We have a VERY full perennial garden in a southfacing position. I want to add nutrients to the soil this spring to keep my plants healthy, without digging into the garden (I am afraid I will disturb the perennials roots). What can I add, how do I add it, when do I add (I live in Toronto)?
This is an excellent question, and one that many gardeners are sure to be interested in. The very description of a ‘perennial garden’ implies that plants will continue to thrive, and produce, year after year. Yet the powerhouse source of nutrients required for the roots to feed on is often overlooked, or just not considered.
As you point out, actually digging into the soil surrounding the roots, tubers, bulbs, rhizomes or corms may not be well advised. In fact, the more desirable means of amending soil in perennial beds is often the application of organic matter, on top of the existing soil surface. The optimum time to do this is in the fall, when deciduous trees and shrubs are dropping their leaves, and gardeners can opportunistically mulch these, like liquid gold, around their perennial garden beds. By spring, this leaf matter will have broken down, incorporating into the soil’s composition. Likewise, when the ground is free of frost, you can also spread organic compost throughout your garden, choosing from a variety of bagged compost varieties available at nurseries, or your own garden compost. Your garden faces south, and will receive plenty of sunlight and heat, so this organic matter will also help maintain moisture for the root systems below the soil surface.
You mention that your garden is “very’ full, so perhaps take this spring opportunity to remove dead, damaged, or diseased organic matter, and unwanted plants (weeds) from the bed, and consider separating stands of tulips, peonies, iris, lilies, whatever you may have, to allow a lesser number of plants to enjoy a greater amount of nutrients.
Worth noting, you ask about ‘adding nutrients’, and not about ‘fertilizing’, but there are many options for applying soluble liquid, granular or powder fertilizers, including bone or blood meal. There are specialized, phosphorous-rich, fertilizer blends for bulbs. Follow the manufacturer’s application notes carefully: for example, an inadvertently high application of nitrogen can promote perennials to develop more leaf growth, resulting in leggy, hence weaker, stems and branches, needed to support weighty blossoms.
You might want to make a list of the plants in your perennial garden, or take a picture of last season’s growth, and visit your local nursery to research specific nutrient needs, and apply accordingly.
For your bulbs, as an example, here is an informative article: fertilizing bulbs
Enjoy your springtime project!