Whenever see directions given for fertilizer application, they always specify so much of this or that, depending on the age of the tree. I've bought all of my trees from a nursery and I really don't know how old they are. Some were 15 gallon trees that are about 4 feet tall and have a trunk about 1-1/2" to 2" thick and a couple were 5 gallon trees that are about 3 feet tall and have a trunk between 3/4" and 1". How old can I expect them to be? These are various, Navel, Blood and Valencia oranges.

Thanks, Jeff

If they are in containers, you need to fertilize according to the size of the container, not the age of the tree. If you have just planted these in the ground, I would treat them as 1 or 2 yr old trees.

If you intend on keeping them as container trees, fertilize them at 250 to 300 PPM nitrogen a MINIMUM of once a month, twice a month would be much better. As Skeeter wrote, if you plant them in the ground, due to the limited size of their root system, count them as one year old trees.

1 year old in ground tree fertilize 6 times a year equally spaced out.
2 year old 5 times a year
3 year old 4 times a year
4 year old trees 3 times a year
5 + year old trees 3 times a year

For trees 3 year old and younger do not use a fertilizer with higher than an 8 percent nitrogen content (6-6-6 or an 8-8-8 fertilizer). On 4 year old trees you can use either a 8 or 10 percent nitrogen fertilizer (8-8-8 or 10-10-10 fertilizer) 5 year old trees and older you can use up to a 11 to 14 percent nitrogen fertilizer. In your area do not fertilize in ground trees after September and the end of February. - Millet (1,097-)

Thanks guys. The trees are all in the ground and most of them have been for 8-10 months. So it's the age of the root system, not the actual tree age that I should be concerned with?

I'm still curious how long it would have taken these trees to attain this size? I would have guessed two or three years but I just acquired another tree which has a label saying that it was planted in June of 2008 and it's still only 10" tall.

Jeff

Many citrus trees when planted in the ground are 1 year old nursery trees, which of course start out as a 1 year old tree, either container or bare root. After they are planted the root system of these trees start to grow larger from day one. However, a containerized tree's root system is restricted from growing larger by the container, no matter how old the tree is, unless it is transplanted into an ever larger container. A common rule among quality nurseries, is at the end of a year the tree is either transplant into a larger container, sold, or thrown away. Of course, some nurseries don't abide by this rule, then their customers get a root bound stunted tree. Most one year old properly grown nursery citrus trees are two feet tall. - Millet (1,097-)