Chlorosis is more complicated than just the iron content of the soil. There may be plenty of iron in there, but conditions are such that the plant cannot access it. Soil temperature, pH, and moisture vs. oxygen content can all be factors.

Iron leaching from the rebar (i.e. rust) will be in a form chemically unavailable to the rose. If you want to test the effectiveness of the rebar, you'll have to use it without adding the iron sulfate. You'll be disappointed with the results.

:-)

~Christopher

As Christopjer says, putting metallic iron in the soil will have no effect. There is already lots of iron in the soil that is not available to the plant. If you lower the pH to 5.5-6.5, it will become available. Sulfur, 1/2 cup under the mulch, repeat in six months, look for improvement after a year. Also you can add available iron. This is "chelated" iron, or you can mix iron sulfate granules with compost.

Iron from rebars will do the same thing if you sprinkle iron filiings on the soil: not much.

Iron deposits do not migrate well in soil. It binds with the soil molecules and doesn't move much over time. Remember the times you unearthed a rusted nail or piece of iron/steel metal in the soil that had lain there for years? We've all had that experience. The soil immediately around the metal had some rust coloring, but no evidence of that more than an inch from the metal.

If there is an iron deficiency, use a liquid form, iron chelate, to augment the soil. It has properties that allow it to migrate freely.

Bart, I agree with all previous posters. Additionally you have committed the scientific fallacy of changing two factors at a time during testing :). Ferrous (iron) sulphate applied in the soil will fight chlorosis to some extent, strangely enough not so much due to its iron content but due to the acidifying effect it has on soils. But one needs a relatively large quantity. For soil applications you can use an iron chelate suitable for your pH. Foliar applications of iron sulphate are very effective, more so than foliar applications of iron chelates.
Nik

My grandmother put nails in the ground, under her hydrangeas to raise the acidity -- but I never saw that it did much.

A handful of soil sulphur, however, is pretty effective. In my highly alkaline environment, it is the ONLY thing that has been effective.

Sometimes placebos can have remarkably good results. It can't hurt.

Hey Bart
In my area, fighting chlorosis is an ongoing problem, as both soil & water are very alkaline, tending to make iron & some other nutrients unavailable to plants.

One very helpful thing I've tried over the past year is planting in a mix that is 1/3-1/2 pine fines (finely shredded pine bark). It helps the soil texture & is acidic as it breaks down. I buy a "landscaping mix" that is mostly very finely ground pine bark, but have also used pine bark mulch. I've also started using some gypsum (calcium SULFATE). Although promoted as improving soil texture, it also provides a form of available calcium & sulfur to the soil. (have read arguments pro & con re. this)

So far, it seems to make a more lasting effect than periodic treatments of iron sulfate, etc. Most of the literature regarding local gardening advises correction of soil alkalinity, to make nutrients available, rather than simply supplying more iron. We constantly add lots of oak leaves, shredded pine & anything else to try to lower alkalinity.

Don't know your local geology, but this area is ancient seabed with exposed soft limestone, little soil, & large deposits of caliche, a cement-like calcium carbonate formed from the percolation of rainwater through the limestone.

Ironically, plants often lack adequate calcium, because the carbonate form isn't available to them.

A good example re. iron availability: when I took an animal nutrition course, was surprised to learn that iron oxide isn't available to cattle. Yet it is added to most cattle salt licks because people associate "iron" with "red colored", so red colored salt licks are what most folks buy for their cows. But in the ingredient list, even the red licks contain iron SULFATE, the form actually available to cattle.

This post was edited by bluegirl on Thu, May 29, 14 at 12:42

Last year my new baby hydrangeas suffered from chlorosis. My soil is acidic, and I'm pretty sure the chlorosis was caused by soil compaction (sticky clay, anyone?). Mixing fine mulch and fallen leaves into the soil for my new(er) hydrangeas seems to have fixed that for me. I will have to dig the older ones up in spring and do the same.

Yeah, but just as a fun, easy experiment,nobody wants to try it? guess not...
Like I said, it seems to be helpful for me...bart

Well who knows? maybe it IS helpful. I can think of any number of *proven* facts that were altered or even reversed years later.

And I've even done the same thing--dumped boxes of rusted brads in pots. Didn't seem to hurt anything. Maybe iron sulfates form from them, too, or maybe iron oxide IS adsorbable, to some degree.

If it seems to help, ignore the *facts*--results matter. Maybe I'll stick some rebar in my pots, too :D

Putting nails in the soil is liable to cause injury to someone in the future, and it is entirely futile. Respectfully--please don't do this or recommend it.

Rust is ferric oxide, which is insoluble and unavailable to plants. Many soils have a great deal of this material, but some plants, including certain roses, will be unable to get enough iron if the pH is 7 or higher. But they can get enough iron from acid soils even if the amount of iron in the soil is much lower.

Agreed with Michael -- metallic iron and iron oxide (rust) have been tried for generations, and they simply don't work. Iron nutrition in plants is well-understood. It can be a challenge, but it is manageable, either through lowering soil pH (the best solution in most cases) or with the use of chelated forms. Sprint 330 is a good material for soils up into the low- to mid-7s; Sprint 138 will work up into the low 8s (as soil applications), if you simply cannot bring the pH down.

Has anyone tried foliar application of iron sulfate? The recommendation for plants-in-general is 4-5 TSP (a slightly rounded TBS) per gallon plus a squirt of soap. There may be a risk of burning foliage.

This post was edited by michaelg on Thu, May 29, 14 at 11:10

Bart, if it helps, decades ago my dad tested this theory. I have dug up probably a ton of rusty metal of every random thing one might imagine. I joked that I dug up the kitchen sink, bathroom sink, faucets, pipes and the wrench all in the front yard, but truthfully I did find all of those there. We still have a problem with lack of iron.

I heard later that it would take 100 years to actually convert to something a plant can use and I don't think that speaker was even thinking of our alkaline soil that would make it even harder to become available.

Okay! okay! Agree not to stick nails & rebar in the ground to impale unsuspecting diggers. I just added a fistful of almost completely rusted out fine brads to a couple of potted roses, many years back.

I suppose this is as (un)useful as the old recommendation to nail a few galvanized nails into pecan trees to supply zinc. (haven't looked that one up lately, probably useless & harmful)

I've fatally burned up a couple of roses using iron sulfate applied to the ground, even at the recommended amount & with plenty of watering, so I'd use it with caution & not during the hottest part of the year. Haven't dared try foliar application here, but used to use it often in tropical zone 9. Azaleas & roses would green up significantly within a couple of weeks. But for long term improvement, we used sulfur annually & constantly added oak leaves & pine bark.

So this year I'm working on the big picture--moderating soil alkalinity--instead of trying a quick fix. Requires a lot of patience in a deserty climate, as things break down very slowly. But! it's live oak leaf dropping season here--we scored 50+ bags & mulched the heck out of everything--and got 3 inches of rain afterwards!

This post was edited by bluegirl on Thu, May 29, 14 at 12:50

michaelg,
I foliarly apply iron sulphate to citrus regularly. It's more effective than iron chelates applied foliarly and much cheaper too. I have not had the need to do it on roses so I can't comment on any tissue toxic effects. As with any foliar spray, it woud be wise if spraying is performed during the cool periods of the day, not under full sun and not during excessive heat. Also plants should not be under water stress. Being cautious I would never use iron sulphate in tandem with horticultural oils or apply both of these during the same period of 3-4 weeks. I suppose soap in your recipe is meant to act as a surfactant adjuvant.
Nik

PS. Indeed, the iron absorbtion mechanism is quite well understood. People have been sticking pieces of iron in the ground forever but the fact that it does not do any good has been known by scientists for more than a century. I have a University of California reprint of a short diatribe on citrus fertilisation, by a certain Joseph Hillman first published in 1907. Therein, iron sulphate (mentioned as sulphate of iron) is recommended for citrus chlorosis. As an interesting side note, the publishers of this booklet were an institution called 'The Nitrate Propaganda', obviously an agency of the late 19th centure Chilean-British mining cartel. In the same booklet we learn that in 1907 in the US, 100 pounds of Sodium Nitrate (called Nitrate of Soda) cost between $2 and $3.

This post was edited by nikthegreek on Sat, May 31, 14 at 2:09

See, the thing with adding stuff like iron filings, etc., is that they need free acidity (soil pH below 7) to dissolve. But if you have a soil pH low enough, you won't have iron chlorosis in most cases, and hence no need to add iron filings.

Thanks, bluegirl :)

And thanks, nik. I wonder if the iron chelate molecule being so big makes it hard for it to pass into the leaf (#notachemist). I tried spraying it once on a rose and it didn't seem to do anything.

michaelg, Iron chelates do have an effect when applied foliarly (at least on citrus). I'm not an expert either thus I cannot comment on the reason they are not as effective as iron sulphate applied foliarly.. It is just that you need a higher concentration of iron and more applications than iron sulphate. Also spraying should be done at dusk.The difference in price being what it is, it seems quite silly to apply chelates foliarly. Having said that many commercial foliar ferilisers (mainly targeting amateur growers) do contain iron chelates. One thing to note is that if one does decide to use iron chelates foliarly, the cheaper ones (e.g EDTA) will do fine, no need to go for the more expensive ones like EDDHA which are to be used for soil drenching when pH is quite high.

One thing to note regarding iron chlorosis is that phosphorus competes with iron (one more reason iron chlorosis is common in calcareous soils which are commonly rich in phosphorus). Often unnecessary phosphorus fertilisation can make iron deficiencies worse. In the same vein, it is better if iron is administered some time before or after phosphorus fertilisation.
Nik

Excessive phosphate also causes zinc deficiency. It's really a shame that so many gardeners have been led to believe that you need extra phosphate to grow roots, flowers, and fruits. Once the stuff is in the soil, you can't get rid of it. The high-P "bloom buster" fertilizers are really a form of pollution.

Yes, ammonium sulphate can help in, temporarily, acidifying the soil (so can its potassium equivalent potassium sulphate). Care must be taken since excessive application may cause a sudden excessive lowering of the pH causing root burn and shock (leaf drop etc). I use ammonium sulphate as a nitrogen source in my calcareous soil. One thing to note is that the nitrogen in it is not readily absorbable in its enirety by most plants and needs to undergo the microbial nitrification process. This is slowed down if temps are low. Also, when applied in calcareous soils it either needs to be covered up with soil or light irrigation should follow application. N percentage is 21 and S is 24% i.e. fertiliser formula is 21-0-0-(24S). I would hesitate to use ammonium sulphate if sulphur is also being applied as a soil ammendment without checking with an expert first.
Nik

This post was edited by nikthegreek on Thu, May 29, 14 at 16:13

michaelg,
Indeed this is often the case with regards to phosphorus overuse. I should note though that cultivating roses, especially if pruning is commonly exercised along with deadheading and removal of debris from the soil, is often not too dissimilar to cultivating a productive crop. In such a case phosphorus, along with the other nutrients, is removed from the garden's ecosystem and might, in some cases, need to be replenished in some way.
Nik

PS Which reminds me of the fact that one can grow a plant in a sealed glass container for decades once one has initially provided a dose of water and nutrients, as long as energy and heat is provided in the form of light. It is easier said than done since the plant's growth pattern should fit the container and disease or pests should not be allowed to exist in this isolated ecosystem. It has been demonstrated though.

This post was edited by nikthegreek on Thu, May 29, 14 at 16:42

What could be dangerous about growing a rose up a rebar teepee?????

I have a few rebar teepees in my garden. The roses near it are no healthier than the ones at a distance. This garden is entering its 5th year. The rebar has been in use here for 3-4 years.. I use them because I found a stack of them on the property. I also like the rustic look.

I have made some trial applications of foliar iron sulfate to see if it burns roses. I'll let you know next week.

Bart, my impression is that no one is worried about rebar teepees (I agree, they look great) but about mixing nails or pounding short stakes level into the ground where an unknowing person could get injured by them later.

We use soil applications of iron sulfate when needed, but it is very easy to burn leaves with it, so if you do that, do it carefully!

I suspect that on leaves, chelated iron is not absorbed at all, since as someone said above, that's just too big a molecule. Chelates are dynamic though -- the free Fe2+ ions can pop out of them and back in. While out and exposed, they could be absorbed foliarly. In soil, a chelate is working by preventing the iron from attaching to cation exchange sites on the soil. As water is swept into the roots, the full-size chelated molecule gets sucked into the root, not into living cells, but between them into the intercellular spaces. Then, as mentioned earlier, they dynamically release and recapture Fe ions. While such an ion is free and unprotected, it also becomes fair game for one of the root's protein-based ion pumps on a cell surface, and get quickly pulled across into the cell, leaving the chelator coating behind.

Dr. Manners, thanks very much for the scientific explanation of something that many may know out of experience but did not know why.

PS This all is quite tricky and one sometimes finds slightly contradictory references in the public domain. Below is a link to an older puplication which refers to trials on a particular kind of citrus (Encore,which is a mandarin hybrid) , mentioning that foliar application of iron chelates had the same effect using less iron than foliar application of iron sulphate, although I still suspect iron sulphate would be much cheaper. What really surprised me was the third method used, that of applying sulphuric acid foliarly. I wonder what would be the mechanism of such action.
Nik

Here is a link that might be useful: The recovery of citrus from iron chlorosis using different foliar applications. Effects on fruit quality

This post was edited by nikthegreek on Sat, May 31, 14 at 1:20

Well citrus iron nutrition is weird. When I was doing my doctoral research at the Homestead experiment station, we observed that lime trees, apparently regardless of rootstock, would show strong iron deficiency on the new growth flush (soil pH a bit above 8 usually, on almost pure calcium carbonate "soil"), but as soon as another, newer flush would begin, the existing leaves would turn dark green! So those trees were getting iron from somewhere, just not enough to supply the newest flush. Roses, on the other hand, can show chlorosis on all of the leaves at once.

Malcolm Manners, it's always interesting and helpful to hear from you. Would you explain why you chose soil-applied iron sulfate as the tool of choice and how you use it?

Michael, When we see iron chlorosis here, it is most often near a concrete-based building and so is due to high soil pH. And here on the central Florida ridge (ancient beach sands), our soils have very low buffering capacity, so lowering the pH tends to be fairly easy. So FeSO4 is a good way to quickly bring the pH down (hours, vs. months for S) while also providing some iron. Of course you have to be careful with it near sidewalks or buildings -- if not rinsed off the surfaces, it will quickly oxidize to rust, leaving nasty stains. But you can green up a chlorotic plant in a week or two.

A week ago, I applied iron sulfate to foliage of three roses (and a chlorotic bonsai fig) to check for damage to the leaves. There was no burning. A couple of young leaves on 'Aloha' seem unnaturally wrinkled, but I'm not sure that is damage

One TSP/ quart with a drop of soap, applied to well-hydrated plants in the A.M. The high temperature since then was around 85. It might burn in hotter weather.

Many western soils are somewhat alkaline. My own garden has a pH up around 8 to 8.5. The soil sits on a limestone bedrock. It is very good for the growing of grapes, and yes, there are several excellent wineries within a couple miles of my house. We probably should have a hobby vineyard, but that would really be a lot of work. Instead I have planted mostly native trees and shrubs outside the fence and my roses within it.

And yes, I have had chlorosis problems with some roses, mostly HPs and rugosas. The most severely affected I gave up on. There are so many that are happy here that I decided not to baby the unhappy ones. Well, I do make some exceptions. However recently I have noticed that many of my peonies, both tree and herbaceous, become very chlorotic immediately after blooming. For some it starts while blooming is taking place, obviously a time of higher nutritional need. I do not allow them to produce seeds. Just the other day I gave them all a good foliar spray and watering with chelated iron. I am hopeful that this will restore them to better health. Note: good old Festiva Maxima is the most resistant to this effect. Now that is one tough peony, and gorgeous as well!

Folly