I have been wondering. Every other tree type out there enjoys a good heavy mulch under it. Mulch enriches the soil as it decomposes, keeps away weeds, keeps a relatively steady moisture level. All things great for other trees. So with all the benefits provided why is it common wisdom not to add mulch to citrus trees? Obviously not touching the trunk itself but wouldn't nice ramial mulch be a good thing for citrus as well?

I found a guide on Australian organic citrus guide on the organic page here which forces me to ask further about this as this guide seems to follow several similar guides I have seen on growing other fruit types and the use of mulch. Here is a quick quote which seems to contradict everything I normally hear about mulch and citrus.
"Mulch is used by many organic citrus producers to suppress weed growth,
conserve soil moisture and protect the soil from temperature extremes. A
benefit of using organic material as mulch is that it adds valuable organic
matter to the soil as it decomposes.
The benefits of mulch can often be observed in a relatively short time and
include increases in activity of earthworms and other organisms, water
infiltration rate and soil moisture retention, and reduced soil hardness.
These benefits, together with a moderation of soil temperature and
increased organic matter levels, help create soil conditions that are more
favourable for biological activity including tree root growth. This is
especially useful in citrus with its many shallow feeder roots."

The issue with mulch is, of course, water retention, and the potential for root rot. And I imagine whether mulch is appropriate depends on the circumstances to some degree - the soil conditions and rootstock among them. Many of my trees are planted in areas of the yard that are mulched either through natural leaf fall or through the addition of leaves that others have kindly raked and bagged and left by the curb for me. These trees are on a slight slope, the soil drains well, and the trees are not irrigated - they get watered only to get them established and then during bloom and under severe drought conditions. They are on Trifoliate or Swingle, which are two of the rootstocks whcih are more resistant to phytophthora. In these spots, I just keep the mulch cleared from within about a 12-18 inch radius of the trunks, and lighter, but still present, over the entire estimated root area for the citrus and I've seen no ill effect.

However, my parents also have some trees at their house. The soils there, in general, have a higher in clay content and do not drain as well. Last summer the folks who cut the grass just let it pile up around the base of the trees. Well, once I didn't make it up for about a month and they had not only let grass pile up, but they had set up sprinklers. Most of the trees were still okay, as it was during a dry spell, but the one tree that was in reach of the sprinklers - a little Page - was on the brink of death (and did, in fact, die). The effects of root rot were also plainly evident on a Sour Orange rootstock and on a Rough Lemon rootstock (neither good choices for around this area due to cold intolerance and susceptibility to phytophthora, but I was told they were on Swingle and Trifoliate, respectively, and only found out otherwise from rootstock sprouts).

I am in the process of re-bedding most of my trees(as in of all types, not just citrus) as I put in an irrigation system. Not planning on running it often but at least its there if I need it in very dry periods which we get on occassion(if they would just run their tap roots down about 6 feet it wouldnt be an issue). I am widening the beds to a five foot or so distance. Most of my soil is sand. I am leaving a clear area about a footish wide with pebbles in the center. But further away where most of the feeder roots are in the fungal duff zone area I am placing fresh ramial mulch to try and change the soil a bit.

I use mulch on all of my citrus. I have never had any issue with it, although I do live in california with very dry summers. I water with a drip system once per week for established trees and twice a week for young trees. It has worked well for me.

-Brett

My understanding is that the "no mulch" rule was for areas that are wet or that have problems with citrus staying too wet. That certainly is not the normal problem where I am in SoCal.

I brought in 20 yards of mulch and it has dropped my water needs by a large amount.

I have one area where my uphill neighbor removed his citrus trees and replaced them with a manicured back yard with lots of walkways, etc. He runs his sprinklers too long and water flows through the drain slots in the block wall. I simply use very little mulch in that area so that the water flows past and is held by the thicker mulch on the downhill side of the first row of trees.

I installed a ring of edging around each trunk so the mulch can not contact the trunk. I hope I'm doing this right but so far it seems to be working well. Please let me know if anyone can think of any issues with this.

There is a difference between commercial groves and back yard trees. However, it is generally accepted that organic mulches are not recommended because of the incidence of foot rot disease in citrus. In large groves, the best grove floor conditions for reducing frost hazards is bare, firm and moist soil. The sun hits the soil and re-radiates the heat at night, warming the air. Tall cover crops are worst because not only do those plants not hold much heat, but tall cover crops raise the level of cold air (cold air sinks), increasing frost damage potential. Whatever one decides for their own back yard tree, NEVER let a mulch touch the trunk of the tree. - Millet