Arielle, Up north, zinnia, snapdragon, forget-me-nots and four o'clocks would die in full shade as you describe it. Your climate is a whole 'nuther world. For maximum color in your garden, I'd recommend talking to local people to find out what thrives in your area. Talk to neighbors with nice gardens and staff at the better nurseries. Find the website for your local agricultural/horticultural extension - it will be associated with a university. Many have searchable online databases and some offer classes on gardening, composting, etc, either free or for a small fee. I also recommend you do some more research before you replace all your soil. That's a big project, not fun, and only necessary where the soil is contaminated with toxic chemicals. If you just have ordinary but uninspiring dirt, sand, clay, etc., you can improve it by adding compost and other goodies. Another option would be to add soil on top of what you have to make a raised garden. And if you get the right plants you may be able to grow them in the soil you have now. Four o'clocks - if you can get them to bloom you'll have them forever. I deadhead mine daily and still miss seeds. One source to get you started: Annie's Annuals is a CA nursery with an online catalog and a great website. There's a lot of information there and it's well organized. Check the "Totally useful plant lists" - there's one for dry shade. (Is your shade wet or dry?) For the rest of us, they do ship plants and they do have plants hardy to at least zone 5. I haven't bought anything *yet.* Here is a link that might be useful: Annie's Annuals

Sometimes 4 o'clock tubers will even overwinter outside in zone 5. I seeded a 1/2 packet of mixed colors near my house wall awhile back. Used the other 1/2 of the packet the following season in another spot also near the house. I have had 4 plants return each year for the past 3 years, two in each spot, 3 of which are yellow. All are very close to the house wall and grow much taller & bigger than the original seeded ones. There have been reports on the forums about others who have had them overwinter in cold zones. So if you have any in a sheltered area right next to a wall you might also try leaving a couple & see if they return.

Four O'Clocks do indeed reseed like crazy! I have mine planted in a sunny border bed along with other self seeders. In the bed I have Four O'Clocks, Cosmos, Tall Verbena, Cleome Spider Flower, Hardy Ageratum and Zinnias. After the first good killing frost I just yank all the plants up and shake them into the planting bed. I also usually have to yank up many weeds at this time too. I then turn the soil over lightly and rake smooth. The following spring I have hundreds and hundreds of plants coming up. So many that I need to thin them out.

Four O'Clocks, Mirabilis jalapa, are annuals in our zone; the seeds should be planted after the last danger of frost in your area. From what I have read, it does help with the germination of the seeds if you soak the seeds overnight or nick the seed casing. Now there is a native Four O'clock, Mirabilis multiflora, also known as Colorado Four O'clock, that IS a perennial (once it is well rooted) in Zone 5 (and into Zone 4,) and I highly recommend it. It dies back to the ground but comes back up in late spring once the soil is warm enough. I bought it as a plant at least 20 years ago; the next spring I saw no sign of it so ended up digging up the area to plant something else. The next year, the plant suddenly reappeared in my "upper garden" where I had dumped some soil from the bed where it used to be - either I dug up some seeds from the plant or the tuber itself and transplanted it. Anyway, it has been flourishing ever since. (No sign of it yet this spring, but I remain hopeful and have the area staked off so I don't disturb the soil.) Note that it grows naturally in dry rocky/sandy soils but somehow does quite well here in my lovely clay soil. http://www.wildflower.org/plants/result.php?id_plant=MIMU Holly