Carol,

Oops. I'm sorry, I meant to write a paragraph about micronutrients in my original answer to your container tomato-growing tomatoes and then I forgot to do it. The quick answer, though, is that your plants probably will get all the micronutrients they need if you use organic fertilizers, and the addition of a micronutrient powder is not absolutely necessary.

Here's what you need to know about plant nutrition in general, and specifically, a few facts about micronutrients.

PLANT NUTRITION: There are basically two kinds of nutrients that plants need to grow: nonmineral and mineral.

NON-MINERAL NUTRIENTS: These are found in the air and in water: hydrogen (H), oxygen (O), and Carbon (C).

MINERAL NUTRIENTS: These fall into two basic categories--macronutrients and micronutrients.

MACRONUTRIENTS: Macronutrients fall into two basic categories.

PRIMARY MACRONUTRIENTS: The primary macronutrients are what we think of as the big three: nitrogen (N), phosphorus (P), and potassium (K) and are often added to soil because plants use a LOT of these for growth and survival, thus depleting the available supply. These are easily found in all kinds of fertilizer, whether you are using chemical or organic fertilizers.

SECONDARY MACRONUTRIENTS: These are calcium (Ca), Magnesium (Mg) and Sulphur (S). They are usually found in the soil in adequate amounts. If you add lime to your container mix, you are adding calcium and manganese. If you are using organic material, like compost in the container mix and then grass clippings or chopped leaves for mulch, you are adding sulphur.

MICRONUTRIENTS: These are elements that also are essential for plant growth but which are needed in only very small amounts. When I was younger, we used to refer to these as "trace elements". For these to be readily available for easy uptake by the plants, not only do the micros need to be available, they need to be available in the right ratios to one another. An excess of any one of them can adversely affect the others. Micronutrients usually are found in soil.

The micronutrients are boron (b), copper (Cu), chloride (Cl), iron (Fe), manganese (Mn), molybdenum (Mo) and Zinc (Zn). In most cases, especially in soil that has compost or mulch made from chopped or shredded leaves, these micros are present naturally. Or, if you mulch your containers with grass clippings or shredded leaves, they will automatically provide your soil with the micros as they decompose.

When you are planting in well-prepared, well-amended soil in the ground, you most likely have all the micronutrients your plants need. However, when you mix up a good soilless mix for containers, you may need to add a micro-nutrient powder to ensure the plants' nutritional needs are met since, technically, your growing mix does not contain soil. Some people who make their own soilless mix choose to add a micronutrient product to ensure all the micros are there, but it isn't necessarily a requirement that you do so. If you know that you have put lots of organic material in your mix, you probably have the micros covered.

If you want to add micros, there are several ways to do this, and using a micronutrient powder is just one of them.

Commercially-available micronutrient powders were originally developed for the hydroponic industry where their use is common in fertigation systems. Some people also add them to containers and even to their soil if they feel it is lacking in micros. But, unless you have a greenhouse supply store or garden center near you that caters to the hydroponic trade, it may be impossible to find micronutrient powder. STEM is one of the micronutrient powders, but there are many, many available. Some growers, especially non-organic ones, like to use these products because they contain micros in the proper ratios.

Remember, though, that if you are gardening organically, it is likely that most of the micronutrients your plants would need will be available via your use of compost and various organic fertilizers.

One reason I like to use the Espoma brand organic fertilizer products (Tomato Tone, Garden Tone, Holly Tone, etc.) is because they contain the necessary micronutrients in proper ratio to one another and I don't, therefore, have to add a separate micronutrient product. Also, many commercial fertilizers now have micronutrients as well as the big 3 (N-P-K), and it is usually mentioned on the front of the bag.

Hope this info helps.

Dawn