Fall Planting Hardy Annuals and Biennials for Spring Blooms
The best time to plant hardy annual and biennials is when the summer heat has left, but before the season is over. It’s a very narrow window of time for most people, but with a bit of planning you can make sure that you plant at the ideal time.
But when is the best time?
Too soon, and your plants won’t do well. Cool season annual flowers like cool and moist conditions to grow in, and if temperatures are too hot you may find a lot of issues with growing them including finding it hard to establish, a higher disease rate, and other issues that come with warmer weather.
Most importantly, it’s important that your plants haven’t grown too large. Plants that are too mature - more than just small seedlings - won’t overwinter as well, and you’ll find more frost and freeze damage to the more mature leaves and stems.
It’s a little known fact that smaller seedlings will overwinter more readily, especially with a little bit of shelter from windbreaks or leaf mulch or floating row cover. Larkspur for example is the most winter hardy when it is in the stage of 1-2 sets of true leaves (the leaves not including the cotyledons or seed leaves) and so it is best to plant out your seedlings as growth slows down for the season.
On the other hand, you don’t want to plant too late - if too late in the season, your seedlings can’t get established and may not survive the winter. Or in the best case scenario, your seedlings may not die - but they won’t have time to get their roots established either, which means that you miss out on your advantage of fall planting.
For us there are around two months that are ideal for fall planting - October and November primarily, with a bit of leeway on both ends of the season. The reason for this being the ideal time for fall planting falls on two interactive factors:
Hours of daylight
Temperature
I’ll get into a little bit of why these two factors are really important in a bit, but it’s important to also note that your months for fall planting may not be the same as us. I’ll show you how to calculate your ideal planting dates later on.
HOURS OF DAYLIGHT
Most plants won’t grow when they get less than 10 hours of daylight. So when your hours of daylight are less than 10 hours, your plants won’t grow - they’ll just sit there.
To gain the advantage of a fall planting, you should plan on getting your seedlings planted prior to the hours of daylight dipping below 10 hours.
How to calculate your hours of daylightUse a website like Time and Date to calculate your hours of daylight based on the date. You’ll be able to track and see when exactly your hours of daylight drop below 10 hours.
For us, that date is approximately December 1st (although it starts technically dipping down below 10 hours in the last few days of November) which means that we have approximately two months to get our seedlings into the ground, provided it stays warm enough.
TEMPERATURE
Warmer temperatures are needed for plants to grow. Although plants can still grow at cooler temperatures, they grow the most quickly and robustly when temperatures are at least 40 F, but much better at 50 F or even 60 F.
Depending on your environment, you may find that the temperatures may stay warm enough to continue growth. We’re lucky enough to have plenty of sunshine and very warm days all the way throughout the winter.
If your weather isn’t quite as warm, you can help keep your plants warm enough to keep growing by covering with some floating row cover (such as Agribon) - it will help to trap heat and create an artificially warm environment for your seedlings to grow in.
How to calculate temperatures
To calculate your average temperatures, you can check out a website like Weatherspark to see when your temperatures start to dip below 40 F. To be honest, we stay pretty warm in our environment, and the amount of sunlight really helps to increase the temperatures during the winter, but in more northern climates it is important to note the temperatures to ensure you’ll have enough heat to grow your seedlings.
I hope this helps you with your fall planting plans and understanding how it all works
Fall planted annuals and biennials are some of the most beautiful and robust flowers you can grow for your cutting garden or flower farm. Even if you are able to just plant some of the most hardy flowers - sweet peas, foxgloves, daucus, icelandic poppies, dianthus, violas/pansies and rudbeckia - you’ll find it helps you to have flowers sooner, and some of the biggest, tallest, most beautiful flowers you have ever grown.
If you’re interested in planning your cutting garden or flower farm for spring, here are a few articles you may be interested in: