The trees and shrubs that can be force into bloom are the ones that set their buds before winter and have completed a cold period. The length of that cold period varies and ends in January for some March for others. You can determine when a branch is ready for forcing by examining the buds. As soon as the buds begin to swell the branch are ready.
Select branches with plenty of plump flower buds (they are rounder than leaf buds), usually located at the top of the plant.
Cut branches 12”-36” long.
Strip off any buds that you will eventually want to put under water in a vase to reduce bacterial action.
Bring the branches inside and completely immerse them in tepid water (a bathtub is great for this). Recut the stems removing about a half inch and cut a 1”-2” slit up the end of the stem. Peel off the outer covering of bark about the same amount if the stem is very woody. Let the branches soak for at least 2 hours but no longer than ½ day making sure the ends never come into the air (air pockets will form in the water bearing vessel of the stem and prevent water from moving up to the buds.)
Place the branches in a very clean container of water mixed with a couple of drops of bleach to kill bacteria and set them in a cool place (60-65) with low to medium light.
Place a plastic bag over the branches to increase humidity so the buds will not dry out.
Change the water every few days and recut the stems by ½’ under water.
When buds begin to open, bring the branches into the room where you can enjoy them.
This will take from 4 days to 5 weeks, perhaps longer depending on the species and the stage of the buds when the branch was cut. Patience is a definite virtue at this point.
You can add florist’s preservative but it is not really necessary.
Keep the branches out of direct sunlight and drafts. They will last longer if temperatures are cool. Blooms will last about a week to 2 weeks, depending on the species.
The trick is to make sure the buds fully hydrate and cool temperatures, high humidity, and shade all facilitate that. You can force branches by just sticking them in a pail of water but the more careful you are the more successful you will be.
The list below gives the approximate time you can force each plant. The real test, however, is looking at the buds and cutting the branches when they are full and plump. I have only included ones that can be easily forced in a few weeks.
In January consider:
Forsythia (cut in early January)
Flowering cherry (until mid March)
Weeping willow (for leaves; continue to cut until March)
In February consider:
Pussy Willow (peel off the scales when you cut the branches; let the stems dry out after you put them in a vase or they will form roots and drop their blooms)
Mid March consider:
There are many other spring flowering shrubs and trees that can be forced and some with beautiful foliage. Experiment and enjoy!