I live in an area with clay soils, low yearly precipitation (11 inches per year) and high water costs. I am recommending "standard" citrus rootstock to anyone with a similar situation, especially the last two variables above. Here's my argument:

1- "standard" rootstocks are more vigorous both above ground and below. Therefore a full grown tree should require less irrigation, all other variables aside. My neighbor has full grown navel and valencia orange trees that receive no supplemental irrigation and it put out some nice sweet fruit.

2- for people who are concerned about tree size, you can always summer prune to reduce both the size and vigor of the tree.

* I am obviously no expert (feel free to disagree in the comments below as I am actively encouraging an discussion) What is your take for in ground citrus rootstock?

So you are suggesting that a larger tree would use less water than a dwarf tree?

I assume you are talking about sour orange rootstock as opposed to trifoliate rootstocks.

Is this correct?

The amount of water a citrus tree uses depends on 1) the size of the tree's root system, 2) the amount of available water, 3) volume of foliage, and 4) the climate. Assuming the climate is the same for both trees, the larger the tree, the larger the canopy, and the greater is the transpiration flow from the leaves, therefore just due to volume larger trees use more water per tree. However, I would think the amount of water used by a tree, when based on a per square meter of leaf surface area, the water used would be the nearly the same for both a large or dwarf rootstock tree of the same citrus variety, and age. There might be a little difference depending on how vigorous the root stock. . - Millet (635-)

I think what he is saying that it would require less supplemental irrigation as the more vigorous growing root system would be larger and would take up more water than a smaller root system.

Of course, one would never prune a citrus tree just to keep the canopy smaller, unless there was no concern for the limited amount of fruit that would result. - Millet (635-)

It has long been known that pruning a citrus tree reduces the tree's ability to produce fruit (at least for a year). This is because citrus produces fruit on new wood, and the act of pruning removes the new growth. - Millet (634-)

It is well known with stone fruits (and others) that the rootstock affects how often one needs to water the tree in the summer. In our hot, dry California summers apples on seedling rootstocks need little to no supplemental water in loamy/clay soils. Dwarfing rootstocks, on the other hand, such as M27, need significantly more water because their roots are not nearly as extensive, deep or vigorous.

Also, pruning in these types of trees keeps them a manageable size and also induces branching at an earlier stage. I would imagine that pruning some of the more quickly growing branches would be balanced by the greater branching in terms of overall fruit production.

Some people also state that fruit quality is superior on non-dwarf rootstock earlier in the tree's life. Dwarfing rootstock actually restricts the resources to the tree, and it makes sense how that could reduce fruit quality. Probably later in the trees life, this doesn't make much difference.

-Brett

Chris wrote........"I would prefer to have many citrus trees (several varieties) that give me an edible amount (50-75 pieces"........

Chris, it is your yard, and your trees, you are certainly free to cultivate your tree any way you wish, there is nothing wrong with that, have at it. I think, 75 fruit would be a stretch from a small fully pruned citrus tree.

The best method of pruning a citrus tree, in order to maintain a small size, is to prune only one side of the tree per year. By doing so, the unpruned side will still produce its full crop. Then prune the opposite side the following year, letting the previous pruned side to produce its crop. This method maintains the desired size of the tree, while still getting fruit.

However it is getting off the topic which was water use by tree size. - Millet (634-)

Chris,

I see what you're getting at because I've considered the same thing for a while for mandarins and sweet oranges. Maybe my considerations will shed some light on your thoughts ... or anyone feel free to point out any flaws in my own logic.

Quote:

So it will have a larger root system and smaller canopy than a tree on dwarfing rootstock.

It sounds like this leads you to expect less supplementa irrigation is required for the tree in this circumstance. This is true, but only for a time. I understand the premise "expansive rootage means greater soil area is covered, thus more water availability when needed". But that is ignoring the "keep pruning to reduce vigor" affect has on the tree.

Would not a vigorous-stock tree with excess rootage (for the canopy) either push out more growth again or shed the "excess roots", attempting to bring itself back into balance?

You already realize given a tree in balance, pruning it will 1) reduce energy storage (citrus store more energy in their foliage vs. other fruit trees), 2) reduce photosynthesis capacity, 3) and stimulate more growth at the prune points. All mean less energy is produced/available and lower water demand on roots, but this encourages fine-root shedding. Exactly to what extent? I do not know, but I assume it's significant.

If a "dwarf sized" tree is a pre-requisite (i.e. ~10' tall for mandarins), it certainly can be done with vigorous-stock trees and doing so has strong early benefits. Whereas the lower vigor rootstock trees have weaknesses at the early ages. As was pointed out, once both trees are fully mature I also believe the differences are greatly diminished ... except for: 1) extra work continually pruning the standard tree, 2) creative pruning required to achieve equal amount of high quality fruit, and 3) an unusual freeze could outright kill the tree lacking the Trifoliate-hybrid (aka dwarfs) cold resistance. All three "cons" for the standards at maturity.

-- C4F