Cruise from Kew Gardens to Westminster - how scenic?

Depends on what you're idea of "scenic" is. You'll be going through leafy suburbia, then a bit more of an ex-industrial region, and finally coming past Tate Britain and Millbank. It's a nice flavour of the different types of London, but there are few huge sights on that side of Westminster.

Sounds interesting, but not necessarily scenic for much of the journey.

We just did this a day or two ago....Phillip's description is apt. Not particularly scenic at all but a change of pace from tube and bus. The captain gave us a short, funny safety speech when we boarded joking about on board toilet/slop buckets, life jackets, etc. When he announced ten minutes later that the upper deck folks needed to move out so they could dismantle the wheelhouse to get under Hammersmith Bridge, everyone chuckeled and sat still. No joke, he said, and indeed later heard that in another ten minutes we would have sat for 1 1/2 hours waiting for the tide. Kew is huge, we spent many hours walking. Consider the shuttle as a possible alternative. The gigantic Temperate glasshouse is closed for renovation. PS. The Creepers and Climbers is not a botanical display of exotic vines...it's a playground. Our "duh" moment.

Denny, about how many hours did you spend at Kew? Are the plants from Temperate House still on display somewhere or out of view?

Gardens are a big deal for me, and we spent 6 hours and saw about 3/4s perhaps of the grounds. Much is arboretum as well. Liked the Kew Palace and adjoining herb garden a lot. I have no idea about the Temperate House plants; saw nothing indicating anything other than closed. I was disappointed myself, but t there's plenty enough to see. There are several choices for snacks and meals and ice creams so easy to spend as long as you like. We got the boat information/schedules from the information desk inside the area near the Victoria Gate, main entrance. We left through the Elizabeth Gate to walk about 15 mins to the boat. It was our first visit in 3 trips to London and very happy we went. Had been to RHS Chelsea the day before, and that is something to behold.

We tried last May but missed the timing (we tubed back and caught the afternoon service at Saint Paul's - win some, lose some.)
My in-laws did take it when they went in August and my MIL raved about it.

Question: How big of a Pink Floyd fan are you? Going past Battersea station, I almost wanted to see a pig go floating by.

Many of the plants in the Temperate House are very large. Not only would it be impossible to move them, there is no alternate building in which to house them.

I had read that all but the very largest plants would be moved, but could find no reference as to where they were being moved. Just found some more info. This reference doesn't say specifically, but seems these plants are not on view: "The horticultural team has been working since 2013 to move the entire plant species collection from the Temperate House to the newly created Decant Nursery (previously the Munchbox),where it is being propagated. Very large plants have been lifted, potted and transported to the Decant Nursery spaces. Additionally, a new purpose-built Propagation House (which will be a permanent legacy of the project) is providing glasshouse nursery space for continued care of the main collections and space for growing the changing annual displays. The new internal landscaping will generate regional zones for the new plants. Following the successful propagation period there will be a mix of mature and young plants by 2018."