50 Basic Perennial Garden PlantinG & Maintenance
Transplanting
When transplanting perennials, it is best to water the plant the night before you
plan to move it. Dig the hole as near to the size as you think you’ll need, making
any necessary adjustments immediately before planting. Take as much soil with
the plant as possible. Add organic matter to the new hole and backfill. Firm the
backfill in as you go, water when the root ball is covered, and then continue to fill
the hole. Transplanting ideally should be done in early spring as new growth is
emerging or in early to mid-September. It’s best done after flowering, and plants
should be cut back by half to two-thirds before transplanting if in a mature state.
Transplanting can be done even when the plants are in flower, but they must be
handled with extra care. Genera such as Astilbe, Coreopsis, Geum, and Phlox can
handle transplanting while in flower. Larger plants as well as certain genera such
as Dictamnus (which is difficult to move even under ideal conditions) and Papaver
will have more trouble at such nonconventional times. Transplanting on a
cloudy or overcast day with low wind is best. Plants may need to be shaded for a
couple of days if transplanting is done during a period of high temperatures or if
the plant is in a mature state. See the Encyclopedia of Perennials for transplant-
ing requirements or limitations for particular plants.MULCHING
We have become a society of overmulchers, feeling compelled to go out every
spring and mulch, regardless of whether it’s needed. Mulching makes the garden
look neat and tidy, but we are suffocating our plants by piling the mulch up—
especially on shallow-rooted woody plants like azaleas and rhododendrons—as
well as potentially contributing to the rotting of our perennials.
A variety of different materials are available that can be used for mulching,
but a light, fine-textured material is most suitable for perennials. I use a pine
bark that is actually sold as a soil conditioner. It is similar to but slightly smaller
than pine bark mini-chips and is dark, like the soil itself. Pine bark is easy to
apply and to work with later for any additional planting. It can be worked directly
into the soil. If I am applying a topdressing of compost, I do not use additional
bark or other mulching products.
In the spring it is best to wait until the soil warms before mulching. No more
than 2 in. of mulch should be applied, and it is most critical to keep the mulch
away from the crowns of the perennials (where the stem meets the roots, usually
found at soil level), as mulching over the crown will cause rot. I like to mulch the
beds with 2 in. of material after planting, when the perennials are establishing.
After that I use it with discretion, keeping the doses between 1 and 2 in., a suffi-
cient amount to help control weeds, reduce moisture evaporation and tempera-
ture fluctuations, and protect against erosion and soil compaction. For perennials,
I find that reducing winter temperature fluctuations in the soil is a primary
benefit of mulching. Not only is frost heaving harmful to the plants, but research
indicates that fluctuating temperatures also can cause certain physiological
changes in herbaceous species that can weaken the plants and lead to death.
I rarely apply extra mulch for the winter. I only use perennials that can take
our winters without this extra maintenance chore. Besides, I enjoy my perennial
garden in the winter and don’t like the idea of mounds of mulch or evergreens
lying about. The exception would be for perennials transplanted or divided in
autumn, which need 3 to 4 in. of mulch applied over their crowns after the
ground has frozen. If you choose to grow marginally hardy perennials you will
also need to follow this practice. In addition, certain subshrubs (plants that have
a woody base but also have herbaceous shoots aboveground that die back
annually) will burn if there is not persistent snow cover. They can be protected