Your clones should be big enough to reach over the top of your cup. You can cut a clone that’s shorter than 7″ (I’ve successfully cloned a stem as little as 3″ tall). However, shorter clones typically take longer to root.
I had one 4″ cutting that didn’t make roots after several weeks. Out of curiosity, I just let it keep going and refilling the cup as the water level got low. I was amazed when it finally sprouted roots 2 months later. If your stems aren’t long enough yet, follow the tips below to get them to quickly grow longer. How do I make my plant produce longer stems for clones? If the stems on your plant are too short (or there aren’t many suitable clone sites or offshoots), you need to encourage the plant to branch out and give the stems time to lengthen If you haven’t yet topped the plant, do it now (cut off the top tip of the main stem). This will cause the plant to naturally bush out and develop more side branches. Try to gently open up the plant via bending and tie the tallest branches down so all the small shoots get light and start growing.
Give strong light to your plant so all the newly-exposed shoots grow quickly But not too much light. Make sure to follow the manufacturer’s instructions on how far to keep your grow light from plants. Keeping a grow light too close to the plant can slow down plant growth to a crawl. Make sure to deal with any problems so your plant grows as fast as possible If you follow these instructions, it should only be a week or two before you have several suitable clone sites. I’ve seen some growers take 12″ (30 cm) clones or even bigger, especially when using an aerocloner. Big clones can root in the right environment and one advantage is the plants are already well developed. If you’ve got long branches and want a bunch of tall plants right away, you can often turn those branches into big clones. However, bigger clones can be more likely to wilt immediately because they have a difficult time getting water to their tallest leaves and branches. The other issue with big clones is they already have a set stem structure. With smaller clones, you have the ability to shape the size and shape of the clone via plant training, which can dramatically increase your overall yields indoors under a grow light. Step 2 – Trim the branches until there are only the top two pairs of leaves. You’re cleaning up the stems so you don’t have leaves sitting underwater in the glass. It’s easier to clean the sides of the stem now than after the clones have already been cut. Trim the branches in preparation so they’re mostly smooth. I typically leave the top two pairs of fully formed leaves, but each clone is a little different. Step 3 – Cut off your clone and immediately put in water. Don’t forget to label your cups with the name of the strain because it’s easy to forget which is which. Try to cut at a 45-degree angle, and make your cut near a node/set of leaves if possible (this may help clones root faster) Immediately place your new cuttings in water. The longer you wait after cutting before putting the stem in the water, the more likely air will get in the stem. Air in the stem causes the clone to immediately droop and start dying. That’s why the new cutting must be put in water immediately (just like when cutting flowers or roses for a vase). Note: If using cloning gel or powdery, quickly dip the end of the stem first then place in water.
Some growers dip in gel first, then powder, then into the water.
Some growers trim the edges of their leaves, especially big leaves. This is because the cutting has trouble getting enough water to the leaves without any roots. That’s why it’s also a good idea to trim leaves if it’s very dry where you live (the leaves evaporate water quickly in dry air, and the plant can’t keep up). It can also help to raise the humidity or use a dome to keep more moisture in the air around clones. Trim the ends of leaves if they’re big, or if the air is dry (under 30% RH) where you live.