I know the recommended fert type, but I have no idea how much to use. Back-of-the-box instructions are vague, or geared for other outdoor plants where I am using it in potted citrus.

Is there some rough formula for determining how much fert to use for a given tree size, age, or soil volume? I've been trying to err on the side of caution, and do very low concentration foliar sprays on new leaf growth in addition to fert in the soil.

I apply fertilizer to containerized citrus trees at 300 PPM N. I started this amount of fertilization after visiting the Citrus Clonal Protection Program's (CCPP)greenhouse at the University of California. The CCPP fertilized their containers (large and small) at 300 PPM N with each watering. During the summer months I fertilize every time I water. All of my trees are growing in a 4:1 CHC peat moss medium. - Millet (1,251-)

Thanks Millet, so I guess quantity of water+fert doesn't matter much as long as all the excess pours out the bottom?

I have granular time release fert right now so I don't really have a good way to match this, but I will try to find some of the recommended granules soon here and switch to that.

What I actually do, is dissolve 246 grams of 25-5-15 W/TM fertilizer into each 55-gallon drum of water that I have spread throughout the greenhouse (6 drums) This makes 330 gallons of fertilizer solution at 300 PPM nitrogen. I also add Epsom Salts to each drum. I make 6 drums so that I only have to carry the fertilizer solution a small distance. - Millet (1,250-)

Millet, what concentration of epsom salt do you use? Thanks.

-Brett

Maybe around 80 grams. On the Epsom Salts, I really don't bother to measure it. I just sort of eye-ball it. Approximately 20 percent of the fertilizer. - Millet (1,250-)

I'm sure to make a mistake some where:

> 426 grams (426 g = 15.1 oz) of 25-5-15 W/TM fertilizer into each 55-gallon

426g of 25-5-15 gives 106g of N. Dissolved in 55gal=208l gives a solution of 106g/0.208m3= 510ppm.

Sylvan wrote....."I'm sure to make a mistake some where:" Thanks for your concern, I appreciate it. However, I rechecked the figures and 246 grams is indeed 300 PPM. - Millet (1,238-)

Millet, in your first post you swapped two digits and wrote 426 instead of 246. I did the calculation using precise conversion factors and came up with 249.7g of fertilizer in 55 u.s. gallons of tap water at 20C so the difference is insignificant.

jrb, thank you I see, as you pointed out, that in the first post I accidentally transposed the figures. I have corrected them. Sylvian, of course, was using my transposed figures in his calculations. Even when reading Sylvian's post, the transposed figures still did not click. Appreciate both you and Sylvin. 246 is the correct amount I use in 55 gallons. - Millet (1,238-)

OK, it works.

Most slow release fertilizers have at least two application rates. One rate for plants having normal nutrition requirements, and a higher rate for heavy feeders. Citrus is a heavy feeder, and requires the higher rate. Osmocote shows both rates, I don't know about Dynamite. Further *IF* (and it probably is) Dynamite's slow release 18-6-12 is formulated to match their competitor Osmocote's 18-6-12 than you might want to either use a different formulation, or also use a water soluble fertilizer along with it. 18-6-12 was formulated to be used when planting seeds. At least Osmocote 18-6-12 was. 18-6-12 has an EXTREMELY slow initial release, with the majority of nutrient release at the end of the release time. This is to coincide with a seed's germination, needing little nutrition upon germination, but more and more as the seedling grows. - Millet (1,237-)