i was recently updating my garden notebook and making lists for fertilizers to buy this spring. i keep a list of my favorites along with what percentage of nutrients is in each kind. it dawned on me this morning that my azalea or "acid" fertilizer contained no sulfur. how can this be? am i totally dense or missing something here?
a question re: fertilizer
Sulphur is sometimes mixed in with other ammendments. In organic fertilizers, it could be included in some of the "meals" listed. Kelp Meal, for example, contains calcium, magnesium, sulphur and other trace elements. In chemical fertilizers, you can look for the word acid or sulphate, as in Sulphate of Potash or ammonium sulfate.
Other fertilizers add iron-chelated compounds which provide iron in a more soluble form that acid loving plants can easily absorb. In this case, they would need to add no Sulphur. Sulphur helps lower the soil pH which in turn makes complex forms of iron easier to absorb but, these iron-chelated compounds provide the "easier to absorb forms of iron" and thus would not need to include Sulphur. Chelated iron is usually sold in liquid form but is also available in powders and granular form.
i probably wasn't too clear in my first post. if a feed is marked "azalea, for acid-loving plants", shouldn't it contain sulfur? otherwise, the only thing that sets this feed apart from my other feeds is lack of sulfur and magnesium. it seemed backwards to me.
No, not really. You do not "have to have" Sulphur on azalea fertilizers. Azaleas/rhodies shrubs need iron more then they need Sulphur; no more than a trace of Sulphur is fine for most azaleas. They need Iron more but unfortunately, Iron can be difficult to ingest if the soil is alkaline. As a result, fertilizers try to provide iron using three approaches: (1) include iron-chelated products in the fertilizer; (2) add Sulphur; or (3) do both things.
The first approach does not affect the soil alkalinity but it provides the azaleas with iron in a chemical form that is easy to absorb. The second approach helps lower soil pH and this in turn makes the naturally occuring iron in your soil easier to absorb.
In my neck of the woods, the soil is alkaline so I add Sulphur this time of the year. As a matter of fact, I am doing that the next time it rains.
I should point out that I do not fertilize the azaleas though. Azaleas are not heavy feeders like roses and, generally speaking, established azaleas can feed off the decomposing mulch. Should a soil test indicate that your soil needs certain minerals, I would then add some cottonseed meal to the azaleas in Spring. When newly planted, you can add Mycorrhizal fungi to the azalea soil. For more information, see http://www.azaleas.org/azculture.html#fer
thank you for your detailed response. it is much appreciated. i was trying to compare my feeds and see what set the "azalea" or acid feed apart from the others. the few Rhodies i have are doing well and i just give them a light feeding after they bloom. they are practically in pure sand so i do mulch well and top dress with a good compost once in a great while.
You have rhodies over there? Oh wow! Nice! I cannot locally get any rhodies. While I wouldn't flinch buying mail order, I would prefer to buy them locally the first time. I have only run into one nursery that sold them here and it was over 20 years ago; they do not sell them anymore (they do sell azaleas of course). How did you obtain yours? Mail order, Internet or from a previous home?
a previous owner planted them at another house we own here. we dug one up, actually had to pull it out with a truck and then dragged it across the properties to the home we are in now. i didn't see how it could possibly live but it did. i really babied it for the first 6 months. i don't know its name though.
i put in a Southern Indica Hybrid Azalea last year, 'Little John' but if i ever see blooms, i will be surprised. they use them for foliage plants here and are just now becoming popular in our area nurseries. i don't have enough shade for any more...it's brutal here! lol
i will ask my local nursery if they can get rhodies and let you know what they say. they are a new nursery and have been very helpful in ordering things for me.
Our alkaline clay soil is not the place where azaleas and rhodies will prosper so a lot of preparation must be done when planting them. Usually that means planting on raised beds. But it has always been a little puzzling why the nurseries bring all kinds of azaleas (which of course are rhodies) and no rhodies. While azaleas are more floriferous, this lasts only 2-3 weeks and the foliage of SOME rhodies is prettier. I also love the rhodies with indumentum in their leaves (yaku hybrids). Oh well....
i agree. i never see rhodies, only azaleas. maybe the newer azaleas are more maintenance free for the majority of people.