I think they are treated as annuals for the best display. I've had alyssum and petunias flower in the second year by cutting them back but the flowers are not as good. That's why they are normally replaced every year.

Many seed packets have planting instructions on the back with a map showing the climate areas and planting times. Alyssum usually self seeds and can be planted any time. If you plant now they would all be ready for the garden before winter. The general rule is that the depth of planting depends on the size of the seed and tiny seeds just go on the surface and get tamped down.

Alysum is both an annual and a perennial: the perennial form has yellow flowers, not unlike the annual form and is quiet a nice plant. The annuals come in white and various shades of lilac to purple. Impatients are treated as perennial and apart from the New Guinea or tropical forms are quite invasive, they have exploding seed capsules that scatter the seeds everywhere and I think every one of them germinates. They're easy to pull out though. Petunias, well, they are mostly treated as annuals but nurseries in recent years have been stocking perennial forms, but their flowers are smaller and not as eye-catching. On the annual forms, you can cut them back after the first spring flowering and they should shoot again but I pull them up when they start to look a bit ratty. The perennials are ok but they seem to need heaps of water. Unless specified on the packet, I'd say the seeds you have are annuals. Depending on where you garden I'd plant them in spring. All those you've mentioned are popular spring /summer annuals.

Hi there,
I know it is a long time since this thread started, but just reading thought I would pass on my comments.
I have found that Alysum does get old and tired after a few months, but I just cut off the dead bits..because it seems to self seed, then discard the old plant when the new comes up. It can go on for ages this way. Plus I have noticed that it looks dead, then a few weeks later starts flowering again. Great anywhere in the garden as a ground cover saving on mulch! With Impatiens.....I have had lots of success just breaking bits of and sticking them in the ground, and a new plant developes. For a rather large pot, I just popped in heaps of cuttings, so the whole pot is now really full of doubles and it looks lovely.
Jenny