Hi Everyone,I have several citrus trees in pots.They are young trees and
not holding fruit yet.I mixed in osmocote plus at planting.It has what i think should be the perfect blend for a slow release fert=
NITROGEN 16%(nitrate nitogen 8.5 per cent,ammoniacal nitrogen 7.5%)
PHOSPHORUS 3.5 %
POTASSIUM 10 %
TRACE ELEMENTS=
SULPHUR 2.4 %
MAG 1.2%
BORON 0.02%
COPPER 0.05%
IRON=sulphate and chelate =0.40%
manganese 0.06%
moly 0.02%
ZINC 0.015%

Correct me if i am wrong but this is very close to millets 5-1-3 ratio.
However,finding a soluble food close to this has proved impossible in
nz. However,i have "Miracle Grow" tomatoe plant food which comes close.
Millet do you think this will be ok=
NITROGEN 20 (urea 2%,monoammonium phosphate 5%,potassium nitrate 13%)
PHOSPHORUS 2.2%(monoammonium phosphate 2.2%)
POTASSIUM 9%(As potassium nitrate 9%)
TRACE ELEMENTS
calcium = 5%
magesium=0.5%
iron=0.16%
copper=0.07%
zinc= 0.06%
boron=0.03%
manganese=0.02%
moly=0.002%

Does this sound like a good soluble feed for occassional use?
Thanks for any advice

The ratio is 10-1-4.5. For me, that's close enough for my trees.

Both the fertilizers you mentioned won't dissolve easily into the water, though. So they are not that soluble compared to ammonium sulfate.

I have been buying a one year slow release fertilizer from the Crystal Company of Saint Louis that has a formula of 23-4-8 with trace minerals. This would be basically a 6-1-2 ratio (as close to the 5-1-3 thatI can find in a slow release fertilizer. Because it is a one year slow release fertilizer (actually it will probably only last 7-8 months in a warmer greenhouse) it gives off nutrients quite slowly, and helps to keep a minimum nutrient level in the container at all times. I also feed with a water soluble fertilizer that contains trace minerals. By the way, Laidbackdood, how is your tree doing that had some transplanting problems? Also, I believe that IN GROUND citrus trees are really not all that fussy about the nutrients that they are given. Commonly in ground trees are fed with 6-6-6, 8-8-8 or even a 10-10-10. However, for CONTAINER trees I have always believed that it is important to feed as close to the rate of absorption that citrus roots take nutrients into the tree. - Millet

Hi Guys,thanks for your replies.The osmocote plus slow release is specially
formulated for trees,shrubs and citrus and feeds for up to 6 months.It
seems right to me.
I also have some "thrive soluble food" with an N.P.K of 27/5.5/ 9
with 7 trace elements.Again i thought this was good until i found that 21.4% of the nitrogen was from urea.I am mindful of p.h too.
Millet,i have a few questions
1.Do you think that the osmocote and the miracle grow tomatoe food as
mentioned in the last thread would be good?They both looked good 2 me.
2.The above fert sounds good to me but you dont like urea,why is that?
The transplant problems you mentioned before was when i transplanted
a tangelo into a chc /coir combination.At first i had some leaf drop but
that stopped.I have since fertilised with slow release fert.The leaves look
pale green and there has been no new growth.Seems to have gone dormant.
However,it hasnt died,so i have hopes for the spring.My navelina,vainiglia
orange and grapefruit are all showing new growth in a good quality
container mix made of bark,water retaining agents,grit and added coarse
river sand by myself.Drains well.
I havent given up on chc/coir but my success has been in keeping this container
mix on the moist to dry side.Finger in soil method,now using the wooden
stick method too.Cheers

Laidback I think both fertilizers are OK. The tomato plant fertilizer's sources of nitrogen are composed of monoammonium phosphate, and potassium nitrate, both of which are water soluble, plus a small amount of Urea which is also water soluble. Your second question, Urea as a nitrogen source is fine IF it is a pure grade urea, meaning that the biuret, which is an impurity in urea fertilizers, has been removed. Citrus is more sensitive than most crops to biuret. Biuret that is present in some Urea fertililzers is created by excessive heating of chemical reactants during urea manufacture. Toxicity can result from urea that has an elevated biuret concentration. If urea is used as a nitrogen source for citrus, it should contain not more biuret than 0.25-0.45 percent by weight. The symptoms of biuret toxicity is an irregular, butter yellow chlorosis that starts at the leaf tip. Young leaves are more vulnerable than old ones, and affected leaves do not re-green. In your tomato fertilizer the nitrogen content from urea is small, giving 2% nitrogen, which means that actual urea content is about 4.5 percent of the product. However, should be fine, just keep a look out for any biuret symptoms on the leaves. By the way, what is the winter low temperatures that Auckland normally receives on adverage? Take care. - Millet

The one comment I would add, concerning urea, is that you have to be careful with your watering program. If you irrigate until water drains freely out the bottom of the pot, you'll need to stop doing that for a period of days after each fertilizing with urea, because

1. citrus trees can't absorb urea through their roots (they do, through the leaves)

2. Therefore, urea in the soil must be converted to ammonium by ammonifying bacteria. That's not a problem -- they're always there; however, the process takes time (days to weeks, depending on soil temperature -- warmer is faster).

3. As long as it is still in the form of urea, it is not attracted to cation exchange sites, so it leaches freely through the soil with mass-flow movement of water.

So, if you use fertilizer with a significant portion of its N as urea, it is important not to wash it away before it gets ammonified.

excellant information chaps!I was aware that urea was slower acting.
The maximum biuret on the thrive is 0.4%.
We are in the middle of winter here but Auckland doesnt get as cold as
down south but it rains nearly every day. Temps in day vary from 11 to
14 c and at night between 5 to 10c. It tends to be mild when it rains
I keep my plants out of the rain but they can still get sun if it comes out.
The weather tends to fluctuate here.I water once a month with food!
I believe my previous plant deaths were due to soggy soil. I try to keep the
top half of the mix reasonably dry because i read that citrus keep most
of their roots there in pots .cheers

Malcom Manners, very good information, one can alway learn from your postings. Thank you, I always look forward to them. - Millet

Very informative stuff here. I have a 24-8-16 soluble and says nothing about biuret so I feel good about that. It says:
3.1% ammoniacol nitrogen
1.2% nitrate nitrogen
16.1% urea nitrogen
0.9% Other water soluble nitrogen *
2.7% water insoluble nitrogen *
*contains slowly available nitrogen from ureaform (whatever that means)
Are these all good source of nitrogens? Will they be absorbed by roots or should I also spray leaves? Thanks