First, what Is soil? Soil is minerals, humus, water, and air. In real estate, it’s location, location, location and in gardening, it’s drainage, drainage, drainage. Air space plays a big part in this drainage. Water moves in the soil in two ways: it drains down until it enters the water table or it rises back to the surface and evaporates.
Mulch helps prevent this evaporation and keeps the moisture in the soil longer. Mulch also smothers weeds, adds a bit of insulation value in the winter plus it eventually breaks down and becomes humus, which feeds the plants. According to the University Of Georgia, you do not need to amend the soil for individual planting holes. However, amending the area or planting bed is beneficial. Clay soil is good. Repeat after me “Clay soil is good.” It is full of minerals and it holds water. The problem is, it holds too much water therefore it needs amending. Never use play sand as an amendment although that is what garden shops will try to sell you. Play sand is too fine and mixed with clay will make bricks. Instead, use builders or construction grade sand.
When siteing a plant, begin by digging a wide hole and removing grass and grass roots. If the area is in sod, you may want to make your life easier by starting out with a spraying of Roundup. Add to this site any number of products: Nature’s Helper, pine bark mini nuggets, sphagnum peat are all good organic amendments, some may have a knee-jerk reaction to the mention of peat and the environment. Peat is being managed to where it is regenerated plus think about how no new gas and oil is being created but no one is quitting using those products. Add perlite or vermiculite and the aforementioned sand or sharp gravel to improve drainage. Do not add fertilizer at this time unless it is organic or timed-release such as alfalfa meal (rabbit food sold at feed and seed stores) or Osmocote. Add a bit of lime (even if you are planting acid-tolerant plants like blueberries, azaleas or camellias because ALL plants need calcium). Presoak some water polymers and add them. Mix the ingredients well in the planting hole. You should have a raised mound, not like a fire ant bed but more like a pitchers mound. Be sure you add some clay back to this mix. Now you have an amended planting site that has balanced nutrients and excellent drainage. Anything you plant should thrive in this location. I once gave a talk on amending the soil to a group of non-gardeners and when I finished spelling out all the amendments I used like greensand and magnesium and such and all the steps I went through which sometimes amounted to half a day planting a plant or two, they absolutely didn’t believe me.
The secret to good gardening lies in the soil not the plants. That is the key to it all.