How do you force cut branches to bloom in winter? Here are 4 things to try

OK, we’ve had plenty of cold. We endured several weeks of the Ohio Valley gray. And now we’ve even had that annual meanie joke of a sunny, warm February week that is a bit like Florida sticking its tongue out at all of us who live and garden in the mid-latitudes.

We all know it’s nowhere near spring. We all know there’s plenty of cold weather left to come. But oh, that tantalizing bit of sun and warmth. A meanie joke, indeed.

But every meanie joke and every bully’s bluster is nothing but a chance for a well-planned and perfectly executed retort.

There’s precious little out there flowering in the garden that doesn’t have an even greater impact if you can bring it inside. And if you can coax it into doing its thing inside at a time of year when it isn’t showing off outside, all the better.

Forcing cut woody stems into bloom this time of year is not just about a little color in the dining room. It’s a lifeline to get us from the last of the holiday poinsettia and amaryllis blooms to the first of the forsythia out in the garden.

And it’s not rocket science.

For successful forcing of cut woody stems there are just a few simple guidelines. It can take a little experimentation to perfect your system, but experimentation is what gardening is all about.

How do you force branches for winter blooms?

We know most plants that live in middle and northern latitudes go dormant in the fall. They shut down most of their activities and many shed their leaves, all to get through the winter and be ready for the coming spring. But did you know that most of these plants need the cold to complete the march of dormancy?

Most woody plants growing in areas that see cold winter temperatures need a minimum number of days and hours of cold temperatures to be able to resume growth when exposed to warmer conditions. A red oak tree moved into a warm, sunny greenhouse at the beginning of January won’t start growing because its surroundings just improved. It will likely just sit there and do nothing.

It hasn’t had enough cold.

Most temperate woody plants need something on the order of 1,000 to 2,000 hours of temperatures below about 50 degrees to satisfy this dormant sleep. While the specific requirement varies from one species to another, it usually takes somewhere between 60 and 90 days of winter weather exposure to break dormancy. After their cold requirement is met, they can respond to favorable temperatures by initiating growth.

If you’re looking to cut woody stems and force them into bloom inside, it’s futile to try before a plant’s cold requirement has been met. The good news? For many plants, we’re approaching that critical mark on the calendar. Over the next few weeks in the Louisville area, cuttings of some plants should respond to forcing.

What plants are best for winter stem forcing?

When it comes to selecting a good plant for winter stem forcing, one place to start is the earliest plants to bloom in the garden. Witchhazels (Hamamelis species and hybrids), quince (Chaenomeles species) and forsythia (Forsythia species and hybrids) have low chill requirements and force quite quickly indoors. Some witchhazels are already blooming outside which is a sure way to know their chill requirement has been met.

Later spring blooming species such as some viburnums and early lilacs (Syringa species and hybrids) also tend to force fairly well.

But all those mentioned are species that set their flower buds before going dormant in the fall. The buds are just sitting there, waiting for you to force them into bloom. Species that bloom on new growth (flowers produced from new growth during the growing season) such as roses, crepe myrtle (Lagerstroemia species) and butterfly bush (Buddleia species) are all but impossible to force into bloom as dormant, cut stems.

How do you trim plant stems to force winter growth?

When it’s time to harvest your stems, you’ll need a nice, sharp, and clean set of pruners. First, boil a pot of water on the stove, about 4 or 5 inches deep should be fine, then turn off the heat under the pot. Go outside and find your target plant and locate the stems with the most vigorous growth. If you can find a nice, straight piece of growth that was produced last year, that’s best. But two or three-year stems will work as well. They might just take a little longer to open.

Cut your stems at a 45-degree angle to expose as much basal area as possible. Trim any side shoots off the bottom 4 inches or so of the stems. Then, carefully plunge the bottom few inches of the cut stem into the hot water. After a few seconds, you should see a stream of tiny air bubbles flowing out of the base of each stem. Wait until the bubbles stop and then transfer the stems directly into a vase with fresh water.

The air bubble thing is the key part (though the clean and sharp pruners are pretty important, too.) When you cut a stem, the water inside the vascular tissue contracts, and air rushes in. If you then place the stems directly into your vase with water, the air gets trapped and air in the plumbing is bad for cut woody stems as well as cut flowers. The near-boiling water causes all the water in the vascular elements to heat up and expand and force the air out. \

Voila! No air in the stems.

Where should I place newly cut forced stems?

Finally, place your vase and stems in a bright area but out of both direct sunlight and the direct impact of your HVAC vents. Both will drastically shorten the shelf life of your forced stems. Then sit back and wait for the show to begin. Depending on the species you are forcing, in a few days, you should start to see signs of life, and shortly after, with any luck, you’ll have a nice vase full of spring color.

Take that, Florida!

Paul Cappiello is the executive director at Yew Dell Botanical Gardens, 6220 Old Lagrange Road, yewdellgardens.org.

This article originally appeared on Louisville Courier Journal: How do you force cut branches to bloom in winter? 4 things to try