
1.) What should I use?
2.) When should I use it?
3.) How much should I use?
There are many many fertilizer options available, but I choose to use MicroLife 6-2-4 for the trees in containers, and cottonseed meal for everything else. MicroLife 6-2-4 is a great all-round organic fertilizer. Cottonseed meal isn't purely organic (lots of pesticides are used to raise cotton), but it's cheap, and it has just as much available nitrogen as MicroLife (cottonseed meal has an NPK ratio of 6-2-1).
I buy both from Hieden Feed on Stuebner Airline Rd. This weekend I picked up two 40 lb sacks of MicroLife 6-2-4 for $24 each and four 50 lb sacks of cotton seed meal for $16 each, for a total cost of $112 (Call Hieden Feed for current prices!). That may sound like a lot of money to spend on fertilizer, but that's actually really cheap considering I have 50+ trees and plants. It would cost me much more than that to use a chemical fertilizer.
There are lots of varying (and sometimes conflicting) guidelines on when to fertilize, but I like Texas AgriLife Extension agent Monte Nesbitt's advice the best. He advises fertilizing citrus trees three times a year, with 60% of the total fertilizer being applied on Valentine's Day, 20% applied on Mother's Day, and the final 20% applied on Father's Day. I like this because it's easy to remember, but unfortunately it assumes you're using an ammonium sulphate fertilizer with an NPK ratio of 21-0-0. Unlike ammonium sulphate, cottonseed meal and MicroLife are slow-release fertilizers that work over a couple of months, so I'm going to try fertilizing a month ahead of Mr. Nesbitt's schedule to compensate, and hope that this ensures that the nutrients are available when the trees need them.
Finally, in order to figure out how much fertilizer to use, you have to do a little homework. According to Mr. Texas, citrus trees need between 0.3 lb and 1.4 lb of nitrogen each year for citrus trees, depending on their age (see table below for details). Both MicroLife and cottonseed meal have approximately 6% available nitrogen, so if I need to give a mature tree 0.6 lbs of nitrogen annually, I need to give it 10 lbs of total fertilizer each year (0.6 is 6% of 10), or 6 lbs in January, 2 lbs in April, and 2 lbs in May.
I weighed out equal volumes of both MicroLife and cottonseed meal, and for both two cups of fertilizer weighs about 0.5 lbs. Based on the nitrogen requirements, the recommended application schedule from Texas A&M, and the approximate density of the fertilizer, I calculated how many cups of fertilizer to use per tree during each application.
Tree Age 1 2 3 4 5 | Annual N / Fertilizer (lbs) 0.3 / 5 0.6 / 10 0.9 / 15 1.0 / 16.6 1.4 / 23.3 | January-February (60%) 3 lbs / 6 c 6 lbs / 12 c 9 lbs / 18 c 10.2 lbs / 20.4 c 14 lbs / 28 c | April-May (20%) 1 lb / 2 c 2 lbs / 4 c 3 lbs / 6 c 3.5 lbs / 7 c 4.7 lbs / 9 c | May-June (20%) 1 lb / 2 c 2 lbs / 4 c 3 lbs / 6 c 3.5 lbs / 7 c 4.7 lbs / 9 c |
I use a two quart pitcher with graduated cup measurements marked on the side, so it's really easy to give each tree the right amount of fertilizer, although I'll admit to erring on the side of too much rather than too little. That being said, with slow-release organic fertilizers like MicroLife and plant meals, you don't have to worry about applying too much and burning the roots like you do with chemical fertilizers.
I've got a lot of trees and plants, and I just can't keep track of a separate regimen for each kind, so I feed them all with the same fertilizer, on the same schedule, and in the same proportional amounts. I know this is lazy of me, but it seems to be working. The only real deviations from this system are that I don't fertilize the pear trees (vigorous new growth is susceptible to fire blight), and when fertilizing my blueberries I add 1 tablespoon of powdered sulfur per plant to help lower the soil acidity. So far this system is working pretty well for me. Leave a comment and let me know what works for you.