Container growers frequently ask me, “When is the best time to trim perennials for the winter?” There isn’t a simple answer to this question. I prefer to trim perennials as late in the fall as I can. This allows them as much opportunity as possible to store carbohydrates in their crowns and roots for their winter slumber. Since fall temperatures vary widely from one year to the next, there’s not a set calendar date I can tell you. If possible, wait until the first hard frost to begin fall trimming and preparing the perennials for winter. Trimming them too early could lead to more re-growth in the fall, which could require them to be trimmed again.

Several growers let the plants go dormant and don’t begin trimming and cleaning until the plants have turned yellow or even brown. This approach is often used by those overwintering inside structures and allows them to clean up the plants with their limited labor force during the winter months.

Trimming and removing the foliage prior to covering with protective blankets can reduce diseases and subsequaint losses from occurring.

It’s very beneficial for growers who plan to cover their plants with protective blankets, particularly in areas with significant snowfall, to trim them back before covering. There is greater risk of diseases, crown rots and even plant losses (as shown above) when significant amounts of foliage are covered by protective blankets. 

The other question I’m commonly asked is, “How far do I trim perennials back prior to overwintering them?” There’s also not a one-size fits all answer to this question, either. For most perennials, I prefer to trim them back to about 2 to 3 in. above the top of the containers they're being grown in. With evergreen perennials, avoid cutting them too low or don't trim them at all -- always stay above the crown when trimming the evergreens.

For most vines, I’ve found it best to allow the plants to go completely dormant prior to trimming them back. When the plants are trimmed, I generally trim them high, leaving at least 6 in. -- trimming higher is often better, leaving 12 in. of stem above the top of the containers.

With most perennials, it’s not absolutely necessary to remove the lower foliage (below the cut) before the plants resume growth in the spring – new growth usually grows past and covers the old cut stems. However, it’s beneficial to remove the trimmings or top growth you’ve cut off to prevent botrytis and other diseases from developing or infecting the crowns of the plants.Trimming Image – Pulse 37
Blanket Damage IMAGE
 Trimming Image – Pulse 37
Blanket Damage IMAGE
  

Now that I covered trimming in containers, that brings me to fall trimming in the landscape: to cut or not to cut. For the most part, I approach cleaning up the landscape very similarly as I do containerized plants with a few little nuances.

Dead flower stems or seed heads can be removed anytime. However, I still prefer to allow the perennials to die back or go dormant naturally (after a few hard frosts) before doing any major trimming. This allows as much time as the season will allow for the plants to store food prior to going dormant. When the leaves turn yellow or brown, you can safely trim them back.

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When trimming, a good practice is to snip off the stems and leaves to roughly 2 to 4 in. (5 to 10 cm) above the soil. Trimming at this height leaves short stubs, but prevents you from accidentally cutting into or damaging the crown and makes it easy to see where the clumps will emerge in the spring.

Most perennials can be cut back in the spring or the fall. However, there are several perennials -- especially the shrubby ones like artemisia, buddleia, carypoteris, lavender and perovskia -- that respond better if you wait for new growth to appear (or just prior to growing) in the spring before trimming them.

Don’t forget that many perennials can provide winter interest to an otherwise drab landscape and can be left untrimmed in the fall to provide these attributes. Other plants, such as echinacea, can be left as a food source for birds.

In most cases, the decision to trim or not to trim before winter is a personal preference and isn't an absolute requirement. 

There’s good news for KleenGrow users. The REI (Restricted Entry Interval) for chemigation application through irrigation lines has been reduced from 48 to a much more user-friendly 12 hours. This means growers can now more effectively apply drench applications for controlling soil borne pathogens, such as pythium and phytopthora, or for reducing the development of algae.

How effective is KleenGrow on soil pathogens? Check this out:

     The image above shows the results from a grower trial on poinsettia comparing a 1.0 oz./100 gal. drench of Subdue Maxx to the combination drench of ½ oz./100 gal. Subdue Maxx and 12 oz./100 gal. KleenGrow. As these results show and other research trials have demonstrated, adding KleenGrow to the Subdue Maxx drench and reducing the amount of fungicide applied with the combination of the two increased the control of Pythium by 20% to 40% when applied as a drench. Take note that KleenGrow applied by itself is quite effective on several soil pathogens.

Click here to learn more about this unique quaternary ammonium chloride formulation containing dodecyl dimethyl ammonium chloride (DDAC).

Here’s a sneak peek of a couple of recently introduced Terra Nova perennials I thought you might enjoy.

Agastache Morello

Please allow me to introduce you to Agastache Morello. It’s a very showy and floriferous cultivar with very large deep burgundy inflorescences. This upright selection grows 27- to 33-in. tall and absolutely steals the show. Pollinators and hummingbirds can’t resist ... can you? Hardy to Zone 5.

Brunnera Alchemy Pewter

Alchemy Pewter is a striking new brunnera introduction with pewter-colored, heart-shaped leaves accented nicely by prominent green veins. It has plenty of vigor, but remains compact: growing  just 14- to 16-in. tall. This great shade Zone 4 perennial also makes great-looking containers and works well in perennial combos.

Here are two new fungicides I wanted to bring to your attention:

Astun

The first fungicide is Astun from OHP, Inc. Astun is a specialist at controlling botrytis diseases. It contains the active ingredient isofetamid, which is a new fourth-generation SDHI class of chemistry belonging to the mode of action (MOA) group 7. This new systemic fungicide offers great preventative and early curative control of botrytis. Astun can be used by itself for controlling botrytis or in tank mixes when looking to broaden the spectrum of diseases controlled. Astun can be a very valuable tool to include in your botrytis spray rotations.

You can learn more about Astun by clicking here.

Pageant TR

As most of you already know, Pageant isn’t a new fungicide, however, BASF recently added this fungicide containing pyraclostrobin + boscalid to its Total Release product line. It’s marketed as Pageant TR Intrinsic brand fungicide.

Pageant TR is designed for growers looking for a quick and convenient method of applying this highly effective fungicide at any time during the production cycle. It’s effective at controlling a wide range of plant pathogens, including alternaria, botrytis, powdery mildew and many more. Additionally, the labeling allows for applications in the cargo area of trucks. This pre-shipping application provides protection during the shipping process until the plants arrive at retail.

Click here for more information on Pageant TR.

The Perennial Plant Association (PPA) is now accepting applications for the 2018 Scholarship Program. Each year, the PPA offers several scholarships (seven awarded in 2017) to students in horticulture seeking two-year and four-year degrees.

Recipients will each receive $1,000 and complimentary registration and lodging for the 2018 Perennial Plant Symposium in Raleigh, North Carolina.

I can remember how important scholarships were to me as I worked towards obtaining my degree and can only imagine how much a scholarship would mean to deserving students some 20+ plus years later. If you’re a college professor or have deserving college students working for your business, please encourage any suitable candidates to apply for the PPA Scholarships. It can make their journey a little less stressful.

Click here for the 2018 PPA Scholarship Program Application. The deadline is February 1, 2018.