Below I have copied and pasted a similar question and answer I found on the web. Hope it helps.

Q: I planted a few hollyhocks two summers ago. They bloomed and flowered beautifully, but now I have tons of plants showing up. Last year I left them alone, but they never produced flowers. I eventually tore them out. I don't know if I bought biennial or perennial plants. I really love them and want them to reproduce, but with no flowers, the plants look like weeds. I love lilacs and have a few of them in my garden. Are lilacs a type of the plant that if I cut off the flowers they will keep blooming? (e-mail reference)

A: I wouldn't rip out all the hollyhocks. Keep just enough plants to keep your garden from looking weedy. You may have biennial hollyhocks that require another cold period before they will flower. Lilacs will flower every year if you harvest the flowers. The flower buds are set for the following year on the subsequent growth that takes place after they flower. If you prune the plants late in the summer, you will remove the flower buds for the following year.

Sue

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