will be better", which is exactly what I kept saying all of last summer too.


    Bookmark   August 13, 2012 at 7:26PM
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Yes...that's what I thought, too, as far as waiting a bit to plant. I'd kind of decided to wait until next spring for this shrub line, but...there they were at 50% off at Horn's and I just couldn't say no (!) They are happy to be where they are for the moment and that will give me a bit of time to get things ready to plant them. Thank you for your suggestions in that direction.

Can we claim "third year's a charm" or something so that next year isn't as scorched as these last two have been?
I think we're ready for something really nice, really temperate. :~)


    Bookmark   August 14, 2012 at 11:24AM
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Okiedawn OK Zone 7

I'm hoping for another 2007 or 2004 in 2013, minus the flooding. To be honest, I wouldn't mind a little flooding (obviously we don't want so much flooding that homes are flooded, etc.) because it would help refill ponds, lakes and creeks.

If El Nino fails to materialize, or takes the heavy rainfall somewhere else and we have another drought like this one, that will be just unbelievable.

    Bookmark   August 14, 2012 at 1:07PM
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