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when should i fertilize (confused) rhododendrons?

Posted by gammaray usda 9 (My Page) on
Wed, Sep 7, 05 at 19:04

hi, i have 3 rhododendrons that are at least 25 years old (they are about 5' x 5' each) that have not been looking very robust lately. some leaves are yellow with green veins. a few leaves are totally yellow. a few other leaves are shriveling up. i tested soil and it is slightly low in acid. nitro is extremely low. N P and K are also off. i want to fertilize them but the problem is that they are trying to bloom. it is odd because as i recall, they usually bloom in late winter/early spring only. they seem to be confused. i live in USDA zone 9 (northern california), and we had a very long winter and short summer this year, so maybe this is confusing them. normally, they would be fertilized this time of year. so, my question is : is it ok for me to feed them now or should i wait until they are done blooming ? also, to help the soil quality, someone recommended adding alfalfa. can i at least do that when they are about to bloom ? my 20 year old camelias are doing same thing and also need to be fed so i have same question regarding them. i am a beginning gardener and would appreciate advice on how to proceed. thanks !


Follow-Up Postings:

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RE: when should i fertilize (confused) rhododendrons?

If your soil is alkaline, your rhodies will sulk. If the soil is right, they just don't need much added fertilizer. Go to a good garden center and get something to acidify the soil (not too strong) and make sure there is lots of organic mulch for those shallow roots. If you have pine needles available, you can accomplish both ends with one product.


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RE: when should i fertilize (confused) rhododendrons?

Compared to plants like roses, rhodos and azaleas are not big feeders. And contrary to what fertilizer companies would want us do, the Azalea Society says that organic matter such as acidic mulch is fine and chemical fertilizers may not even be a good choice; just remember to add more mulch when yours has decomposed enough. See the link below:
http://www.azaleas.org/faq.html#fer
If you use chemical fertilizers in order to compensate for soil problems, I would suggest fertilizing in early spring; see the link below:
http://www.rhododendron.org/fertilizing.htm

To increase your NPK Soil Levels, try using some organic ammendments as they decompose slowly and last for a longer time period. In this order, I recommend the following items: 1. Organic Compost (found at Lowe's, HD, etc), 2. Cottonseed Meal (found at local organic stores), 3. Liquid Fish (has a little of all trace elements like magnesium, etc) or Liquid Seaweed (at Lowe's, HD, etc).

I do not recommend alfalfa at this time of the year because it has a growth hormone and you were concerned about long winters. Optionally and only if you know of someone who can give you some Epsom Salts and some Gypsum, I would give your rhodos' soil a one-shot-only of them until your next soil test next year; that will add some more useful minerals to your soil.

It is unusual but some types of azaleas & rhodos do bloom this time of the year. The Azalea Encore Series are one very common example but there are others which will do that as the summer temps go down. I am currently enjoying this reblooming period myself.

Iron Chlorosis: Greenlight Iron & Soil Acidifier is a product that I use when I am out of pine needle mulch (hard to find here and costs $10 a bale) or my alkaline Ph returns in full force. That product does not have any Nitrogen (NPK is 0-0-0) and, in late Fall or during Winter, it will not force the plants to grow new tender shoots that the winter might kill. I have seen it a big stores and local nurseries.

Regarding Camellias, I feed them some blood meal (high in nitrogen) in March; cottonseed meal or canola meal in May and July (lower nitrogen, higher phosporus & pottasium just before new growth buds begin to swell) and then bone meal in September (high on pottasium, good for the roots).

The above information on Iron Chlorosis also applies to camellias. For more information on fertilizing camellias, go to the American Camellia Website. The link below will take you to a webpage with information on Camellia Care:
http://www.camellias-acs.org/qanda/caring.asp

Hope that helps you, gammaray.
Luis


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