Sorbaria sorbifolia I believe.

A rambler rose - I can't name the variety but it could be Rambling Rosie.

Ok.....Where do we start. This is a no no....."I've already repotted them in more loose, drier soil. Water only once a week". You never water a cutting to root. All you do is let them harden off at the cut part, or callous over. Then dip in rooting with fungicide hormone and stick it in just MOIST soil, not WET. You never water a cutting until it is growing leaves. How is your cutting going to benefit from a good drink of water, when there is no leaves to take up anything. The cuttings just sit in that wet soil, and rot. These cutting will not take up water until they are in leaf. What causes the roots to grow is HEAT not water. The more heat the better. I have a friend who lives in Florida, and when he cuts his plumies up, he tosses the cuttings into a dirt pile and they just root in full sun, with no water. Keep your cutting close to a strong grow light, in a sunny warm window, preferrabll in a black pot that the sun will warm up, or put heat matts under them. They will grow roots with no water. The whites spots, I am not sure of what they are unless you send a picture. Could be anything. If it is mold, I would buy a mold control spray you can buy at the local greenhouse and treat your stems. Don't give up on them!!! If you think that the bottom of your cuttings have the slightest bit of rot, cut them and follow the first step I told you ok. If the cuttings are long enough, you can salvage them and start over. When you get a first leaf, or if your cuttings start to really shrivel because your soil is dry , lets us know and from there we will tell you what to do with the watering. Just worry about one thing at a time ok. It can be a rewarding experience to see these plumies root if you just leave the water out and give lots of heat. Remember...HEAT makes roots, not water. When you get roots and leaves, then, water makes it grow..:-) Also YES, use the fastest draining soil you can make..Good point!

Cymbopogon citratus (Lemongrass) is a tropical and would be unlikely to survive the winter outside without considerable protection. It should be grown as a houseplant until the chance of frost has passed in the spring. Cortaderia selloana 'Rosea' (Pink Pampas Grass) is hardy at least through zone 7. It should be planted outside when it arrives. I would plant it in well draining soil. If you have clay, you might consider making a small berm to aid drainage.