I often hear people who are concerned about how plants will be installed, long before the planning and design stages. This is akin to worrying about the paint color on a house that isn't built yet. Once you've completed your due diligence on removing weeds / unwanted plants, planning and design of the landscape and the sources of the plants, THEN consider an installer.
Planting landscape plants is hard labor, but technically simple. The steps to success are straightforward enough. Here are my views on installing landscape plants, in order...
First- mark the planting site with spray paint, including the edges of the planting hole. Surveyor stakes or colored flags are neat, but can get moved or knocked over in the work process. Using paint + flags is the best idea of all.
Second- make sure the digging crew knows how wide and deep the holes should be. 3 times the diameter of the rootball and slightly deeper than the root ball is my recommendation. This ratio works well for most plants. Use some of the backfill to fill in the hole to match the soil with the level of the rootball. One tactic I use often is to fill the hole 1/2 full of water to check drainage and see how long it takes to drain away. If the water drains in 15 minutes or less, plant the plants. If not, consider a different site.
Third- I like to mix some organic material such as compost or Milorganite into the backfill to get the root system going quickly. There are debates on this, but I've found it effective. Park the plant in the center of the hole, match the rootball level with the surrounding soil level EXACTLY , and add backfill, tamping the backfill with a shovel handle to eliminate air spaces as you go along. Take a lot of care not to scratch or abrade trunks or stems, and tip the plants into a planting hole, don't drop them in .
Fourth- just before you finish backfilling the hole, add water, and let the water drain down. This will really settle the soil around the plant. Finish filling the hole, and make a "doughnut ring" of soil at the edge of the hole to act as a dam to hold water. Without this ring, any water you add will drain off to the side, rather than settle down into the rootzone. You are almost finished, two more steps....
Fifth-any plant taller than about 2 feet needs staking. Heavy bamboo stakes are good for plants under 5 feet, metal electricalpipe is my choice for stakes taller than 5 feet. GENTLY tie the plants to the stake with plant tie tape or rope ( not wire), leaving a little space for the plant to flex.
Last- use 4-6 inches of mulch over the entire digging area, taking care not to mulch against the stems or trunks. Water the plants daily and heavily for 30 days, then monitor the plants for drought stress afterwards. Usually, twice a week watering is sufficient after the initial grow in period. These are simple steps to planting landscape plants. Take care of the plants at these early stages and they'll mature into the plants they can be.