Preparing clones must be taken very seriously, as your clones represent your final product, just as much as the blooming plants do. Many growers make the mistake of inadvertently paying very little attention to their clones and young plants, in favor of giving more attention to the blooming plants. This is a systemic problem, which later catches up with the grower, especially if mother plants are not used, and clones are taken from round to round.
The first step in preparing healthy vigorous clones is a flush and re-fill of nutrients for the plants which will donate the cuttings. Clones should be taken near the end of the veg cycle, when the plants are almost ready to move into bloom. So these donor plants have many growing tips to use for clones. The fastest rooting clones will be actively growing tips. You can identify actively growing tips by the lighter green color in the center of the growth tips. By re-filling the nutrient solution, the plants are getting a fresh batch to the tips which will be used for cuttings to make roots in their early days.
The lower branches of the plant DO NOT make good clones. They are not growing as quickly and therefore do not root as quickly. This allows them to turn yellow before rooting, which tells us they have used their stored food. So if clones are yellow, and there are no roots, they are stunted. There arent any roots to get food, and there is no food left in storage inside the clone leaves. Clones in this state may eventually root in several weeks, or may never root at all. This is one of the VERY few times that foliar spraying a light nutrient solution may help them to get going.
A couple days after re-filling the nutrient solutions, prepare a few drinking glasses, nearly full with water. Use cold water from the tap, never hot, but also do not let the cold run VERY cold. If the water is already running VERY cold, allow the glasses of water to warm up a little first. Use a thermometer if handy to make sure the water is above 15c before proceeding.
Next prepare some scissors by washing them with some regular antibacterial soap. Very clean scissors and hands make sure that foreign materials are not getting into the cuttings. Avoid razor blades with oils on them.
Go ahead and cut the top most active growing tips of the donor plants. Cut approximately 4 inches of stem and then cut off any leaves on the stem except the top pair. If the top pair of leaves is small, then leave one extra leaf from the next node. If the top pair of leaves is too large, you can trim the leaf tips down. While you should not cut too fast, the cutting should be placed in a glass within 10 seconds or so after cutting from the plant. Make sure that the glasses are placed in a shaded are of the veg room, usually in the shadow of something else, so there is no direct light on them, only reflected light from the walls. If your clones wilt at all, there is too much light getting to them.
Leave the clones in the water glasses for at least 24 hours, but not more than 48 hours. Leaving the cuttings in a glass of water first avoids getting an air bubble in the stem, and second gets the outer stem weaker, ready for roots to pop. So in other words, some time on the second day, you need to pop the clones into rockwool cubes. I highly recommend using starter plugs that already have a thin punched hole. If using non-punched cubes, then use a nail or screw to make holes. Get the cubes thoroughly wet, just short of dripping wet. Without using hot water, make sure the cubes are not VERY cold.
Prepare by washing your hands for sterility, and get your rooting powder out. Take each clone one at a time from the water glasses, and dip the end in the rooting powder. Knock off any excess powder and push into a wet rockwool cube. While not using excessive force, a little bit often doesnt hurt. The main thing is not to kink the stem, or collapse the stem with finger pressure. Do NOT worry if the clone stems are curled when taking them from the water. Dont try to straighten them, because they will straighten on their own as the stems dry up. The reason they curl is because the outer stem contracts differently than the inside stem when it soaked wet. If you straighten the clone while still wet, the dried clone stem will be curled the other way.
Leave the rockwool plugs or cubes in a tray, with a little standing water so they dont dry out, and make sure they are still under a shaded area of the veg room. You MUST also make sure that the tray is not on a cold floor, in fact, the warmer the better for clones to root. Use a dome lid to keep the moisture content high, however you MUST open the lid once or twice a day to exchange the air for new air. Leave them in the dome for three days.
Now remove the dome lid, and make sure the cubes are still sufficiently moist to not dry out. The clones can be taken out of the shade, but still several feet from the lamp. Allow another 3 days before transferring the clones into an actual system under the lamp. The system should have a light concentration of food, about strength, and the bottom of the growing baskets should be just barely (eight to quarter inch) submerged in the water, or drip emitters to each plant. At first, keep the lamp twice as far away as normal, and as the cutting show their first couple inches of roots out the cube bottoms, you can lower the lamp towards normal distance.
After roots are approximately two to three inches long, you can increase the food content to about strength. Congratulations, your clones have become plants!