Adventures in Iron Continued

In the last post I noted some plants (especially Spinach) were exhibiting signs of iron deficiency. Iron deficiency is characterized by intraveinal chlorosis, which is yellowing of leaves between veins. Manganese deficiency can also result in this type of chlorosis, but in an AP system, iron is the primary culprit.

In investigating this, I found two excellent resources for help in diagnosing nutritional deficiencies in plants. The first is by Wade Berry from UCLA, and the second is by Thomas Wallace at the University of Bristol Agricultural and Horticulture Research Station. Both are excellent in their descriptions and accompanying pictures. I've linked to both of them on the blog roll, except I've named them Nutrient Deficiencies in Plants I and II.

Spinach plants suffering from intraveinal chlorosis (two weeks ago):

Note how the veins remain dark green and the chlorosis affects only leafy material between veins.

As described previously, chelated iron was unavailable, so I experimented by mixing some molasses with a pile (about a tablespoon) of rust that had accumulated under a small pile of nails. There is absolutely no doubt that something in molasses binds iron. This has been documented by others (which is why I tried this). The rusty nails shed most of their rust after soaking in molasses for a few hours, and the rust itself appeared to go into solution. This mixture was then diluted in a liter of water and sprayed on plant leaves and at the base of the plants.

To make a long story short, this treatment did not work... at all - no ifs ands or buts. At least it did not work after a week of treatment. The plants basically looked the same as far as the chlorosis goes, and they were worse off in the sense that some leaves suffered from what I can only call "caked-on" molasses that formed dark, almost black spots on the leaves.

In any case, during the week I was very happy to find chelated iron locally. I also located seaweed extract, which besides containing iron, also contains a host of essential elements and unknown ingredients and which is known to be beneficial to plants. I applied these last week, and these are two of the Spinach plants as of yesterday:

There is no doubt they have "turned the corner". The dark brown/black spots are from the molasses. Some of the poorly damaged leaves fell off or were cut off, but not all of them. Some have recovered and no new leaves had developed chlorosis.

I moved some of the Spinach plants over to my new floating raft system, but left these two behind in the bath-tub grow bed. I somehow forgot to take pictures of the raft-plants this week, but will do so next time. The floating raft system is a post in itself that will be added shortly.

All in all, this has been very educational. I almost feel like I know something about plants! I highly recommend the two sites above on plant nutrition, and that anyone serious about growing their own plants learn basic plant biology and nutritional requirements.

And finally, some people apply molasses in a diluted form to ward off insects. The sweet smell repels many bugs for whatever reason. I used molasses for this reason when I first started my AP system and it did not cause the black spots it caused this time. This is probably just due to the dilution factor - I applied it too thick this time.