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I'm looking to buy fertilizer for my camellias. I read on a couple of websites to use 8-8-8 or 10-10-10, but when I search online many brands sell fertilizers for camellias that have different compositions, sometimes as low as 4-4-4.
What is the difference? I understand it's the amount of nitrogen, phosphorus and potassium, what I am wondering is what will be the difference? Does a 10-10-10 fertilizer mean it has a higher concentration and hence I should use less?
Thanks
It's quite difficult to give a straight, simple answer - fertilizers are formulated differently in terms of how quickly they break down, so liquid formulations will be almost instantaneous, whereas a granular or capsule form may take up to six months to dispense its load of fertilizer, with other granular formulations lasting 6-8 weeks. This might explain the difference between some of the fertilizers you've looked at - the long lasting capsule types usually do have higher levels of NPK because of the slow breakdown time.
So yes, the higher numbers do reflect higher levels of fertilizer, but whether you use less or whether the difference is simply because of the formulation, it's hard to say without knowing which specific products you've been looking at. If your Camellias are in pots, then fertilizing is probably a good idea, but if they're in the ground and growing in good soil, it's not essential anyway, unless they're not coping with an infestation or infection very well. The other thing I'd say is, if you're in the Northern hemisphere and fall/winter approaches, now is not the time to give fertilizer, it should be applied in spring, as growth begins. Note also that there are fertilizers available made specifically for acid loving plants like Camellias, and these can be quite useful if your soil is neutral.
Yes. The numbers is the content of fertiliser (N, P, K) in percent. So a 4-4-4 means 4 kilograms of N, 4 kilograms of P and 4 kilograms of K on a 100 Kg bag.
The absolute numbers are important if one need to fertilise large surfaces, e.g. with norms and analyses, I know that I need 70 Kg of nitrogen per hectare (and year), so I can calculate easily.
But as wrote by Bamboo, the exact formulation is also important, some compounds are very slow to give assimilable substances, so one could fertilise (a single substance, e.g. Mg) every 2 to 4 years without "over-fertilising", other fertilisers could be too acid (or or basic), etc.
You are right - as others said, bigger numbers mean more active ingredients in a given weight of fertilizer. Since the proportions are the same for both (10-10-10) and (4-4-4) the two are interchangeable, but you need to apply 2 1/2 times as much 4-4-4 to give the same "dose" as the 10-10-10.
For "amateur" use, relatively weak formulations can be easier to use, because you don't have to measure out and work with very small quantities, and you are less likely to "burn" an individual plant by applying too much if there is uneven distribution of the fertilizer.
On a commercial scale the reverse applies - nobody is going to want to handle 25 tons of 4-4-4 material when 10 tons of 10-10-10 would do the same job, and is perfectly safe for the plants if it is applied accurately using the correct tools and machinery.
How fast the fertilizer is released into the environment is a completely different issue, and (in general) that is independent of the concentration of the active ingredients. For a given formulation, "all" the active material in whatever "dose" you apply will be released in a fixed amount of time (which might be anything from a few hours for a liquid foliar feed, to a year or more for long-lasting soil conditioner). Of course, the plants may not be capable of using everything that is available if you apply an "overdose", and the excess amount may damage the plants.
