bright, brightly coloured/colored, brilliantly coloured/colored, colourful/colorful
fragrant, scented
delicate
little, small, tiny
big, huge, large
bell-shaped, star-shaped, etc.
exotic, rare
garden, tropical, wild
spring, summer, etc.
seasonal
beautiful, lovely, pretty
What beautiful flowers!

fresh
cut
They sell a few plants, but they mainly sell cut flowers.

dried, pressed
dead, wilted
artificial
plastic, silk
closed, open
The flowers were still tightly closed.

blooming
hibiscus, lotus, etc.

bouquet, bunch

bear, have, produce
It has deep pink scented flowers.
It was the first year that the cactus had produced flowers.

pollinate
The flowers are pollinated by insects.

get, receive

appear
go to seed

bud, head, petal, seed, spike, stalk, stem
bed, border
arrangement, arranger, arranging
I'm learning flower arranging.

display
basket, container, pot (usually flowerpot), vase
garden
festival (BrE), show
market, seller, shop, stall (esp. BrE), stand
power (= hippy culture)

in flower
It was June and the roses were in flower.

a bank of flowers, a carpet of flowers, a mass of flowers
The alleys were adorned with banks of flowers.
The forest floor was a carpet of wild flowers.

covered in flowers
The bush was absolutely covered in flowers.

come into
If the winter weather is mild, plants may come into flower too early.

in full flower
The park will have cherries in full flower this month.

Flower is used with these nouns as the subject:
bulb, shrub