I am based in North London, it takes us about 2 hours to drive to Great Dixter or Sissinghurst, just to give you an idea of what to expect. The others who recommend these gardens are spot on, they are world famous, and can be combined in one day. There are various coach tour companies who visit them, which would save you from hiring a car. Here is one example, they visit those gardens every Saturday, and leave from central London.
No harm in hoping, and I certainly hope you are right. I do have my doubt, and an event like the Chelsea Flower Show takes many weeks to set up. Sadly I suspect it is unlikely to go ahead.
I still believe the economic impact is worse than the virus. We are now at level quarantine in our area. All large gatherings closed. Dallas just closed all resteraunts gyms schools churches. Even the bars😩😩😩
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