Hello OP, do you want to specialise in b2b gardening? i.e. offering services to businesses? or do you want to do household gardening?
I ask as they will look for different things.
A business will look for reliability, liability insurance, H&S certificates and a quick and discreet service. You should be able to maintain their green areas, clear up after yourself, and do all of these when workers (or guests) are not around. Ideally, also look after indoor planters.
For b2b, focus your advertising on those with stand-alone gardens (hotels, wedding venues, small business estates.
Consumers will mostly be driven by price & the fact that you are local (according to Google, over 70% of searches are for a service within 5 miles of the home). Run small online directory ads if you can, newspapers can also be good, and even better are those local magazine-cum-directories that tend to be town-specific publications.
Voucher sites are also good for consumer marketing; perhaps a free lawn feed with every cut, or 'recommend a friend and get a free lawn cut' types. Also good is leaflet dropping.
Avoid SEO or PPC for a while, you don't need it and it eats budget like nothing else. You do need a small website nowadays, a 1 pager is fine, with pictures of your work.
hope that helps,