Question
When purchasing fertizer, recently, I intended to buy 6-6-6. The store had 6-6-6, 8-8-8 and 10-10-10 with all three about the same price (actually a little cheaper for the 10-10-10).
Is there any reason not to pick the 10-10-10?

Answer
Hi Ken,
Generally there is no reason not to go with 10-10-10. As you probably have figured out, the important thing is the INTERNAL RELATIONSHIP between the 3 numbers (and not the size of the numbers themselves) which is important.

E.g. a 5-10-10 can be used just as well as a 1-2-2, a 10-20-20, or a 6-12-12 fertilizer. If you are supposed to apply 1 handful of 10-20-20 then you should use two hand fulls of 6-12-12 (roughly) and 10 handfulls of 1-2-2, however.

If you are advised to use a 5-10-10 fertilizer, then a 10-20-20 would also work, but a 20-10-10 would not. But you have probably figured that out already.


In your case, you can buy the 10-10-10 and just apply "half strength". E.g. if your instructions were to apply 1/2 cup 6-6-6 per plant, then use 1/4 cup 10-10-10 instead. "10" means 10 percent and "6" means 6 percent. So a 10-10-10 is almost twice as strong as 6-6-6 (or 6-6-6 is a diluted version of 10-10-10).

If you are just sprinkling a bit around each plant then it is sometimes safer to use 6-6-6 especially around plants which do not like much fertilizer to begin with rather than 10-10-10, but with a bit of careful attention this seldom becomes a bit problem.

One thing you can do is to check the lable for active ingredients. Sometimes there are differences. E.g. one bag may be based on UREA as the active nitrogen ingredient whereas another may use AMMONIUM NITRATE. Ammonium Nitrate release quicker in cool soil and is particularly good for early spring fertilization. If you have a choice, always go for ammonium nitrate (over urea products) if you plan to use it early in spring. In summer, with warmer soil temperatures, UREA is just fine.

However, besides the above example, you can safely choose any of the products (based on price) and simply make small adjustments to the amount you use.

-- Kenneth