How to Force Forsythia Stems

Keep a diary of daily temperatures beginning in late fall to know when eight weeks of temperatures below 40 degrees Fahrenheit have passed, so you can start to cut branches. Typically, this date is after January 15, according to the University of Illinois Extension.

Choose branches with a lot of round, plump flower buds, which are larger than narrow, pointy leaf buds, the Iowa State University Extension notes. Shoots at the top of the forsythia bush tend to have closely packed buds. Selecting branches can be a part of the plant's annual pruning, but only select branches for forcing that won't destroy its natural shape. Have a bucket of lukewarm water outside with you and make slanting cuts, at 45-degree angles, 1 to 2 feet from branch tips with clean, sharp hand shears. University of Illinois Extension horticulturist Greg Stack recommends cutting into branch ends in a cross or star shape to allow water to be absorbed faster.

Remove side branches and buds that will be submerged in water to prevent rot, and immediately place the branches in the bucket of water. Once in the house, lay the branches in a bathtub of lukewarm water and leave them there for several hours. This provides the stems with adequate water and softens the scales covering flower buds, which helps the flowers to show more quickly, according to the University of Illinois Extension.

Place the branches in a tall container or vase of water and keep it in a cool location, between 60 and 65 degrees Fahrenheit, that does not receive a lot of light, according to the Iowa State University Extension. As the branches are cut off from the plant's roots and, therefore, nutrients, providing adequate water is a must. While forcing, mist the branches two or three times daily to prevent the buds from drying out. A daily change of container water during and after forcing prevents the growth of bacteria and fungi.

Move the plants to a brighter area when the flowers begin to bloom, but avoid direct sunlight and heat sources. The University of Illinois Extension's Greg Stack recommends keeping the forced branches in a location at night with temperatures between 40 and 50 degrees Fahrenheit to extend the flowers' life.