How to select the best landscape design contractor
Always select a company that is reputable and a company that appears that it will remain in business. The cheapest contractor will usually not stand behind their work because in most circumstances this cheapest contractor will sub contract out the work and the sub they used will not be their to fix your issues should they arrive or an additional fee will be presented to fix an issue that should have been covered in the original contract.
Select a company where the owner will be on-sight throughout the contract. This will eliminate any major price change issues and changes to the original project will be resolved much faster and in a fair manner. In many cases the sales people will only show up during the sale phase. Because of this many items get lost and never get completed because of what was promised and not correctly documented in the construction plans. Your project will be completed faster and more professionally if the owner is involved throughout the project.
Clarify the warranties, get them in writing, select a landscape designer that listens to your vision and needs. Dealing with a company that designs and builds is usually a safer way to achieve your goal.