Here is a plant growing study I stumbled across tonight, and found very interesting. As some of you know, I have a little nursery where I grow, among other things, citrus. I do add micronutrients to my media, and sometimes compost. The media consists mostly of pine bark. I have never done a good comparsion on the effect on growth, using the various mixes, but I have always believed the additives help, though I have noticed that many plants, planted in plain old pine bark, do just fine. This evaluation, by Ohio State University, makes me question my assumptions about the necessity of adding micros. I realize the study is a little old, but I see no reason it would not still be valid. Comments are appreciated.

Ned

http://ohioline.osu.edu/sc165/sc165_4.html

I don't know much about the specific compost that they mentioned, but it seems to be the source of the micronutrients, not the pine bark. Since I just add potting soil with my pine bark, I think I will continue to add trace elements.

Thanks for responding Skeet. Even though some materials (gypsum, dolomitic lime, and granular sulfur), were added to the basic mix, I don't think they used compost in the control mix.

I may experiment using those additives, but I don't plan to make any drastic changes until I am convinced this works.

There is one thing to be said for this formula, it is easier for the average person to come by, and is cheaper.

Ned

Ned, a couple thoughts. First 18-6-12 slow release fertilizer would not be the fertilizer formula that I would use for growing on any plant. However, it is an excellent fertilizer formulation for rooting cuttings and germinating seedlings. But that aside, I would make a couple comments. First, I do not know what amount of fertilization that is required by Rhododendrons. Second, normally commercial growers do not use hard wood bark as an ingredient in growth mediums, because of the danger of a manganese toxicity. I did notice that in the Ohio State experiment hard wood bark was added at a low rate (3:1:1). Also, they do not mention the amount of calcium supplied by the irrigation water. Normally if the irrigation water contains at lest 40 ppm Ca, no additional calcium additive is added. The University of Oklahoma has reported that an over supply of calcium retards plant development (this research was done on tree seedlings). In Ohio State's experiments they added both calcium and dolomite. But again it was in all trials including the control. As reported, EVERY PLANT REQUIRES micro nutrients. Evidently, for rhododendrons enough trace minerals must have been supplied by the growth medium (hard and soft wood bark). Research by Dr. Carl Whitcomb, PhD. (whose name is listed in the link you posted) a professor at the University of Oklahoma and earlier a professor at the U. of Florida shows a large benefit in both plant quality and growth by the addition of NPK and micro nutrients (especially Micromax). All of Dr. Whitcomb's years of research was geared towards the propagation and on growing of trees. The results of Dr. Whitcomb years of research can be read in the 1,129 page book "Plant Production In Containers II". I will add that Ohio State is a real leader when it comes to research, particularly on bedding plants and greenhouse crops. I'm sure their trials were conducted fairly, and properly. As for the use of NPK plus micro nutrients I will certainly continue to use them in all of my growth mediums and fertilizing schedules, most especially on citrus trees. Thanks for the link. I enjoyed it. It was nice of you to post it.

Thanks for your comments and insight Millet. I don't intend to change my use of Micromax in my citrus because of this report, but I did find it interesting, especially since I do grow some plants without micronutrients. I have grown these plants with, and without added nutrients, and they seem to grow just as well either way. When reading the report, it did occur to me that rhododendrons might be better able to absorb micronutrients from highly organic mixes.

Ned

Nedd,
usually citrus trees havev abbility to conserve some micronutrients (finding of Dr. Castle, UFL), so can be grown in very infertile sandy soils of Florida (see publications of Dr. Wutscher, USDA) without micronutrient treatment so the soil.
Micronutrient deficiences were solved by micronutrients sprays to the foliage, as also reported from Australia, were Poncirus trifoliata ist grown in high alkaline soils, and the occuring zinc and iron deficiency symptomes are cared with micronutrient chlelate sprays to the foliage, as soon as the become visible.

So, I grown my Citrus in Seramis a complete sterile clay granulatum. So I need a full solution fertilizer, to handle the micronutrient demands of my plants properly.

Because of the infertile media I need the micronutrients in the fertilizer, but if you have organic fertilizers, I guess simply adding some good compost, and no micronutrients fertilizer will be neccessary, as the need of the plants is very low.

I came upon a sentence while reading about the fertilizing of citrus trees planted in ground, and I have posted it below. Upon reading it, I immediately remembered this post concerning micronutrients. Here is what the author of the book "Growing Citrus In Florida" said:

"A good deal of research, however, suggests that micronutrients are usually not needed until leaf-deficiency symptoms arise."

However, three pages later the same author writes, " It is better never to let deficiency symptoms appear than to correct them after they have retarded growth."


My guess is that the best method of insuring that a micronutrient deficiency never happens is to apply micronutrients before any deficiency symptoms show up. I'll leave it up to the readers of this thread to make their own interpretation. - Millet

Millet,
I agree: Difficult.

It has to be considered, that micronutirients, as the name remembers us, is needed only in very low quantities.
Especially Boron: If less, we encounter problems, but only a slight excess, and we encounter damage... To here, the borderline betwen excess and less is very narrow and very difficult to maintain.

In free ground, micro-nutrients are often controlled by soil analysis, but in pot... well, I thinks that's to much. Usually if you fertilize your tree, regardless if you use mineral fertilizer or organic fertilizer, watch for a complete fertilizer, which also includes micronutrients.
so here you do not need further micronutrients and the trees may go for a long time. Especially in many organic fertilizer sources a very good dose of micronutrients can be found, so adding micronutrients to the potting mix, by including some compost, pre-rotten manure seems very promising.
for all other: A addition of micronutrients to the potting mix seems a good idea, if the mix is more sterile and infertile.... but: It depends allways and how and which what you further fertilize the tree.

So, this discussion is also a discussion about philosophy, and discussion about philosophy are nearly endless.

So it's good to provide information, and let others decide.