Where and how are you growing your zinnias? Were they started indoors and transplanted outdoors? If so, how big were they when transplanted and how long have they been in the ground? Are they growing in full sun? How has your weather/rain been recently. What varieties are you growing? All of these details could have some bearing on why your plants fell over. Is it possible for you to plant other, supportive plants among the zinnias, like sunflowers or tithonia?

I don't think planting your zinnias more deeply will help. I think your stems will rot and you'd lose the plants altogether. I hope things improve for you. Is it too late to stake them now? Or could you pinch them back to allow for more branching? Good luck.

Martha

Martha is so right...the issue here is probably cultural. I don't believe that this is a common problem with zinnia. To add to Martha's list, I wonder about over fertilization and planting too closely. Insufficient light was the first thing to pop into my mind, though.

I grow all of my own plants from seed, starting them several weeks early inside. It's imperative that both the light and temperature be balanced (high light/low temps) to insure sturdy, stocky plants for transplanting into the garden.

i have red cap zinnias and purple prince zinnias

Yes they were started indoors but were moved outside fairly quickly and remained in 5 inch deep pots until the pots were filled with roots. the plants were from 6 to 8 inches high when planted into the ground.

some are 2 feet high and blooming like crazy, spaced about 18 inches apart. definitely not overfertilized

a lot of them are staked, but a good portion of them the main stem is laying on the ground with the rest of the growth upright like it was on its knees

happened last year with the same zinnias...oh well

Mine have done the same thing!! They look happy and I don’t know what happened!

Birds chirp. Soldiers salute. Cheerleaders wave pompoms.

It's what they do.

In the past I’ve grown zinnias from seed out in a veggie garden that had no irrigation. They thrived, grew tall & straight and only had to worry about weeds. I’d cut all the blossoms on Saturday and the next Saturday I’d be cutting armloads again. I no longer am able to have that veggie garden so this year I planted a row of zinnias along the side of a shed. They get full sun and irrigation run off from a raised bed. They are flopping all over the place. Never seen anything like it. I guess they must thrive on neglect and dry conditions. I just don’t know.