I have been requested by several web sites to remove the information below. They don't think the end-user should know how to make more trees or bushes from the ones they already have. They feel he/she should just buy more. I feel differntly: everyone has the right to know how to do it, so, here it is.
Depending on when you take the cuttings, they are called differently. These particular cuttings are called hardwood cuttings and are taken only when the trees are dormant.
This information is only for the homeowner, the person who wants to duplicate some of his plants. If you want to make thousands of trees and/or sell cuttings for the next 6 months, then you need much more information. Please download my e-book, it is $9.95, send me email and I will give you the name of the file to download.
Timing is most important. The cuttings must be taken only when the plants are dormant. In the Northern Hemisphere is it between November and February. If you live in a place like florida or Texas where it does not get cold enough for the leaves to drop, then do this in February which is normally the coldest month.
The information I am giving you relates to hybrid poplars, however, it can be used with many other plants, willows, perennials, etc. Let's say you have a hybrid poplar tree which you want to propagate. Wait until the tree is dormant (no leaves) and take a short branch from it. The branch will have many buds along its surface, spaced between 1 and 2 inches apart . That is a 1-year branch. Those buds are what is going to grow. Cut that branch into a short piece with only 2 of those buds, now you have a cutting. My cuttings will have a minimum of 2 buds. I have tried making cuttings with only 1 bud, believe me, it does not work.
The cutting has 2 buds which are pointing in the same direction. The bud which points away from the cutting is the top bud. That is the one that will grow. Dip the bottom of the cutting in rooting hormone and put it in the soil so that only the top bud is showing out of the soil. This soil can be outdoors, or in a container of some kind. Water it and you are done. Keep the soil moist but not wet. The cutting will start growing when the temperature and light are appropriate. Most trees require about 65 degrees and at least 14 hours of light daily to germinate.
Once it germinates, keep the soil moist. If the tree is growing very skinny, it is not getting enough light. If it grows too slow, or not growing at all, temperature is too low.
If you are growing several cuttings close together, you may experience what is called "Damping Off" which is a virus that attacks all plants at the same time killing them overnight. To prevent this from happening, either, give the cuttings more growing space, or add a small fan to gently add air circulation around the cuttings.
When the plants are about 10" tall, they should be transplanted either to larger containers or outdoors. Do not transplant if temperatures are below 40 degrees or there is a chance of frost. Many poplars can be propagated by this method, as well as willows. I have done it with Spirea plants, American Beautyberry, Figs, Rose of Sharon, Forsythia, and many others.
If you want to, you can use longer cuttings. It will require that you prep the cuttings so they do make roots quickly. Let's say you have a 3 ft. cutting. Scratch the lower 3" of the cutting with a dull knife until you see green. If you see tan, you are scratching too deep. Prepare a hole in the ground, about 6" deep. dust some rooting hormone on the scratched part of the cutting and the bottom. Put the cutting in the hole, back fill, water and you are done. Yes, as long as you do this when the trees are dormant, it will work.
The longer the cuttings are, the more you have to scratch and the deeper the hole should be. For a 12 ft. cutting you want a foot deep hole and you want to support that cutting with a bamboo cane parallel to it and tied so the cutting does not sway with the wind. The support does not have to be too long, 3-4 ft. tall will do it. Support can be removed a few months after the tree starts growing. Information on how to keep your cuttings viable for 6 months is included in the ebook which you can download here. It is 4 pages and costs only $9.95.