Crown of Thorns not blooming

I planted a row of them outside the house, they are getting some shade from a row of palms but still plenty of sun, they look very healthy but never bloom...
Sue

Are you sure they are really COT? They should be blooming continually, outdoors in the sun in a mild climate. Do you have a photo?

I've been waiting until someone answered this and now that there is a response, I'll weigh in. I have this plant on my desk in the office and it too rarely blooms. I've had it for about a year and a half. Perhaps it's not getting enough light?

Perhaps. If you can give it daily sun you will probably see it perk up significantly. Indoors right by a window with good exposure should do the trick.

Yeah but I only have north side windows in my office. I just started giving it some fertilizer, we'll see how that goes.

Fertilizer may help but it won't substitute for light. I would caution against using too much fert with an indoor Euphorbia, maybe 1/4 the recommended dose a couple times a year.

Ok, thanks for the tip!

I will take a picture, hopefully someone can give me a tip:)

Here they are....

And here is a close up...

I wonder if the soil is too alkaline for them? It's just a guess but I imagine all that concrete around the soil might make it more alkaline and perhaps the plant doesn't like it?

It looks like the real thing. No idea why it hasn't flowered. Try a bit of fertilizer?

Hmmm quite possible...what would I put in the soil to equalize it?

Well, if it is as I suggested, you would want to do a soil test first. If it is too alkaline, then you might add something like Ironite to the soil once every few weeks. And, really, I'm just guessing at a possibility. It also might be beneficial to look up which type of soil your plant thrives in.

I too have COTs that are so lazy to bloom and I have to feed them with bloom booster to bloom. I think there are cultivars that are prolific bloomers and there are some that are soooo stingy to show their bloom. I collect COTs and really I give each and everyone of them same treatment, soil, sunlight, water, fertilizer plus a lullaby but they do not give me back equal treatment.
There are things though that I have learned about why COTs don't bloom despite all those TLC's that we give to them. First, which is the obvious one is they are not getting enough sun which is at least 6 hours a day. Second, they are getting too much nitrogen so all they do is produce leaves and more leaves (your plants have a lot of healthy green leaves). Third, they also have to go to sleep during the night in order to bloom. Remember that they are cousins of the poinsettia, they need a particular amount of darkness to produce those magnificent blooms. Do you happen to have a street light or a garden light that is on during the night near your COTs? If so then that is one of the reason why your COTs don't bloom.
The nights are becoming longer now so I bet soon your COTs should be blooming like some of mine.
These are merely my own observation plus some info I have gathered over the web regarding this particular topic. I have more than a hundred pots of COTs, Thai hybrids, and recently I encountered a gross problem regarding my collection. I spent hours per day Googling for answers and these are some of the info that I have learned.
Hope it helps!

The 5 different COTs that I have were blooming when I got them and they have been blooming continually ever since. Realistically I would not acquire a plant if it was not in flower, so my experience has obviously been limited. Were the plants blooming when you got them? Have you seen the flower?