Four Things That Kill Perennial Flowers Over The Winter

And there are a few things you can do to help Mother Nature

Photo by Galina N on Unsplash

The soil is too wet

A soil that holds excessive moisture over the winter will rot plant crowns. A winter that has a great deal of freeze-thaw cycles will create wet soil with a layer of ice over top and this is certain death for many plants.

While I used to keep my mulch over top of all my plants in the winter, I now pull it back from all the crowns at least 8-inches. This space allows the crowns to breathe and lose excessive moisture (as long as there isn’t a layer of ice on the soil). The plants also come up faster in the spring with this clear area around the crowns.

If you have problems with overwintering perennials or if you want to push the gardening zone on perennials, the single most important thing you can do is increase the drainage in the garden or grow those tender perennials in well-drained areas.

It’s too cold out there

Excessive cold will kill tender perennials planted in colder areas.
Butterfly bush is an excellent example. Many garden centers sell it as a hardy perennial but in USDA zone 4, it is marginally hardy.
Buy plants hardy in your zone

Plants in containers on a deck or in a garage

I remember some research from “back in the day” saying plant roots died at 5F or -15C. So if you’re trying to overwinter a plant in a garage or unheated porch, that’s the temperature you need to avoid. Note small containers also have water issues with the soil drying out plus the soil freezing and this is a double dose of death.

Old age.

Many beginning gardeners don’t understand that the lifespan of a perennial isn’t “forever”. Most perennials live 3–5 years before they go to the great compost heap in the sky. The longer-lived ones (peonies, daylilies, hosta, astilbe) can easily reach 15–20 years but most others are shorter-lived.

In my perennial garden, I plan on losing 15% every year just “because”–with no reason other than “it’s dead”.

Who knows but everybody loses this one

In the nursery trade, we know that winter will kill a different plant every year. Some year, the unique pattern of weather might wipe out Shasta daisies. The next it might be bleeding heart. This won’t happen in every garden but there will be a general regional plant loss that will mystify every garden expert and cause a run on that plant in the garden shops. Plants that are otherwise bone-hardy will suddenly die with no clear reason. But it sure annoys the heck out of gardeners.

What can gardeners do?

Mulch helps even out the swings in temperature and it also helps hold the snow over top of the plants. You’ll lose more plants in a year with a fluctuating spring (from high to low and up again) than you will in a year where everything stays frozen until it is time to grow. While keeping my plants frozen a little longer with a thick mulch may mean the early spring bloomers are a few days late blooming, I know they are alive.

One of the greatest “mulches” for tender perennials is to put old Christmas tree branches over top of the very tender plants. This holds the snow in around the plant and keeps them happy until spring. Remove the branches when the snow melts.

How to think about your perennials in the spring

Do not give up on a plant until you know the plant. For example, every year I’ll get letters asking why this plant or that plant is dead. And I write back suggesting they wait another few weeks because the plant is a notoriously late starter (Coreopsis verticillata) or just sulking a little (Hibiscus).

When I moved, put my Hibiscus in a holding garden in October 05 and then to its garden location in April 06. It finally showed up in early July with two shoots, grew six-feet tall in 6 weeks and started blooming the end of August. Go figure. Even I had given up on this one but it surprised me.

If you’re poking around, you can check to see if the root is soft and mushy (dead) under the mulch or whether the root and eyes (small growing points) are hard (alive). If a lavender or woody plant, you can gently scrape the bark with your thumbnail and if it is bright green under the bark, it is alive. If brown, that branch is dead. Enough dead branches and the plant is dead.

You can get a ton of my gardening tips and information right here

Often it’s something the gardener does…

This always assumes that you put your plant in the right light and soil areas. If you try to grow a plant out of its preferred location, you stress it. If you stress it enough, it will winter-kill. So clay soils that hold moisture will rot out roots of plants that want drainage. Plants that want full sunlight and are planted in part sun will go into the winter weakened. I note you may get away with this for a few years but eventually, the stress of the growing condition will show itself over the winter.

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Everything You Need To Know About Perennial Plant Division

To begin with, when it comes to perennial plant division, most perennials need renovating (plant division) every 3–5 years. Some such as garden mums need it every year while the really hardy ones like peonies, hosta, and daylilies rarely require renovating.

Echinacea ‘Cheyenne Mix’
Echinacea ‘Cheyenne Mix’ image the author

You can tell if your perennials need renovation by looking for the following symptoms.

  • There are dead spots in the plant base.
  • This is common on mums when they are not divided regularly; all the new growth is concentrated in the outer edges..
  • Your plant did not flower very heavily this year. Iris are a good example of this; once there are too many fans in the plant, they crowd each other out and compete for nutrients — reducing the flower numbers..
  • Sometimes, overcrowding will also lead to smaller flowers than normal. The symptoms all come from overcrowding of the roots and too much competition for available nutrients. As you suspect, the remedy is to divide your plants and space them out..

When Should Perennial Plant Division Be Done?

Spring or fall.

The rule of thumb says that if it blooms in the early spring, divide in the very early spring before bloom or do it in the fall. If it blooms in summer or fall, divide it in the spring

This is for best results (although you can do it in the fall as well)


In my experience, if you need to transplant perennials in the fall — the best time in USDA zone 4 to transplant perennials in the fall is September (but note my overall favorite time to transplant perennials is in the spring)
 After September, the plants may not get enough time (6–8 weeks) to establish their roots and get settled before cold soil starts to retard their new root growth.

  • For every zone warmer than zone 4 you can delay the last date of transplanting/dividing by a week.
  • So USDA 5 should be finished fall perennial work by the end of the first week in October.
  • USDA 6 should be finished by the second week of October.

Later Than That

Plantings done later than September have reduced survival rates in my garden.

One problem for the beginning gardener is that in early September, the plants still look good and undamaged by frost and it seems a shame to cut them down to divide them.

Do it anyway. Your plant will thank you next year with better growth and flowers. Yes, they will look bedraggled as soon as you go at them with the shovels and shears but that’s the price you pay now for next year’s blooms.

Spring Division

Real beginner gardeners divide plants as soon as they poke their young shoots up through the ground. In this way, you can see where you’re digging and what size of offshoots you’re going to take.

Note that this will mean there’s no single best time to do spring divisions for the beginning home gardener following those timelines. As your plants start to grow, you start to divide.

Experienced gardeners dig their perennials as soon as the ground thaws (all perennials are dug then) and do divisions then. You can see “eyes” or future growth points on perennial roots then and divisions will work quite nicely at this time. The only thing is that you have to have faith that your plant is alive (and sometimes they aren’t). 😉 This is an experience kind of thing.

My advice is to dig when you see the plant starting to grow if you’re unsure of yourself. Get a bit of experience. Then start digging as soon as the ground thaws out for most of your dividing.

Or. Do it when you have the time. 🙂

Just don’t do it once the plant has started serious growing and is throwing out leaves as you may set the plant back (or kill a weak one)

There are two ways to divide perennials:

You can do it the hard way or the easy way.
 Now, the hard way often recommended by gardening authors that don’t know any better, is to dig and pry the plant apart with two gardening forks turned back to back. This is dumb and way too much work. Do NOT do it this way.

The easy way and the way used by virtually all commercial growers is simply to dig up the plant with a shovel and chop it up with the same shovel.

No gently prying, no careful sensibilities of plant health, just whack it in half with a sharp blade.

Sometimes, with plants such as Veronica or other small clump forming plants, the plant will easily come apart in your hands after it has been dug up.

Others such as Aruncus will almost need a chainsaw to get an established plant into pieces.

Let me suggest that when the plant (or plants if you are ambitious) is out of the ground, it is the perfect time to renovate the soil in the garden.

  • Put the plants on a tarp or in a wheelbarrow and cover them so they will not dry out.
  • Add several inches of compost to the garden bed by spreading it over top of the now-empty areas.
  • Turn these areas over to at least one shovel blade length deep — approximately eight inches in depth.
  • The deeper you turn over the soil, the easier a time the plant roots will have in their reestablishment.
  • If you are only working with one or two plants, add the compost to that planting area and turn it over as deeply as you can.
  • Do not be concerned about the roots from neighboring plants that are in the area; do not hesitate to cut them or disturb them as they’ll recover quickly enough on their own.
  • Once the bed has been dug and the newly arrived stones and persistent weed roots have both been removed from the garden, the perennials can be replanted.
  • Extra plants from the dividing can go into a new bed or can be given to neighbors.
  • Put the plants into the soil at the same depth they were at when you divided them. Hint: Iris rhizomes can be laid on the ground and the roots buried in a trench while peonies should be replanted so their eyes (the pointy things for next year’s growth) are just below the surface if you want them to bloom again. Too deep with either plant and you’ll not see blooms again until you divide them the next time.

I sometimes get asked how long the plants can be left out of the ground during the renovation? If they are kept cool (put them in the shade) and dampish (cover them with an old damp sheet or wet newspapers and spritz them with the hose once a day) they’ll keep for several weeks. As long as you do not leave them out in the sun to bake, they’ll be fine.

Do cut back the foliage on the newly-moved plant by at least one half to three quarters. They do not require it to set new roots and this foliage will only lose water while the plant is waiting to be replanted.

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