What city do you live in?

Does it get 100+ degrees in summer where you live? If so, nothing will do too well in full sun (6+ hours or full afternoon sun). The sun is too intense and the pot soil just gets too warm.

Conversely, if you can put your barrels in morning sun/afternoon shade, you can grow almost anything, assuming your soil, nutrients and water needs are taken care of.

Don't give up on your lemon tree. It's hard to keep them looking good outside during winter unless you live in Miami or San Diego. If you think it can hold on for another month, I'd give it a shot of mild liquid fertilizer now. You will still need to address the hot afternoon sun problem though.

Soil is important, but you haven't mentioned how you water or fertilize. I'm not particularly familiar with the lavender grevillea, but the Meyer Lemon should do well in that location. If you're just looking to replace instead of resuscitate, Hummingbird mint, Agastache 'Desert Sunrise' could be a good substitute. It loves the sun and tolerates dry conditions.

To replace the Lemon, (if you're looking for a tree and something edible,) an olive may be a good fit for you. It would require a bit more work, but should be happy with some pruning maintenance. :)

Fuschia , tree type, not vineing kind.

It is frost tolerant, blooms non stop, there are various colors of it.

Thanks all for the tips and suggestions! Attached is a photo of the Meyer Lemon. See how yellow?? (I have one of the grevillea as well, but can't seem to figure out how to attach several photos.)
Oxboy: I'll try the fertilizer. Haven't done much fertilizing so far. For the lemon tree, if I give some fertilizer now, how often and when would you repeat?
MagsterGardener: The Hummingbird Mint sounds fabulous. I'll try that if my current barrel plants don't make it.
Seysonn: What kind of Fuchsia are you suggesting? Australian Fuchsia? Other Fuchsias don't seem very cold tolerant, or drought tolerant.

About Fuchsia, I don't know the variety name but it overwinters here in zone 7. Most are cold hardy down to zone 6.

I got the following from internet:

""drought-resistant California fuchsia (Zauschneria spp.)""

IMHO, that soil looks very peaty and compacted -- nothing like 5-1-1. At least the leaves haven't fallen off.

I would get some Foliage Pro or similar liquid fertilizer and give it a half strength shot, then follow up two weeks later with another dose. See if it greens up a little or looks like it might put out some flower buds. All that excessive yellow could mean too much water.

Oxboy, you're exactly right about the soil!! I had taken the photo before I changed the soil just a couple weeks ago. wasn't able to find pine bark fines, but I mixed the existing soil 1:1 with perlite, since I had read on another forum that somebody had success with that mix for a lemon tree. I also followed your advice about the Foliage Pro. I guess the yellow leaves won't turn green again, but fingers crossed for new growth! Stefanie

I plant lots of annuals in my half-barrels. I can't overwinter much in a barrel here. Except for mint (chocolate), peonies and daylilies. I did have a delphinium that kept coming back, but we've had a brutal winter and I don't expect to see it this year.

I plant seeds: tithonia, yvonne's salvia, cosmos, sunflowers, and zinnia (red spider is my favorite). I've gotten all but the cosmos in a swap.

Have you considered a rose? I'm in zone 6 with very cold winters, but I've had success growing hybrid tea roses in containers that hold 15-20 gallons for the past three years. I have to protect them from temps under 25 by storing in an unheated shed, but you probably could leave them out year round in your zone. I am growing them in the 5-1-1 mix popular in this forum. I chose disease resistant varieties, and they bloomed all summer.

Thanks for all the additional plant ideas! Now I feel like I should buy another couple barrels ;-)
october17: when you plan annuals in half barrels, so you sow them right in there or raise seedlings? Delphinium sounds nice...but I read about those being really hard to raise from seed?