A: Proper applications of water for citrus and especially avocados can oftentimes make the difference between success and failure. As far as mound planting is concerned, citrus usually do not need to be planted that way. However, I would suggest mound planting a citrus if it is grafted onto “Flying Dragon” root stock which, because of its dwarfing effect reduces plant vigor enough to make it more susceptible to “root rot”.,
I almost always suggest the use of mound planting for avocados because of their inherent susceptibility to root disease. You can use a soil sampler(contact me to find out where to buy a good one) to check if the water is penetrating deep into the root zone. The sampler is made from a tee-shaped metal bar that has a cylinder at one end with a tapered tip thereby allowing you to easily take a core sample up to 36″ below grade. I suggest irrigating avocados thoroughly but infrequently.The idea here, is to leach out the excess salts present in our water supply.These salts would otherwise accumulate rapidly with the typical 5 minute a day automatic sprinkler system used for lawns.
Young avocados are very sensitive to the various salts present in our drinking water and as a result of the root damage that typically occurs from this salt buildup, the young plant usually dies. Keep in mind that well draining soil is also very important to the success of establishing a young avocado tree. Mound planting alone may not be enough. You should also verify how “well” your soil allows water to drain away. What is “good” water drainage for a avocado? Dig a hole 24″ deep and fill it up to the top with water and allow it to drain completely. Now fill it up again to the top but this time keep track of how long it takes to empty. Ideally, I would like to see it drain at a rate of 6″ per hour for avocados.
A final note… avocados and citrus benefit highly from a 3″+ thick layer of mulch such as organic compost, as both species have a dense network of fine feeder roots just below the soils surface.Good luck and have fun planting.
I did not mention, it but adding solution grade (powdered) gypsum to the soil surface at the rate of two cups for a 5 gallon sized avocado is very helpful in countering the ill effects of salt toxicity as well as adding a protective layer to the exterior root walls thereby making it more difficult for the root diseases to enter.