Successful October Perennial Planting

It’s difficult to resist a great end-of-season bargain. And when the object of the savings is perennials, who can turn their back on that?  That being said, I thought it would be a good idea to share some planting tips to maximize your ROI on October perennial buys.

Plant ASAF - Plant as soon as feasible. A crucial component of successful fall establishment of perennials is soil temperature. Perennials, like Zone 5 hardy tree and shrubs, will continue to generate new roots as long as the soil temps are above 40°F. It goes without saying that you want the heaviest root system possible before the ground freezes around your new beauties.      

Amend Soil – One of the big differences between perennials and trees and shrubs is perennial root systems are much more shallow. For those of us that seem to have only a sandwich thickness of something approaching topsoil resting atop a layer of compacted clay that means there’s soil amending to be done.       

I’m suggesting that with a little extra effort and a great deal of good organic matter you can dramatically improve the soil conditions those shallow root systems will be growing in. Organic compost, manure, leaf mulch, cotton bur compost are all great ways to start improving a heavy, poorly drained clay soil. Your call - improving by amending individual holes, or pouring at least a couple of inches over the area and working into the entire bed for more of a long-term solution.      

Score Root Systems – By season’s end perennials may have been in their pots from 6 months to a year or more, based on the maturity of the plant. You’ll probably find some heavily “knotted” root systems. Once the hole is dug, soil is amended and you’re ready to plant, be sure and score the roots along the sides and importantly, across the bottom too, freeing them to explore their new home.

Plant at Proper Depth – First, no matter how full the perennial is in the pot, resist any urge to become a plant propagator. October is not the time to be tempted to do plant division. Just pull the plant out, tease the root edges free and place the plant on firmed soil so that the top of the ball is level with the surrounding surface - certainly, no deeper. The firming is important so that over time the plant doesn’t sink deeper, burying the root system and cutting off the oxygen supply.

Water –  As I write this the ground is really dry just below the surface and deeper. Water well and regularly up until the ground freezes to maximize root growth. With cooler weather (mid-70s as the high) perennials, especially mulched ones, won’t dry out quickly. How often, you’re thinking? “Tony, just give us a number.” Well, this is just a broad suggestion, but perhaps every 4-5 days this late in the season if we don’t receive at least an inch of rain per week.  

Mulch – The key here is just do it! Whatever your favorite organic mulch just put it 3” or so deep over the roots. Remember whenever you mulch, you’re mulching roots, not stems. So, make a donut-shaped mulch ring covering the roots leaving the center (the “crown” of the plant where the stems go into the ground) open to prevent winter rotting. Sorry, I don’t have a more sophisticated term but that’s what can happen when you bury the whole plant, especially with mounds of unshredded leaves – rotting and death!   

Cut back the foliage or not? I had a perennial epiphany about this a couple of years ago and have done a 180° flip. My stance now is, “If it has a rosette of good-looking foliage resting on the ground, leave it.” That way the foliage can relax on top of the ground at winter’s onset and become self-mulching. Anything that keeps the ground frozen over the winter is a positive.           

If the plant has stiff stems that can catch and hold snow in place, then let those stand. Snow is an excellent insulator and helps keep the plant frozen in the ground regardless of air temperature fluctuations.

Walk your garden periodically over the winter, particularly whenever there’s been a string of days well above freezing. Inspect those late-planted perennials that may not have had a chance to root into the ground. If they have “frost heaved”, that is, if the root ball has started popping up above ground, gently put your foot on either side and push it back down. The root systems of perennials that have heaved above and out may suffer, or even die, from dehydration or cold temperature exposure! 

What have you gained by fall planting? Great savings and plants that will be six months to a year ahead in development over their neighbors that join your landscape in 2021!