How do you amend existing soil with compost around individual plants and their root systems?
Last season a landscape contractor planted new perennials in several beds around our home with instructions to remove and set aside mulch this spring, add organic compost around the plants, and replace the mulch. Websites I have consulted recommend working compost into the top 6 inches or so of soil, but this seems like a pre-planting recommendation rather than one for new or established plants. How does one amend existing soil with compost around individual plants and their root systems?
Your contractor is staying on top of the latest research. The scientific opinion on this topic has changed over recent years; we no longer recommend working compost into the soil.
Even shallow tilling will disrupt the soil biology, including the networks of mycorrhizae that attach themselves to the plant root. These organisms serve to "extend" the roots, assisting greatly in nutrient uptake. What's more, incorporating compost into the soil can steal away nutrients (such as nitrogen) from the plant roots as as it decomposes.
Your contractor's methods are sound. Pull the mulch away from the root zones of plants and spread finished compost about 1/2 to 1-inch deep. Then recover the area with mulch (preferably organic). If done on a regular basis once or twice a year, this will normally satisfy the plants' nutritional requirements.