If you can't drain it how about bringing in some good topsoil and making a raised bed. With a 5% grade and a raised bed I think Citation would do fine.

The Fruitnut

What you want, is to build is a dry well. It can be as simple as a buried trash can with holes in it, filled with broken concrete and then placed at the lowest drainage point. Or a network of French drains leading to the dry well. I have constructed a few, to drain areas on my property, and they have worked quite well.

http://www.richardcleaver.com/wp-content/uploads/2007/04/drywell.jpg

Something else that might help, is putting lime in the area to break up the clay, that will promote some drainage. I have also dumped sand in areas, to absorb the water, more to provide a surface that is drivable with a lawn tractor, than to make it plant-able. A word of caution, some clays turn to something similar to concrete when mixed with sand. Mine does not have the PH or chemical properties that make this happen, but yours may. So ask around or test a small area.

Best of luck.

>>> some clays turn to something similar to concrete
If there's hardpan in his area, he's probably heard it mentioned before by friends, family, etc. Which is possibly the cause of his drainage problem and will the stumbling block to burying the dry well.

Taking a step back....
If your drainage problem is mild or moderate, the citation stone fruits may do just fine without drains or wells. However, there are a planting methods you must choose from in order to keep it from a slow death in the clay soil.

For both mild and moderately problematic drainage issues, as suggested above, a raised bed (or large rounded berm) works wonders and is probably the best decision -- which is why I listed it first. But this does not fix drainage and the area will continue to flood in rain, though the tree will do fine if the bed is done correctly (allowing excess water to drain away from it) and is 18" or more.

For a mild problem, you can avoid the raised bed and dig out a hole 3x width of what you need, but only deep enough for the tree (probably 12"). Then dig a "mote" around where the tree will be planted, at least 12" deeper (more is better), creating a pedestal for the planted tree to "sit on". Back-fill all of what you dug out with 50% amended soil and 50% original clay. Then dig your planting hole, only large enough for the tree rootball (probably 12" across and 12" deep if in a standard #5 3.4g container) and ensure the tree is planted around 2" higher than the existing soil line, as everything will settle later. You can see a picture of this method on the back of nearly every plant or tree label at any big box store.

Do NOT merely dig a small hole for the tree and back-fill with quality amended soil. As the only area with fast(er) draining soil, this will act as a tub and water will be drawn IN to your tree's root area and flood it. That's the intention of the mote above, but it won't be large enough and therefore won't work in moderate to severe problems.

Now back to drainage...
If your problem is severe, which might be since you're considering a french drain, please allow me to share my experience.

I live in Fresno, CA and have a narrow side yard as well, which is standard design here for "track home" residential southern-facing side yards. It's about 15'x44' but it has the usual slight grade toward the road and is comprised of 3' and 9' long dirt strips separated by sidewalk. It's heavy clay, with hard-pan that started between 18" and 24" deep, and was a "drainage problem" anytime it rained.

In our desire to develop a small orchard in the 9'x44' strip, we decided to get some exercise and broke out the shovels intent on improving the clay soil with various bag amendments (such as Amend brand soil condition) . Once we hit the hard-pan, we decided to go ahead and break it apart and excavate. Long story short, the excavation project went a little overboard removing hard-pan and we had to bring in a couple cubic yards of soil to replace all that "cement" crud we removed. I rented an electric jack-hammer for $50, which worked well but was a bit heavy. I went ahead and purchased a cheapo electric "demolition" unit from Harbor Freight for $130. It was lighter and worked beautiful (though who knows if it'll ever work again).

We now have fantastic soil teaming with organic life with NO drainage problems where we excavated. We planted several peach & nectarine (on Citation) and orange trees using the High-density Planting approach of Backyard Orchard methodology. They are all doing great so I'm going to plant some apples and pears next. Across from the new mini-orchard, in the 3' strip, is the original lifeless heavy clay soil. It's flooded right now from yesterdays rain. A few hours ago I dumped out a full 50 gallon barrel of rain water (drainage problem on east side of house) into the orchard area where no trees are, and the entire amount drained away in less than 10 minutes.

My suggestion
If you live in this type of area with have heavy clay and hard pan below, see if you can create permanent drain cracks.

Dig as far as you can with your shovel in 3 different spots (doesn't have to be very wide) along that 30 foot area. If the deeper you dig, the harder the soil becomes, soon you'll hit the true hard-pan which no shovel or pick-axe can penetrate. Rent the jackhammer and break completely through it--you do NOT have to remove it like we did. Breaking through it will allow the winter rain water to drain below it to mother earth. The pan can be thin or thick depending on a number of factors. When I broke through mine, it was obvious as the jackhammer nearly "fell through the earth" into soft sandy soil.

Once completed it's OK to dig small holes for each tree and back-fill with quality amended soil (exactly what I said not to do above) using a 30/70 amended/original soil ratio. Plant trees between your new drainage cracks, not directly over them. Unless you excavated the pan, then it may not matter as the water should drain away fast enough.

I hope this helps you or any future readers who come across this post.

Thanks for all the good advice! I will check to see if there is hardpan close to the surface to poke through, and build a dry well. That will definitely improve drainage, but with continuous heavy rains we have on the northern California coast in winter, I still expect the area to be saturated / flooded for up to a week at a time. Would that kill the roots of trees?

If the roots are only flooded during the winter, you'll be fine. If the flooding goes into early spring, you'll notice delayed bud break, and the trees will eventually die.

French drains/field tile work well, but as you point out, you have to have a place to take the water.

Good luck.

A raised bed will keep your roots alive as will some large pots. 15-40 gallon pots would fit your area well and fruit trees do well on Citation in that size pot. Easier than a drain in my opinion.

The Fruitnut

If you don't want to break through the hard-pan or build a raised bed (best idea IMO), the approach using pots that Fruitnut described can be done using fabric containers sitting on your existing clay soil, like SmartPots (which come in huge container sizes like 200 gallons). They will help air prune automatically as you step up in container size and they are cheaper than regular containers. Not all that aesthetically pleasing, but supposedly offer the best root development by increased aeration, cooler soil temps, and excellent drainage on top of poor soil like ours.

I've recently purchased a few and potted but cannot personally attest to the above.