JARS v45n4 - Windowsill Propagation

Windowsill Propagation
Bea MacDonald
Reprinted from the Cape Cod Chapter Newsletter

This method of propagation works for almost anything, but as rhodies are more difficult to root than most other plants, it works very well with them. It is basically the same method I was taught by Al Fordham at Arnold Arboretum almost 20 years ago, with some refinements.

POTS - With rhodies dark pots work best. For large-leafed rhodies I use 4½" pots with 2 litre tonic bottles, cut off, either top or bottom, for a cover. I also use a clear peanut butter (or similar) container (so I can see) under this and keep ⅛" to ¼" water on bottom and I water from the bottom. Three cuttings will fit nicely in this container.

For evergreen azaleas you can get in more cuttings or use a smaller container. I like 3" pots with drink glasses above and below. Plastic coffee cups can be used, with holes in one, a baggie over cutting, and second cup holding baggie in place. Works well with some things but does not absorb heat needed for root formation. Deciduous azaleas need mist so don't expect good results.

SOIL MIX - ½ peat, ½ perlite. If you have had peat around any length of time it is a good idea to sterilize soil. Fungi are the biggest cause of failed cuttings and this helps. If you are buying sterilized mix you can avoid this but I microwave my soil in large covered casserole for 15 min. Soil should be sieved through ¼" screen and moist before microwaving.

HORMONE - There are many dips and powders and different strengths. It has also been suggested that a 5-minute sugar soak helps induce rooting. The only problem with that is that it also encourages fungi growth even faster. I have had very good results using Hormex in its different strengths and this is easier for Windowsill Propagation. For hollies H-16 (or even H-8); for easy to root rhodies H-30 is about right; for hard to root rhodies H-45. Experiment. More is not always better and too strong a hormone will be as bad as too weak a one, but the powders are safer than liquid dips.

PREPARING CUTTINGS - Have sharp knife and cutting board (which can be any clean piece of board). Always cut away from you and on board to steady cutting. Cuttings should be about 3½" long plus leaves - 4 to 5 leaves. Extra leaves should be trimmed with knife, not pulled off. If leaves are extra large they can be cut in half to fit into propagation container, but remember each cut opens a way for fungi to get in. Knife should be kept clean - a small jar of ½ bleach, ½ water for dipping knife between cuts would not be amiss. When leaves are trimmed and length is proper, take a slice off stem at base about 1" long going into inner (cambium) layer. Most large-leaved rhodies should be cut on either side but smaller stemmed ones and azaleas should be cut only on one side.

Then dip in water and shake; dip in hormone and tap loose powder off. If you are careful not to get powder wet it should last for years.

STICKING CUTTINGS - You have pot filled with damp soil, firmly pressed down. Using pencil or similar tool, make hole. Insert cuttings; firm soil around cutting; water thoroughly; drain surplus water; insert label. (Do not use cutting to make hole.)

Cover with your plastic bottle and find the best location for rooting. I have a southeast bay window which works very well. Important at this point is keeping roots warm but not getting cuttings too hot or dry. It will be trial and error until you get the right combination of factors for good rooting. If you have any way of providing steady bottom heat at 70° you should increase your success rate substantially.

When your cuttings are firmly rooted remove bottle top and leave for another week. If cuttings wilt put top right back on, otherwise after a week carefully remove from pot and repot in individual pots (4" pots are good). They can then start being fertilized with ¼ strength balanced plant food.