A natural would be to apply with pond installers. Local greenhouses and nurseries would be another place. They have probably filled their seasonal positions by now, but someone may have quit.

Check with the community college system to see if there is a hort. program near you. Now would be the time to start the application process.

Volunteer at a garden. You'll get a feel for the work and make some contacts.

Firstly, know your subject. Go to the library and read as much as you can. Learn about he trees, shrubs and perennials in your area.

Work! Do everything from weeding to planting trees. You'll learn by doing and get to know the market and opportunities in your area. The suggestion above to explore volunteer opportunities is excellent

Please excuse this nitpicking. You spelled experience twice as 'experiance'. just a warning in case you submit a resume and list your work experience under 'Experiance'.

alpiner's suggestion made me think of this...
Do work for people you know. Then you get more references. This has helped my partner and I a lot in our business.