Answer: It is always hard to leave a garden behind, so it is worth a try. There is one caution however and this is if the property has been sold you might not be allowed to take the plants so that is something to check into if it applies here.
Generally, the "long term storage" refers to storing bulbs when they are dormant. If they are in full growth, in my experience you would be more likely to have success by potting them up, keeping as much of a rootball as possible.
Cannas may be huge underground, so you may have to try to take a division as best you can. Cannas are heavy feeders and like plenty of water, especially so in pots.
The amaryllis bulbs should be potted at the same depth as they are growing, if at all possible, and replanted into a soil similar to the one you are digging them from, if possible.
Creeping thyme and mint can also be dug and moved as "sods". Mint will do very well in a pot.
The Russian sage is very deep rooted and hard to transplant, but you should be able to take cuttings from it. The sage and many others (thyme, tarragon, mint, horehound) will also do well with tip cuttings. Tip cuttings taken in early summer are usually best, but you may be successful in May. They can be rooted in soilless mix using gentle bottom heat.
If you try to divide or transplant, water them well the day before you dig, and take as much root as possible. Trim abck the tops to compensate for root loss. Plants dug from the garden never seem to fit into pots, so you could use damp newspaper to wrap the rootballs and then set them in short plastic bags so that the roots are in the bag and the tops are open to the air. This should help keep them moist for several days if need be. Protect the rootballs from heat and drying out. Replant immediately or within a few days if at all possible.
Finally, if you think the plants will need to be out of the ground for a longer time, you might try digging and potting them very early in the season so they have some time to adjust to those conditions as they kick into growth for the season. This also gives you more leeway for your replanting schedule. Once you replant, treat them as you would any newly planted plants with plenty of water until they are reestablished.
Good luck with the move!
Q&A Library Searching Tips