This is difficult with Sweet Rocket as it is a biennial. It is, however, very easy from seed and if allowed to seed around, you will soon have many plants to conjure with.

I find that left alone they do go on for at least 4 years, but they only flower in their second year. they are not suitable for splitting in my experience. but they do seed freely and you may get a different colour coming up.

i find that they dont split readily. however I have a couple that are 4 yrs old now and a good size. they flower in their second year and are short lived. they do self seed freely and I have white , pale pink and lilac now. they produce hundreds of seed and thankfully are easy to weed out.

Thank you

And I thought rocket was a vegetable ! Guess I've a lot to learn.