What sort of lime, lemon and mandarin have you planted? Washington naval oranges prefer a warmer climate than is generally available in Victoria (not that valencias like it too cold), mandarins prefer mild coastal conditions and lemons, well, they are usually a bit hardier than the other two but also like a 'Mediterranean' climate. There are 2 main or popular varieties, Meyer and Eureka. I think I heard somewhere that meyer performs better in the cooler climes, however, I planted a eureka some years ago in my mild to sub-tropical climate and it failed so I replaced it with a meyer and that's thriving. They all need a sunny, well drained position free of weeds or other growth and generally require feeding with manures or other fertilisers. They certainly do not like to be waterlogged. Subject to climatic conditions, on the basis of your description I tend to think it might be a soil problem. Might be an idea to take a goodly sample along to your local nursery and see if they can analyse it for you. Oh, and the only lime I use is dolomite, it's milder than garden or horticultural lime.

Hi, your advice and information is much appreciated! Can't remember what variety I bought, but will look into the Meyer as they sound a little more hearty. Thanks again.

How long ago were they planted? I can see two ... what's the shade-tree they are planted near? I see bluish flowers on the ground, is it a Jacaranda?

Yes, could be overshadowed by a jackaranda, and the roots of that could also be gobbling up the nutrients you've been giving the citrus.

b.

Apart from the possibility of root competition you have to be aware that citrus has a mat of near surface roots that has to be kept well watered and should not be cultivated.

The well watered bit could cause problems if drainage is not good.

I feed my Lemon and lime trees twice a year with a complete Citrus food.

The literature on the net suggests that soil with a fairly neutral PH is best. So as Funnelweb suggests in post 1 it might be an idea to have the soil tested.

This post was edited by arthurm on Fri, Jan 17, 14 at 18:14

A big thank you to everyone for advice. Yes there is a large jacaranda in the yard, and it does shade the citrus for some hours during the day, but they do get morning and afternoon sun. I will definitely do the soil test, and am starting to think - soil issue combined with shade is likely to be the key issues to my failed citrus.

And jacaranda have a notoriously spreading/shallow root system as well as the larger roots, to the extent that older ones can send buttress roots out and kill off competing lawn. I think the root interference with the citrus (which hate that, as has been said) is probably more significant than the shade issue. Plus the jacaranda robbing the citrus of the nutrients and water. Only from the one yard shot, and it's only a suggestion as I don't know the directions, but I'd be inclined to move the citrus over to the back of your veggie patch area, but plant them in mounds as they do enjoy a bit of elevation for good drainage and then you can mulch them. The translocation into a hotter sunnier spot would need some protection for a couple of weeks - a bit of a temp shade barrier to stop the leaves burning while the root system recovers, and extra water.

Well if you do move them, I'd cut back them back by at least a third, that'll reduce the shock to the plants - cut back to a node so as to prevent dieback.
By way of observation, I had my jacaranda removed by tree removalists and hired a stump-grinder to grind out the stump. When that was done, I overplanted with Allamanda cathartica - back in spring - and, whilst I was concerned I was planting the allamandas too early, that is into soil heavily impregnated with jacaranda root mulch, they have actually thrived!

looks like getting too much shade and competing with those other trees.fruit trees love full sun and they don't do very well next to other trees