I'm in Minnesota and I use black heavy Mississippi River dirt sediment type soil mixed with a full farm compost. I've experimented with different ratios. It's hard to give a citrus tree too much nitrogen in the soil but it is possible. Two to one is good. Soil to compost. I mix cypress chips to break up the heavy soil. Moisture retention with cypress is supposedly higher than other wood types. So it gives a wider window of moist soil between rain. We get good rain here but it drys out in different periods in the summer. If it goes dry for a few days or more and the Citrus are on a full sun deck when it's hot, then the plants won't dry out when the deck is baking with all the albedo. To me the guru of citrus is Ed Laivo. He says to use coir in the mix which is a coconut byproduct. In solid brick form, bust it into chunks and mix with the soil and compost. It retains h2o and oxygenates the soil. I'm going to try it next spring when I next repot. My motto is repot yearly and Jack up the soil as much as possible. I use

Any mulch is good, but be careful they you don't do shallow watering. That is what gets many people. They don't water deep enough to encourage the roots to grow deep nor enough to penetrate the mulch to give a good soaking to the roots.

If the roots gravitate upwards toward the mulch, then you are in store for a whole lot of problems..That is why many will put just a thin layer of it around the tree and never on the trunk. Many too will dig a gully around the the tree depending on how big it is, usually the perimeter of the tree line so that water will fill up the gully ensuring a good watering even under mulch.)

Mike

Indeed! I was using a thick dark heavy dense mulch (baileys moisture mulch) and beneath the mulch layer I have my dripline irrigation, it had been 12 months from when I had mulched using this, in the peak of summer the dark mulch had absorbed a vast amount of heat enough to roast the roots but lucky the layer was 100mm thick! Now heading back into spring here in Perth Western Australia I thought it would be a good idea to see how the mulch was going, surely enough the feeder roots had started growing into the mulch layer right up to only half an inch beneath the surface!!! Lucky for me I had gotten onto this fast before summer strikes!!! I have excavated the existing mulch layer out back to the original soil level, I had to bite the bullet and remove some of the feeders that had grown into the mulch layer but im confident they will recover quickly and long before summer hits! I have gone straight to a course chunky pine bark mulch, not sure if it's going to fix the problem but I'm confident the trees are getting a deep water and that the mulch had just got saturated in the winter from all the heavy rain, that and the fine dense material just made me think the baileys moisture mulch was great in summer until the winter rain had saturated it turning it into a rich dense field of goodies for the roots to go wild in, so in hind site Im telling myself I have essentially hurt the trees slightly by removing them feeders that had gone mad in the mulch but in the long run I have done the trees wonders from getting rosted in the coming summer! Fingers crossed for the course pine bark!