2 Citrus Questions

I have 1 Meyer lemon, 1 inherited (not sure of the variety) navel orange, 2 Grapefruit and 1 lime tree.
The lemon, orange and 1 of the grapefruits were transplanted from tubs to the garden about 5 -7 years ago. The rest have been purchased and planted in the last 2-3 years. All of these trees are in close proximity to each other in the same type soil, with basically the same amount of sun and water.
We have heavy clay soil which has been amended, but remains clay-like, winter only rains (San Francisco East Bay,Northern California), very little frost and occasional hot days in the summer.
My questions are: 1. All the fruit except the lemon and lime produce extremely thick skins-1/2 to 1" thick.
2. The fruit (what little there is after getting through the skin), is less sweet than I would prefer, especially the grapefruit. (These are NOT red or pink, but theya re still pretty tart.) The lemons are quite sweet.
I would like to know what I can do to improve the fruit and make the skins much less thick so I will get more fruit. Water more or less? Give them added nutrients?
Any suggestions would be appreciated.
Thanks

The thick rind is most likely the variety. But it can also be exacerbated by over fertilization.

While some citrus varieties do have a thicker rind, there could be a fertilizer problem as well. This link contains a discussion of fertilizer as being the potential source of the thick rind problem.
http://www.ubcbotanicalgarden.org/forums/showthread.php?t=11769
What kind of fertilizer are you using on your citrus? Are you using citrus fertilizer? How often do you fertilize?

While the trees may grow in your area, not all citrus are recommended because certain varieties need hot summers to sweeten the fruit. Both Sunset Magazine and Ortho have published great paperback books on citrus which include whether they are suited to certain areas. Four Winds Growers Nursery in Fremont, growers of dwarf citrus, has a link to a chart that shows whether a certain variety needs heat to sweeten. If that is the case with your trees, there is nothing you can do to sweeten the fruit. You can continue to grow them as ornamentals or yank the sour ones out and plant citrus that don't need the heat or as much heat. You might try contacting Four Winds for more information.
http://fourwindsgrowers.com/solver/varietyinfo.html

I just got back to Dave's Garden so i will try to continue this thread.
I fertilize with a Citrus/Avocado fertilizer. I usually fertilize only once a year, maybe twice.
Should I be fertilizing more? I only water in the summer and then only once a month (as I said we have CLAY, CLAY, CLAY.) It is difficult to dig in this soil more than a few inches if it hasn't been heavily watered.
I have been told that to rectify thick skins you need to apply 250g of sulphate of potash in early summer and a further 250g with 1kg of super-phosphate in autumn. Then next spring apply 1kg of complete fertilizer.
Does this sound right?
I'd hate to give these babies the wrong thing!
Thanks for the help.
GPGruver

The general rule for fertilizing citrus trees is to take the recommended yearly dose and divide it into three evenly spaced applications. The dosage depends on the size of the tree and the fertilizer you are using. Sometimes the amount to use is given in pounds of the actual nutrient needed and you have to figure out how much of that specific fertilizer to use. Make sure the citrus/avocado fertilizer contains all the micro-nutrients citrus trees need. I'm leery about adding large amounts of supplements without knowing if they are really needed. Getting the soil tested would be a good start before adding the potassium sulfate and the super-phosphate. Check the nutrient levels as well as the soil pH. If the soil pH is off, the trees won't take up the needed nutrients even if they are present in the soil. Also, a nutrient in excess may affect what is taken up by the roots. Too much of a good thing can be very damaging.

A potassium deficiency usually results in smooth thin rinds in addition to other symptoms.
http://edis.ifas.ufl.edu/SS420
http://www.ceplacer.ucdavis.edu/files/56529.pdf

This next link has excellent information on caring for citrus. While this file is about growing citrus in Contra Costa County, it has very good information on caring for citrus that apply regardless of where you live. I also like all the references included at the end. It says thick rind may be due to excess vigor, but what it doesn't say is what causes that vigor. Because the thick rind is determined since bloom, there may not be a quick fix if that is the problem. It could be that applying all the fertilizer at once rather than applying smaller doses several times a year triggers vigorous growth. It is also possible the roots get damaged by the strength of that single dose and the tree is responding later with fast growth to get to the flowering stage. However, the article also says only a few citrus can be grown well in that county which it lists. Other citrus respond with a thick rind. This sounds like an environmental problem which can't be solved by amending the soil.
http://www.ucce.ucdavis.edu/files/filelibrary/434/32989.pdf

One thing I just found out in reading this next link is that the way symptoms are expressed depends on the region where the fruit is grown. It accounts in part why different citrus growing states tend to concentrate on specific citrus types, such as navel oranges in California, but not in Florida.

http://www.aphis.usda.gov/plant_health/plant_pest.../citrus.../hlb.pdf

As you can see from my wanderings from one possibility to another, there may be different reasons why the rinds are thick. If environmental, you may have to live it or replace the variety with one that will ripen well in your area. If it is nutrient related, I would have the soil and its pH tested first before applying anything. As you stated you have CLAY CLAY CLAY soil. Nutrients travel more slowly so care should be taken when applying them because if you make a mistake, it takes forever to leach the stuff out. Take advantage of your local Extension Cooperative Service.
http://cealameda.ucdavis.edu/
Through them you have access to all sorts of great citrus information thanks to the extensive citrus growing industry. I understand the problems you have with clay. I grew up in Fremont and spent most of my married life in San Jose before my DH decided he needed a ranch in the wilds of Texas. Now I live outside the citrus growing belt. The only citrus recommended for growing in ground here are kumquats and satsumas. I am forced to grow all other citrus trees in pots. Growing citrus here would be a heck of a lot easier if we didn't have millions of grasshoppers. They start by eating the leaves and eventually girdle twigs and branches.

The variety makes a big difference, you all may be over thinking this. As far as sweetness it may be a matter of you picking them to early. There is no rush to pick citrus they can be left on the trees for months and many get sweeter with time.

I did mention the possibility of having varieties that don't do well in his climate in my first post, but I believe GP is interested in working with what he has. Four Winds Growers lies about 20 miles south of him. I suggested he contact them.

You're dead on with that advice. 20 miles away they should exactly what's going on.