A difference in climate will have no bearing on whether a plant is an annual or a perennial - that is determined by their life cycle, an annual living through only a single season and a perennial living longer than two seasons. What are often sold as "annuals" in colder climates are truly tender perennials unable to live through a cold winter (generally anything less than a zone 9). For ease of marketing, they are labeled as annuals so consumers will not expect them to be longlived additions to their gardens.

In my experience in gardening in climates such as yours, even some common perennials are not very longlived, as they need a dormancy period of cold weather to renew themselves. Lacking this, they seem to decline in a couple of seasons.

It's difficult to give you a good answer on your second question without knowing the plants in question. Some would definitely benefit from a shearing back after the blooming season, others may not appreciate it. Watering may certainly be an issue, but I've had good luck with cutting back most perennials which become leggy and with dried skirts. It tends to keep them more compact and floriferous.

I would recommend going to one of your favorite nurseries in your area there in Spain. Talk to one of the staff members and ask them for suggestions on how to care for the plants in your area. If you don't know the names of the plants that you have, snip off a few leaves and bring the samples with you (of course, put them in a plastic bag first, just in case your plants have some sort of pest...you don't want to introduce it to the nursery plants).

You could also talk to friends and neighbors who have nice looking gardens. Ask them what their secrets of success are.

I'm certainly not a seasoned gardener, but one thing's for sure. There is not a hard and fast rule of "trim everything back before winter." It really varies a lot based on:

1. the climate (or microclimate) in your area
2. the specific needs of each plant
3. whether you want to trim the plant for a desired shape or appearance.

Have you tried asking your question on the Espana Forum on Gardenweb Europe? They would probably be able to help you.

Based on your description, it seems you have classic Mediterranean weather--hot dry summers with mild wet winters. We have similar weather in Southern California. Many plants listed as annuals are perennials here. However, it doesn't mean that all plants can survive the winter here.

You should identify your plants before doing anything else. Once you know what you have, you should consult with a local nursery and ask them for help.

Loads of useful information from you all.
Gardengal, I had never thought of the dormancy period being neccessary - that makes a lot of sense and also explains some of my failures (plants that had been doing fine for 2 years and then suddenly gave up the ghost). Also, I loved your description of "leggy with dried skirts"; fits lots of my plants to a T. I will try cutting them back and see what happens. Definitely works with the osteospermum, has worked with the blue sage but I think that´s now on its last (leggy) legs, hasn´t worked with the felicia amelloides, hoping it will work on the chrysanthemum frutescens....
There IS a Spain forum, it´s just that Spain has so many different climates and ours is a bit unusual (lowest rainfall, most sun) - so much of the info on there is a bit redundant for those of us in this corner of the country. We are right next to Europe´s only mainland desert. Is that still a S. Cal climate, loneranger? Maybe we have less winter rainfall than you do? I will research this.
Thanks to all of you for your information and time
Best wishes
Almeria

Almeria,

Normally, we average about 15 in/38 cm of rain every year. In the summer, it can reach 105F/39C. In the winter, it can drop to 35F/2C at night, but it warms up to about 60F/15C in the daytime. The Los Angeles area is actually a semi-desert.

And like the movies show, we get a lot of sunshine year-round. That's probably about as close to reality as movies and TV shows get. :-)

Thanks Loneranger!
That sounds really similar to here - apart from the TV shows and movies bit (although back in the 60s and 70s, most of those "spaghetti westerns" were made about 20 miles away from here! Funny to think of ol´ Clint riding about the place....)
Best wishes
Almeria

Almeria,

You might also be close to a south TX climate. We get freezes in N. Tx but the south areas are very moderate in winters but VERY hot in the summer. Maybe too hot for you but I'm not sure, I'm in the north part. Tx is a huge state and parts are definately dessert. You might check that forum out also, we are always trying to find plants that handle our heat.

Almeria, as the other posters have said the best forums for you are the ones in the Western United States (Southern California, Southern Texas, New Mexico). In the U.S., zone 10 is a minimum average temperature of 30 - 40 degrees Fareneheit. 32 degrees is zero celsius, but beyond that I can't convert easily! (: The Gulf South states that border the Gulf of Mexico (Louisiana, Mississippi, Alabama and Florida) except Texas (which has desert like climates in parts) are too wet for you in the hot months and too dry in the cool months. I live in southern Louisiana in zone 9, it rains all summer long during the warm months due to the moisture from the Gulf of Mexico, and our autumn, winter and spring are dry.