While plant cuttings are an amazing way to take a shortcut when gardening, taking care of them properly so they root and thrive is another story. I’ve had a lot of trouble with this in the past, but have worked out the kinks – so here’s how to do it!
Once you’ve made your cuttings, planted them, and watered them, they need to go under lighting. I like to use a 4′ T5 fluorescent light setup so I can control how much light they get and for how long, but you can also grow outdoors if you like – it’ll just be less consistent.
To make sure your cuttings will root properly, you need to control the temperature in the bottom of your container. Most cuttings need a temperature of around 71°F (21°C).
It’s important to get root temperature right.
Keeping your cuttings in a colder area will dramatically slow root development. If you’re having trouble finding a spot that’s warm enough, you may need to supplement your cutting trays with a seedling heat mat.
If your root area is too hot, your cuttings will be encouraged to produce vegetative growth instead of root growth – the opposite of what we want.​
Keep the humidity level higher than normal when caring for cuttings to prevent water loss from leaves, but take care not to go too high. If you’re using a humidity dome, either get one that has a vent at the top or make sure you remove the dome once or twice a day to avoid spiking your humidity level too high.
Another issue with humidity domes are their tendency to increase the air temperature, especially when growing under lights. This is another good reason get a dome with a vent, or at least use a thermometer of some kind to monitor air temp. I’ve found the adhesive thermometers used in beer brewing to be useful here.
An example of damping off
This artificial environment of dome, lighting, and humidity shouldn’t last for long. The sooner you can get your cuttings into a more normal environment with air flow and no dome, the better off they’ll be.
After about a week, remove the dome and monitor your cuttings to see if they begin to wilt. If they do, they’re not ready to go dome-less, so try again in 1-2 days. If they still start to wilt, they might be suffering from damping off, a disease that strikes in high temps and high humidity.
How to Feed and Water Your Cuttings
When you’re planting your cuttings, you need to water them well…and not just with water. Ideally, use water and a rooting hormone . It will seal the cut stem, but also stimulate the production of new root cells much quicker than water alone.
As far as what growing medium to use, stick with ones that drain well, like hydroton or perlite. If you use a medium that doesn’t drain well, you risk root rot due to too much water.
Aside from the root hormone you use when planting, don’t bother fertilizing your cuttings. It’s counterintuitive, but fertilizing them can actually slow down the process. Think about it – you’re providing a steady stream of nutrition directly to the plant’s stem…why would it be incentivized to grow new roots? Once your cuttings start to develop tiny root hairs, you can begin to lightly mix in a flowering fertilizer. You choose a flowering fertilizer for bigger root production vs. vegetative growth production.
After your cuttings have rooted and are starting to produce new vegetative growth, you can begin to lower your lights closer to the top of the foliage. Be aggressive here – if you’re using a fluorescent, you can get as close as 3″ to the top of your plants without damaging them in any way.
How to Light Your Cuttings
When your cuttings are rooting, you should keep light on them for at least 18 hours a day. You can go up to a full 24 hours a day if you wish – they won’t suffer for it.
Once they’ve begun to root, cut lighting back down to 18 hours a day and make sure they get a solid six hours of night time.
Using Pesticides and Fungicides on Cuttings
As long as you are taking your cuttings from healthy plants that are completely free of diseases, fungus, or pests, you shouldn’t need to use any pesticides or fungicides. However, as they begin to root and especially if your humidity is high, you may want to spray a bit of No Damp as a foliar application to prevent damping off.
As far as insects, your two biggest problems will likely be fungus gnats and spider mites. They will destroy every cutting if given the chance and set your propagation efforts back weeks.​
To treat spider mites, ​your best option is to either make a homemade insecticidal soap or use something like Safer Brand’s insecticidal spray. It’s safe to apply to plants that you will consume and works quite well against spider mites. Make sure to spray the underside of your leaves as well to get full coverage.
Fungus gnats require a different approach. They lay eggs in your growing media. Once hatched, the larva will attack the new roots and root hairs, leeching them of nutrition. The best way to figure out if you have fungus gnats are to use sticky cards as a precautionary measure.