You are probably not doing too much wrong; but Meyers are quite sensitive to significant light changes. When you dramatically change the light conditions, your tree will drop many/most/all its leaves to replace them later with new leaves better suited to the new light. Have faith and patience and it should be okay.

when tree is stressed ( especially by moving to new location, repotting, etc) it often will go into emergency mode. it will drop its fruit and leaves to conserve energy and save itself. the fruit is an energy sink, so it goes to bottom of the list. as for leaves, if the ones that are dropping are generally the bigger, older leaves then thats a somewhat good sign. younger leaves are more efficient than older leaves, and so the old ones are lower on the list of crucial parts to get the plants energy. they drop and little ones will replace them. keep your eye out for new leaf growth, as that signals the plant is fighting its way out of emergency mode and actively establishing itself. also do not pluck leaves from the lower stem of the tree, commonly called "suckers" on a grafted tree. the lowest leaves on a tree send energy to the roots, letting them grow and develop. wait until your tree is unquestionably growing and developing before you consider pulling off suckers.
as for overall care, see if your city has a water quality report. one of the best things i ever did was start adjusting my water's pH with white vinegar (water was 8.5pH on average). watering with a pH somewhere around 6 is way more beneficial than worrying about soil pH. it keeps your nutrients available to the plant. if you invest $10 for a pH test kit and some vinegar or ph adjustment checmicals you'll solve many problems container plants have with nutrient deficiencies. most bang for the buck in my opinion.

good luck

Barbara, even though you live in Arizona, your tree will need a better porous mix to allow the roots to breathe and the residue salts from fertilizer to run freely out of the pot..

Yes, older leaves usually shed first until a tree readjusts to it's new condition, so no worries..

MIke

Thanks to all of you for the encouragement. According to the city's water report, in 2012 the ph of our water was between 7 and 8, so I guess that's high. With our ongoing drought, it might be higher now. But how can I determine how much vinegar to use?
Mike: if my tree needs a lighter, more porous soil mix, does that mean I need to re-pot it? And if so, should I wait until it is beyond its present transition stage and, say, putting out new leaves, before I do that?
I have loved Meyer lemons since I was a little girl (when the earth was still cooling) and had one (the unimproved kind!) in my backyard. I would so dearly love to have this one thrive.
It's so nice to have such support from you all!

That's the same pH as my water, Barbara, and I never adjust my pH for my citrus - container or in-ground. I agree with Mike - even though you're in a very hot and dry climate, the bottom of that pot could end up retaining a lot more water than you think. Here's what I do for my container citrus here in sunny S. California: I mix 3-4 parts Cactus Mix (I like EB Stone's mixes) or, I've even used Miracle Grow Garden Soil for Vegetables, and 1 part small bark chips (I use a reptile bark mix I buy at Petsmart) and 1 part vermiculite. Sort of a modified version of Gritty mix recipe, since I, too, live in a relatively dry climate, especially in the summer, when we get zero rain (as opposed to AZ, which can get monsoon rains which rarely reach us here on the San Diego county coast). I fertilize with Osmocote Plus, an excellent time-release fertilizer with a very good NPK ratio for citrus, plus I'll use Dyna Gro's Foliage Pro about once a month. My citrus thrive with this combination. Your location on the north side of the house to get shade during the most searing time is excellent, and John's advice of patience with a Meyer, as they are sensitive to light changes is exactly what I have found with my Meyer. That, and the fact that they seem to need more fertilizing than any of my other citrus cultivars (right behind the Meyer is any other lemon and my limes). I think it's due to the prolific fruiting abilities of these cultivars. Your tree looks fine, just watch the bottom of the pot to make sure the roots aren't sitting in a puddle of water (use a stick, and shove it down to the bottom of the pot and check to see how wet the stick is). If the pot is consistently wet, then re-pot with a more porous mix as I've suggested. Patience and a close eye will tell you if your Meyer is adjusting and thriving.

Patty S.

IMHO... never use vermiculite; it is an absorbent mineral additive; instead use perlite.
Aside from that a Meyer needs a special food and a lot of it; the book wisdom for citrus is an NPK ratio of 5-1-3 Meyers need 3-1-2 with 2 % CA and MG and 1% FE and ZN. Meyers do best in soil with pH of 5-6.5 pH; they can tolerate pH up to 7; beyond that there are special things you have to do to be successful.