Question
I live in West Texas near Odessa.  I have had four-o-clocks come up (from tubers) in the ground around my patio for the past 15-20 years.  This year they are as tall, about 5 ft., and as bushy as ever but have failed to bloom. Any suggestions?  

Answer
M.Rowe,
Plants don't bloom for a variety of reasons - I'll suggest a few here and you can decide if any of them apply:
1. Too much nitrogen.  Nitrogen stimulates leaf growth at the expense of flowers.  Sources of too much nitrogen include lawn fertilizer, dog pee, and manure.
2. Too much shade - as plants in a landscape mature, sometimes gardens can be in more shade every year.  Make sure your four-o-clocks are still getting the same amount of sun.
3. Change in pH of soil - if the pH is off, a plant might not absorb the nutrients it needs to bloom.
4. Too much or too little water - has the weather been normal?
5. Crowded roots or damaged roots - if the area where they are growing is small or tight, the tubers might be too crowded.

What should you do?  If you can figure out from the above what the problem might be, and if you have control over the situation (can change the shade problem, or the pH for example) that might help.  If you think too much nitrogen is the problem flood the area well with water, and then apply a small amount of super phosphate and water or don't water normally.  (in other words, only flood with water once to wash nitrogen out of the area)

You might also dig one of the tubers up to make sure it looks normal - no rot or signs that it's being eaten.

The other possibility is to cut some of the stalks down by half and some to the ground to sort of shock the plant - some plants flower best if under stress, and if you can't figure out what is wrong, you might try some pruning and see if it gets things going.

The thing about plants is that sometimes we NEVER know what was going on!

all the best,
C.L.