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Quick Digs: Putting Salvias to Bed with Winter Mulch

Oct 14, 2013

Quick Digs: Putting Salvias to Bed with Winter Mulch

During spring, a heavy coat of fall leaves or wood mulch isn't a good idea for sages (Salvia spp.), because it can cause fungal problems that attack crown and roots. But in winter, organic mulches are ideal for blanketing the foliage and root area of sages.

Mulch is particularly useful in protecting protect plant roots against injury from freeze-and-thaw cycles, especially for new fall plantings.

Let's say you live in USDA Cold Hardiness Zone 6 and have recently planted some Zone 5 or 6 Autumn Sage (Salvia greggii spp.) that are now about 18 inches tall and wide. However, you are worried that the plant roots aren't established enough to avoid heaving out of the ground when it freezes.

When ground thaws, heaved roots don't always sink back into the ground with the shrinking soil. Often, they are exposed to dry, cold air as well as more freeze-thaw cycles. One way to minimize this problem is to wrap mulch blankets around each plant.

Building a Mulch Tower
Tomato cages are good structures for holding leaf mulch in place when plants are small. Here's how to do it:

  • Determine how much taller a tomato cage is than the plant it will surround.
  • Snip off portions of the cage's prongs to decrease height -- leaving it somewhat taller than the plant -- and to increase the diameter of the prongs so they won't harm roots too much.
  • Insert the cage in the ground around the plant and gently stuff it with dry leaves.
  • Cover the structure with a sturdy, plastic garbage bag and snug it up against the cage by knotting it at the cage's base. This keeps the mulch dry.
  • Hold the opening of the bag in place with rocks.
  • Poke some small holes in the sides of the bag for air circulation and to minimize condensation buildup that can cause rot problems.
  • Remove the mulch in spring when threat of frost has passed.

To protect a new planting that is larger -- or even an older sage that is cold-appropriate for your zone and has a well-established root system -- apply a thick layer of leaf mulch around the plant's base.

But what do you do if you have a flowerbed filled with beautiful sages that are perennial to warmer zones? Furthermore, what if you don't want to dig them up each year to overwinter indoors?

Here is an innovative idea from a gardener who tired of losing favorite plants, such as Mexican Sage (Salvia Darcyi) and Cedar Sage (Salvia roemeriana) to harsh winter weather.

Creating a Mulch Comforter
We pay close attention to horticultural professionals, but also encounter excellent ideas on gardening social-media sites. For example, the Hummingbird Forum is a great place to chat with experienced Salvia gardeners, such as a Minnesotan who manages to keep Zone 7 plants alive through Zone 4 winters.

Normally, we don't recommend pruning sage in autumn, but this method requires it. It also requires a raised-bed planter amended with sand for excellent drainage, because damp roots are dangerous for sages in freezing weather.

Here is how the Minnesota gardener puts his Salvias and companion plants to bed for the winter:

  • Wait until hard frost kills foliage and then cut back your plants to a few inches above ground.
  • Fill enough sturdy garbage bags with dry leaves to completely cover the flowerbed two bags deep.
  • Cover the garbage-bag layer with a tarp weighted down at the edges with heavy objects.
  • Leave snow on the tarp, because it's a natural insulator.
  • Uncover the flowerbed in spring after threat of frost has passed and check for new growth.
  • Don't expect all the plants to survive; celebrate the ones that do.

Quick Digs and Questions
This is the second article in our current Quick Digs series on preparation for winter in the Salvia garden. Each Quick Digs series selects a central issue about gardening and provides a series of brief articles suggesting ways to deal with the issue.

Another way to deal with questions about winter mulching is to contact us. We can't offer any works-every-time solutions for overwintering, but we are glad to share ideas.

Updated October 26, 2015


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Plants mentioned in this article