For you, Florence...
Ants in your garden could be feeding on honeydew excreted by aphids, mealybugs, scales and other insects. Ants actually farm the insects and protect them from natural predators. While it is possible to control ants, it is also recommended to control the other insects that are attracting the ants...
To prevent ants from crawling up plants you can apply a ring of sticky barrier substance low down on the stem. A commercially available one is called tanglefoot, however I am sure there will be a number of home remedies that work just as well.
My friend Google has given me the following tips to try:
1. Bay leaves - I found a fair few places that recommended this so definitely try it
2. A ring of electrical or gaffa tape, sticky side out around the stem/ trunk
3. Ideas for sticky barriers - vaseline, used cooking oil, honey, eucalyptus oil
4. Pipecleaner soaked with peppermint oil
4. Boiling water poured into the nest
5. Spray 50/50 water vinegar mix onto things to deter them - not sure how this will affect plants
6. Sprinkle salt, talcum powder, flour, cayenne pepper, cream of tartar, borax, powdered sulphur (sounds like you can use almost anything lol but these were for inside house or around foundations rather than the garden)