Answer: Dames Rocket (Hesperis matronalis) is generally self supporting, between two and three feet tall, and prefers full sun so based on your description I would guess they are stretching for more light. (Other possibilities are a driving rain storm and excessively lush growth due to over fertilization.) Staking might help, but it won't stop them from stretching. Since they have already bloomed, trimming them is not likely to force another flush. Unfortunately they only bloom once a year and are in fact often biennial rather than perennial. You may find that they will self sow to make a self-perpetuating patch, however, if you allow them to set seed.
If these leaned because of the light, your hollihocks will probably lean, too. They will need to be staked to avoid a big mess when they bloom and it rains and they all fall over at once.
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