Color, not all of your perinneals bloom all growing season, since the annuals grow so quickly, they are alot of fun to grow. Some perinneals dont bloom til second or third season. Annuals are great for filling bare spots. Lots of winged friends like them too! If my plants I have now die back due to this freeze, I"ll still have my annuals. Easy ones are zinnas, cosmos, marigolds, so many varieties to choose from.
Price. Annuals are usually cheaper and can go a long way in filling in a new bed (with almost instant blooms like crash said above). Or, for the price, you can have one of each, like Al said. LOL!
Also, a lot of annuals will reseed on their own, so that is something to consider. I planted Petunias 5 years ago in a huge pot and have never had to replant since. The originals were hybrids, so I never know for sure what I'll get from year to year and I love the surprise!
1. Bloom all summer...perennials have a more limited season.
2. It takes a couple of seasons for perennials to bloom...and many are not at their biggest and fullest for 4 or 5 years
3. Cheaper if you're just starting out...you can get several big flats of annuals for what just a few nice perennial plants cost
4.Will keep butterflies and hummingbirds in your yard for a long period of time...perennial plants will sometimes be great nectar plants, but when the blooms are gone...so are they.
On the up side of Perennials...you can establish wonderful beds of long lived plants that require very little maintainence.
I dearly love both...and feel that each has a place in my garden. Perennials make up my 'bones' (the basic shape and contours of my beds) Annuals add a splash of color and change up the landscape from year to year.
Sort of like your house...you have a nice dining room suite of antique cherry..(maybe your Grandma's)...and you don't throw it out when you want to remodel ...but if you want to make your dining room look fresh and updated, you change the wall color, the drapes, pictures on the walls, and the tablecloth. Maybe even a different pattern for your dishes...but, Grandma's dining room suite remains. That's sort of how I look at my perennials and annuals...
Ok, now I get it! I'm so glad I asked because I was finding myself only looking at perinneals when shopping because I'm a bit frugal and didn't understand why I'd want to spend money (and the time it takes to plant) on annuals knowing they wouldn't come back next year. But now I have a different perspective and will give them a try. Thanks everyone for your replies!