Written contracts usually protect the homeowner or client and also the landscape company from any misunderstandings. They provide for the scope of work, the total cost, time period for completion and any implied warranties on trees, plants, sod, etc.
This is a good time to revise the contract and identify if the contracting company has all rightful insurances and will be reliable of any damages towards property and any injury of employees. The more detailed the contract, the better.