Hi Ezz,
I sprinkled allysum seeds in my garden last year. They must be very easy to germinate because I had a huge success. I did not do anything special; I just tilled the ground. I waited till late April and had flowers in June. I don't think you even have to wait till the last frost, though.
They grew like crazy in both morning and hot afternoon sun and continued their flowering after frost.
I thinned them as they grew, according to the package directions. They spread and made a nice carpet-like edge.
rooty

Allysum likes to germinate in cool soil and the plants can take light frost. It is slow growing and takes a couple of months to get a small plant in bud. If you are planting outside, I'd say in your zone the best time for you to plant is now. They will drop their seeds and come back another year if you watch for them.

I was excited to see that Home Depot had the new Hybrid sweet Alyssum "Snow Princess". It is supposed to be more heat tolerant then the older varieties, which is a big plus in my zone. It is actually a tender perennial to zone 9, and supposidly after being sheared back in fall can be kept inside as a house plant over winter if given adequate sunlight (which I do not have)...I grow the regular sweet Alyssum too and am pleased to see it has returned from self seeding for the last 2 years. One customer at the nursery thought she had a really unique and special kind because hers has come back for many years. I think that rather then some new strain of super hardy alyssum hers has just probably reseeded also.

No you don't have to wait for the last frost. You can plant allysum as soon as you can work the ground. It likes to sprout in cool temperatures and doesn't freeze easily. I live in zone 3 and often have them reseed themselves.

maryl:
I would leave yours in the ground and put a good layer of mulch around them and under the growth to protect the roots--don't cut them back their growth will help protect the roots too

Actually I'll be using the Snow Princess Hybrid as a hanging basket. It's supposed to trail up to 3 feet or so. We will see. The thing I'm most concerned with in my zone is something that can make it through our horrible hot and humid summers. That's more of an accomplishment to me then hardiness. ;-)

I forgot about the heat here in zone 7...I will get them in the ground this next week. I am excited by the possibility they may reseed..

maryl:

I never thought of that. Here we are more concerned with getting things through our cold winters. I couldn't take that kind of weather myself--my ideal temperature runs in the high 70's. I guess it's what you get used to, I'll bet my ideal would feel cool to you.

Alyssum doesn't like the heat either. I hope you are planning on planting it where it's shaded during the heat of the day. I've never planted that variety. My favorite Allysum is Easter Basket and I have ofter used it as a filler in pots