If you are taking cuttings from a lilac the best thing to do is rooting hormone on the stems and put them in seed starting mix and place in a bag to contain moisture. This is what I do for lilac cuttings and have had great success. Hope it helps.

If you're keeping them under an over-turned tub most of the time, this may slow down the rooting process considerably. Plants need light to keep the leaves alive and supply the plant with energy. So a clear plastic cover is better.

It's a translucent tub. The kind you get at Walmart for about $4.

It's been consistently 100 degrees here, so I decided to bring the box inside. It might have been too hot for cuttings, especially inside the overturned tub. I'm now lighting it with the top for a 50 gallon fish tank. I had great success growing grass (just regular grass -- I was making my own grass plugs) with it a while back, so I know it puts out enough light for plants. Hopefully this turns my luck around. I still have some cuttings that haven't wilted, drooped, or rotted, so we'll see.

What type of material did you take? Size, maturity? If you are able to dig a sucker, they can often be severed and brought up with some roots, allowing you to start with a much larger specimen without the initial hurdle of root formation.

At this point, adding a bit of root hormone to water (when watering is necessary,) could help.

Your cover sounds like it would be much too hot, like being inside a parked car with the windows up. Try cuttings in dappled light if possible.

Sand isn't an ideal medium for this, do you have somewhere in the ground where you could have a nursery? If not, perlite might work better. What about just putting them where you want them to be in the ground? No future disturbance necessary. If too sunny, some type of temporary shade (that doesn't block air flow or hold heat) can help. Maybe a lawn chair if you don't mind it being out of place for a couple weeks.

Should be enough natural humidity outside. Mist shouldn't be necessary, and could cause fungus or other diseases to thrive on the foliage. I would prefer air flow, the nemesis of fungi and many other nasty pathogens.

Well, the lesson I've learned from this little experiment is that rooting cuttings is not easy. I guess I should qualify that by saying rooting lilac cuttings is not easy.

I thought it was too hot outside and I was trapping too much water, causing rot. So I brought them inside and stopped using the dome. Their condition got much worse and now it looks like the huge majority or even all of them will die.

Try outside in the shade, dappled under a tree is ideal, where it would likely happen naturally. Semi-hardwood, or the suckers I mentioned. Without the dome or direct sun, the temperate won't rise above ambient temp.

Sometimes when propagating, the entire cutting can look dead but new growth can come from roots that have formed under the surface. Many times I've pulled what I thought were dead twigs, only to realize I've just destroyed a new baby plant that would have emerged from the surface in another week or two. I've planted many lilacs when I lived in OH, all were from cuttings and suckers.

Sending good vibes!!

Yeah, I got 2 suckers, which are both doing well and showing new growth. But I wanted to try out cuttings for fun.

Well, one of my two hydrangea cuttings rooted. The other one looks perfectly healthy, but I see no new growth yet.

Most lilacs look dead. There are 3 or 4 of the 21 which still have green leaves and upright stems, so not all hope is lost I guess.

The hydrangea cuttings were in the same bin as the lilacs and were added one week after the lilacs. That means this one rooted in 2 weeks.

So I can confirm what you all probably already know: hydrangea is a lot easier to root than lilac.

Not on this forum too much but just wanted to say your method should have been ok. I think you jumped the gun though and should have let them be at least two or three more weeks since lilac do take time. Did you use rooting hormone?
I've done shrub cuttings in sand many times with good luck, under a tub and under baggies and under nothing but shade cloth.... Just be patient, some shrubs take months to root..... Give it another try, what have you got to lose? Try some more hydrangea or boxwood, they should be easy confidence builders! :)

Im also rooting lilac cuttings for the first time. Some are rotting on the bottom but most have a really nice callus formed, its been 1 month now. I got clear plastic storage containers from walmart. 3 of them all the same size, I put a heating pad under the bottom one and 1 inch of water in it. I set another one inside the bottom one with 50/50 peat moss and sand mixture, wetted to slightly damp but not wet with rain water. Over the top I put the 3rd container upside down to make a dome, drilled small holes in the 4 corners and put roofing nails through them to hold the cover in place. Set in an area in my house that gets about an hour of direct sunlight a day, when the sun passes that window. Heating pad is always on, keeping temp of rooting medium at about 78 degrees. I didnt do any misting, and remove the cover very rarely. Used liquid rooting hormone, same as dip-n-grow but off brand. Powders work like crap in my experience. Another week and I hope to have good root growth, not sure why some cuttings rotted when others callused great, maybe hormone was mixed to strong, I diluted it 12 to 1.

Yeah, all my deaths are due to rotting as well. Surprising because I am using straight sand and a very coarse sand at that. I'm shocked how well this sand holds water. I think my biggest mistake was that when my box was outside, I was misting with the hose and I think that was wetting the sand too much. Now that it's inside I am misting with a spray bottle and the sand is a lot less wet and compacted.