IMO They can take 30-32 degrees for a few hours..any more than that and the fan leaves can burn and the buds can turn to soggy spinach. It could get even worse if humidity is up. Other folks have stated that weed can withstand snow and after a snowfall the buds pop up through the snow and continue growing. I have never heard or seen that happen here in the high elevations of CO but maybe it happens other places.
Mulch the soil around your plants to keep the ground warm thus holding heat into the root ball. Straw or hay is great but use whatever you can find (lawn clippings, leaves, bark, pine needles, newspapers, old clothes, holey underwear, stained panties, grannys old bras, etc. haha.
If possible build a support structure (out of scrap sticks, 1x1 or 2x2 lumber) around your plants and cover them.with an old blanket and then drape a plastic tarp over them. The blanket/bed sheets will hold in the heat and the plastic will shield off moisture or rain, sleet etc. Any branches touching the blanket or tarp will freeze..so avoid that shit. :) Make sure if a wind kicks up it don't blow your shit all over the place. (bin' there dun' that)
Do not water later in the day as you want to keep that soil warm at night. Some folks say to water at night with warm water but I tend to think it may cause a short warming of the soil but later create an easier path for freezing (much like a Zamboni machine).
Don't rule out building a small fire next to them at Midnight or so. Or set up a little hibachi grill stove. Hang a thermometer off a branch and monitor temps.
You could take some cuts, pop them in water (or soil) and experiment with them. I have cloned successfully by sticking cuts directly in soil. I have no idea how they may do as far as seed production goes though. But ya won't know if ya don't try it.
One more thing: Do not rule out moving the plant. MJ is pretty damn resilient. I am assuming these are planted directly in the ground. I have had great success in digging up plants, popping them into 5 gallon pots and letting them finish indoors or in a warmer area. One was security breech issue and in the heat of the moment I literally grabbed the base of the stalk and ripped it out of the ground with the roots dangling all over the place. I quickly popped her into a 5 gallon bucket and in about a week she recovered. But mostly I dig then up with a shovel being super careful not to destroy the larger roots and gently place them in a bucket with the same soil that the plant was originally in.
Check your weather forecast and good luck amigo.
