WHEN IS TOO LATE TO PLANT NATIVE PERENNIALS?
Not all of the Autumn season is for planting friends. In this post, learn how to prevent your perennials and shrubs from dying overwinter with simple tips of TIME & SOIL TEMPERATURE!
“Fall is for planting”
is the motto of every smart gardener and plant nurseries.
But what does that REALLY mean???
Friend, that simple phrase does NOT catch all the nuances of Autumn planting!
And if you are new gardener it’s a problem phrase!
Seriously! Does it mean you can plant annuals like zinnias in November? How about perennials on Thanksgiving weekend?
Let’s take a look at TIMING for an example.
The SEASON of ‘Fall’ spans from September 22 to December 21…
Does ‘Fall is for Planting” mean you can still plant a perennial in December?
Sure the ground is frozen but you could dig it with an auger to get the plant in the ground. That is if you have time between all the holiday parties! Ha-ha!
So it really doesn’t have anything to to do with the calendar.
Heck, not even the old standby of your ‘last frost date isn’t as reliable due to climate change!
Some say “oh you can go by your growing zone”… hmmm friend you can but even that has a few ‘speedbumps”
First let’s look at your planting zone…
To find your 'Zone' visit https://planthardiness.ars.usda.gov/
Based on how cold your area is determines which Plant Hardiness Zone you are in. It is a guide to determine which perennial plants are most likely to thrive at a specific location.
How does this play out?
In November, a gardener in Virginia in Zone 8 has vastly different growing conditions from one in Quebec in Zone 3!
Just goes to show that one gardener's Winter is another gardener's Spring!
Psst…in this post, I’m focusing on perennials only and in Zones 4-5 of eastern Lake Ontario and Central New York.
Now say you know that you’re growing plants in Zone 5. You’ve looked up your first frost day of October 12. To find the ideal time to plant native perennials in Autumn you’d count backwards 6-8 weeks.
Friend, those ‘frost dates’ are guides.
We need to consider your region, local environment plus changes from climate change etc.
Let’s look at our farm here in Mexico, New York for example.
Technically we are in Zone 5. Last year our last frost date was estimated at May 17. (It was April 20).
First frost of Autumn is October 7th.
Now our farm is 4 miles east of Lake Ontario. A great lake is famous for giving epic lake effect rain and snow storms
Why, our frost dates could be SNOW dates for goodness sake!
It’s happened more than a few times!
What’s a habitat gardener to do?
Before we jump into the ‘weeds’ of Autumn planting;
WHY is planting perennials, shrubs and hardy annuals in Autumn is the BEST time to plant.
First think back to your Spring gardening.
Let’s say in Spring around late May, you bring home 3 beautiful quarts of Anise Hyssop (Agastache foeniculum) a native perennial.
You plant them in the perfect spot. Full sun and well draining soil. You keep them moist for two weeks while they settle in…
Now those plants will be fine but they will need watching over through Spring rains and Summer heatwaves.
Why?
Because their roots are not fully established.
Meanwhile you and the pollinators wait all Summer for the plants to bloom.
You’ll be waiting for that Anise Hyssop to grow past their ‘sleep’ year when they are establishing roots BEFORE putting out foliage & blooms for wildlife.
‘SKIP’ the wait NOW in Autumn to see blooms next Spring and Summer
Planted in Autumn these same plants would be BLOOMING for you AND wildlife next Spring!
Why?
Planted in Autumn, perennials can establish their root systems deeply and then ‘sleep’ over the Winter. Then they can BURST into their 2nd year of growing foliage in very early Spring and blooms in Summer!
But here’s the catch…
THERE’S ALWAYS A CATCH…
There is a ‘trick’ to Autumn planting. It’s one you need to know: SOIL TEMPERATURE!
Just like in Spring planting, soil temperatures play a leading role in whether or not your plant survives the coming season. In this case WINTER!
At my farm east of Lake Ontario– plants must survive bitter cold air temps into -20F in January plus wind, rain, and let’s not even get into HEAVY lake effect snow that can fall 10’ in a week and sometimes a few days!
SOIL TEMPERATURES are what I use to decide ‘How late is too late to plant perennials’
This chart is my go-to for Autumn planting!
That blue line shows how fast soil temperatures change! In mid-September they were in the upper 60s.
Just 2 weeks later, soil temperatures are down by 10 degrees into the lower 50s!!!
This is why the BEST time to plant perennials in Autumn is 6-8 weeks BEFORE your frost date!.
Ideal soil temps for root growth are between 50* and 70 degrees.
To measure your soil temps just use a soil thermometer.
No fancy tools needed, Friend. You can even use a meat thermometer! Just be sure it measures down to 40*
BONUS TIP: When taking soil temperatures be sure you measure the temperature of the depth your plant will be planted! For example: your plant is a quart size plant 6” deep so you’d insert the thermometer to 6 for the soil temperature at the depth the roots will be.
If soil temps are still in the 60s in November your perennials like that lovely Anise Hyssop will be growing strong roots!
But should you plant perennials in November?
Friend this is VERY risky for your lovely plants…
By November they will be phasing into dormancy for the Winter. Air temperature, rains, and the frosts will negatively impact your new planting. AND ABOVE GROUND IS NOT WHERE THEY SHOULD BE!
So how late can you plant?
This is the question I’m being asked several times a week!
Regardless of all the above factors~ yes even the soil temperature:
ALL NATIVE PERENNIALS NEED 6-8 WEEKS to establish their root systems BEFORE the ground BEGINS to freeze!
Why? Just as we begin to ‘cozy up’ and prepare for Winter, so do plants.
They need to get settled in and ‘cozy’ before entering dormancy for the long Winter.
As they enter dormancy…
Many native plants develop dried seeds for creating next years plants and feed overwintering birds!
The science of Autumn & plants
Plant dormancy doesn’t just happen. It’s a process of amazing reactions!
A plant's hormones respond to environmental changes of Autumn like the angle of the sun, shorter hours of daylight and changes in soil and air temperatures.
The plant's response is to slow down photosynthesis and respiration. As this happens the foliage dies back and the plant relies on stored carbohydrates and nutrients in its roots for surviving the Winter and to begin initial growth of foliage in Spring.
Once dormant, cold air and soil temperatures also slow root growth.
FUN PLANT FACT: Did you know plants create their own ‘antifreeze" ?!? Plants adapt to Winter’s temperature fluctuations by controlling when and where water in their cells freeze! Plant cells accumulate and concentrate substances like sugars and salts to decrease their freezing point to protect the cells from freezes!
Once dormant, plants use the ‘antifreeze’ to protect their cells however it’s only effective when air temperatures are between 32 and 20 degrees fahrenheit.
This is why Nature provides the extra blanket of fallen leaves and snow cover as protection against colder temperatures of Winter. (Hence why we have more perennials die in years when there is less snowfall!)
So when should you plant perennials in Autumn?
For the best Winter survival of your native perennials, plant them 6-8 weeks before soil temps reach 50* or less.
Think early September when soil temps are in the 60s for 6-8 weeks before the cold Autumn days begin.
This gives your plants time to establish roots BEFORE dormancy begins…
But let’s say you missed that boat….
WHEN IS TOO LATE TO PLANT NATIVE PERENNIALS?
Look I get it~ we get busy with LIFE. Every gardener forgets the plants they brought home.
We’ve all done it– go ahead, let's see a raise of hands. Who has ever had a pile of plants in pots desperately waiting to get planted. Only to be forgotten until they are dried up and possibly dead.
You can’t ‘see’ me but I’m over hear waving frantically! Ha-ha!
(One advantage of plants from our farm is that being wrapped in burlap you plant them right away!)
Back to this lateness my friend…
Let’s take a lesson from my own mistake here at the farm…
Early last November, I spent 5 days planting plugs and quart sized plants into a new garden bed just made with extra compost.
It was raining, air temps were in the 40s plus we had a few frosts.
I spent those 5 days soaked, cold, and covered in mud trying to get all my plant into the ground.
The only thing going for me besides a thermos of hot tea was soil temperatures.
Despite the cold air temperatures, soil temps were in the 50s due to the warmth of the compost pile and the garden's location by the road in full sun.
Not that November has much sun!!!
Once I planted the garden I watered as needed and waited for signs of dormancy ie foliage drying up. Then and only then when I saw dormancy did I cover the plants deep in fallen leaves and brush to hold the leaves in place.
If you’ve visited the farm this year you’ve seen how magnificently this turned out!
Did I take a risk– oh you betcha!
All those plants could have easily died and the work would have had to be repeated in Spring! To be clear I do NOT recommend this tardy approach!!!
If you missed the ‘perfect time’ of September planting in Zone 5-6 there is a 2nd option: get your perennials into the ground BEFORE mid-October!
Soil temps are still GREAT in the 50s for planting.
But Make no mistake hard frosts and deep freeze is waiting right around the corner in November!
You can even see your soil temp forecast HERE
Planted in early October your plants should still have a few weeks to get those roots settled in!
Take your soil’s temperature then get to planting! Water in for a few weeks then wait for signs of dormancy. Watch for the new plant's foliage to fade.
Once you see signs of dormancy, protect the plants from Winter-kill by covering them with fallen leaves and brush.
After all that hard work
You can enjoy the beauty of Autumn
Enjoy watching the birds hunting through the fallen leaves.
Catch more sunsets by the lake.
Or just chill in your favorite hammock. Sit back, relax with a book and sip cocoa knowing you’ve done your best for your new plants.
And you can smile to yourself. Simply because it’s November and you are not in the garden on a cold windy (possibly rainy or snowy) November day rushing to plant your plants into frozen ground!
Take it from me… November planting is not very pleasant!!
