There's more to planting perennials than digging a hole. It's important to get them off to a good start, if not for the sake of the plant, then for the health of your budget.
Well-planted perennials form masses of roots that help them absorb nutrients efficiently, combat disease and better withstand extremes of temperature, while poorly planted ones develop inadequate root systems. So here's how to put them in the ground properly.
The best time to plant is on a cloudy day. Coping with being transplanted as well as the drying rays of the sun can stress plants before they hit the ground. Start by watering the potted perennial thoroughly until the growing mix is evenly moist. Then, dig a hole that's as deep as the potted plant and twice as wide, to make it easier for the roots to spread outward. Then, fill the hole with water and let it drain.
To remove the plant from the pot, squeeze the sides to break or loosen the bond between soil and pot. Slide the fingers of one hand around the crown – the area just above the roots – to secure the plant. Then, tip the pot upside-down with your other hand, gently coaxing the rootball from the container. Before placing the plant into the hole, carefully tease out the roots at the bottom. For hostas and other perennials with large root masses, you may need to slash through the bottom of the rootball with a garden knife, such as the Ho-Mi Korean hand tool.
Most perennials prefer to be planted so their bases are level with the surface of the ground. A few, such as hostas, prefer to be planted more deeply, and ornamental grasses and other perennials that require good drainage should be planted slightly above ground level. (Find out your plant's preference by consulting a plant encyclopedia or knowledgeable staff at the nursery.) Adjust the level by adding or removing soil from the bottom of the hole.
Once the plant is settled into the ground, fill in the hole with the excavated soil, gently tamping it down with your hands to remove air bubbles. Water thoroughly and spread mulch on the soil surface, keeping it away from the crown of the plant, to help conserve moisture and keep weeds at bay.