Fall perennial care, updated for 2024

Fall is a busy time in my garden, with lots of cleanup and planting for next season to get done. We typically have around 6-7000 tulip bulbs to plant, plus other bulbs like alliums, and usually a few new peonies too. While it’s exciting to think about the new flowers that will come from these investments, my garden is full of existing plants that need attention too each fall. I’m talking about the perennials that make up the backbone of my garden. I rely on these plants to provide a steady stream of blooms from late May until early September each year. They fill such an important role on my farm, bridging the gap between early bulbs and summer annuals, and then again in late summer and early fall when many of the tender annual flowers have died due to frost. They are true workhorses in my garden, so they deserve extra care before they go dormant over the winter.

Here are the steps I take to make sure my precious perennials stay healthy:

1) Water, water, water. Drought really weakens plants, shrubs and trees and although we have had a good year for rain, we are still not recovered from the last three years of historically low precipitation. Plants that go into winter in a stressed state due to drought are much more likely to die from winter kill. It’s easy to underestimate how much moisture a mature shrub or plant needs. They have extensive root systems that require a lot of water. If there is a lot of rain in September and October, you can feel assured that your plants will be okay for moisture. Unfortunately, this is not the way the climate is trending these days. That means you most likely need to water throughout the summer and especially before the ground freezes. The amount of water you need to apply will depend on the type of soil you have, but you need to water until the top six to nine inches of soil under your plants feels wet. In my garden, I’ve gone to plant after what I thought was a good rain, only to find the soil dry an inch down. It takes a lot of water to give the root zone a good soak and the only way to know is to get out your trowel and dig down near your plants and check the soil.

2) Check for disease. Go through your garden and check all your trees, shrubs and perennials for signs of viruses, damaged limbs and pest problems. This is so much easier once the leaves have fallen. Prune branches and sterilize clippers in between cuts if you see black knot or other fungal disease on shrubs. Dig up and put diseased perennials in the trash, never in city or home compost. I have some peonies with Tobacco Rattle Virus that appeared this year, after 4 years of tending them from new plants. It’s really disheartening to throw away plants, but if you don’t, you risk the virus or disease spreading to your whole garden.

3) Move and/or divide perennials. If you have plants that are at least three years old and have never bloomed or are underperforming in other ways, consider whether you’ve given them the best place to thrive. A plant that requires semi-shade may have been able to cope with full sun in years past, but not with the increasing heat of our summers. Check online to see how much sun, moisture, and drainage your plant requires and move it to a better spot in the garden. Really mature perennials do need to be divided to keep them healthy as they will outgrow the space you’ve given them and start to die off. Peonies should be divided every 10-15 years. September is the best time to do this as nighttime temperatures have cooled and with good watering or rain, perennials will transplant well. Cut back foliage before moving so the plant can focus its energy on root growth, not maintaining green growth. If you don’t get around to it until October, don’t stress! I have planted until late October with good results still.

4) Once you’ve got everything in it’s new spot, give all your perennials a top dressing of fresh compost. I’m also giving my perennial beds a sprinkle of dried comfrey leaves this year. This plant grows in my garden and is a bit of a beast. I try to keep it under control by harvesting the leaves frequently and using them as a homegrown fertilizer. I am working hard to minimize off-farm inputs, like purchased fertilizer. Comfrey leaves contain high amounts of plant protein, plus good amounts of all three major plant nutrients ( nitrogen, potassium, and phosphorus). It has a very deep tap root that can extend 10 feet down into the earth and extract all the trace minerals that other plants can’t reach. When it’s threatening to take over my bed, I rip out all the leaves and dry them in my garage, then crush them into a powder. Before a rain, I will sprinkle it on around my perennials to give them a nutrient boost. This sets your plants up for good growth in the spring once the snow melts. Knowing your perennials are set for another season is one less thing to worry about in the busy spring season.

5) Weeding is never at the top of my list of fun things to do, but since 2023 and the worst Aster Yellows infection my garden has experienced, I have added it to my list of “must-dos” for fall. Aster Yellows will overwinter in perennial weeds like dandelions and Canada Thistle, providing an early infection source for the leaf hoppers that spread the disease to garden plants. Of course, I will never win the war on dandelions but I am much more aggressive about removing as many as possible from all my tunnels and perennial beds, especially those with susceptible plants like Echinacea. After losing more than 60% of my garden to Aster Yellows in 2023, I am willing to do a lot of weeding to avoid that same fate.

6) Remove all debris from around the plants if you grow lilies. Do not mulch lilies. A top dressing of compost is good for them but you want bare soil under them to prevent lily beetles. They hide in debris and emerge in the spring to damage lily plants

7) If you have plants that are not quite hardy to your growing zone, the last task you need to do before the ground freezes is give them some extra winter protection. In early November, just as the nighttime temperatures start to seriously drop, I give things like lavender and my cloned echinacea a thick layer of barley straw or spruce branches to form a blanket. Use whatever organic mulch you have on hand, as long as it can be easily removed in spring when the soil warms. This is really important in years when we don’t get adequate snowfall in winter, or when it all melts during a warm spell, leaving your plants exposed to the next cold snap.

You’ll notice I didn’t mention cutting back perennials in the fall. That’s because I don’t! Any branches I haven’t harvested for dried flowers, I leave on the plant. The stems serve as an important winter shelter for ladybugs and other beneficial insects. The base of leaves helps catch and keep snowfall, protecting the roots. I wait until the nighttime temperatures are staying above 10 C in spring before I go around and clean up last year’s growth. Then I know it’s warm enough for our insect and pollinator friends and I’m not disturbing their winter sleep.