Garden numbers dropped from a high point of 42 in 2016 to 21 this year, though there was only one fewer show garden with eight on display, including Andrew Fisher Tomlin's Blind Veterans and Paul Hervey-Brookes' Viking Cruises-sponsored garden.
Brexit and generally economic and political uncertainty was cited as the reason. The RHS hopes 140,000 people will attend the 4-9 July event.
Andy Sturgeon's garden, overseen by David Dodd from the Outdoor Room, brought together 25 apprentices to join together parts of previous well-known show gardens by top designers, all done with just five weeks notice.
An APL garden feature was alongside Sturgeon's 'Watch This Space' garden and TV's The Hairy Bikers broadcast live from the show's RHS Kitchen Garden designed by Juliet Sargeant on BBC1, while Gardeners' World is also broadcasting full coverage.
Conceptual garden numbers fell from 9 to 3, and the RHS dropped water, city, Capability Brown and summer garden categories.
A new Changing World category had six gardens including a Landform/Squire's Garden Centre/London Stone collaboration designed by Rhiannon Williams and a Perennial-sponsored Sanctuary Garden design by Tom Massey, symbolising a professional horticulturalist's journey from chaos to safety.
Streetscape had a Hold back the Flood garden designed by Will Williams and St Modwen sponsored Martyn Wilson's Brownfield-Metamorphosis urban regeneration garden.
Dodd said the garden numbers continued what happened at Chelsea in May where show garden numbers halved. He said: "People blame Brexit and panic over the economy but we've had recession and good and bad times and 2018 is meant to be very good".
The apprentices who built the garden came from companies including Frogheath and Burnham Landscapes.
Landform's Mark Gregory said Hampton had a lot of quality but was a "bit light" on garden numbers, which he felt was a sign of the times. The Landform-built climate change-themed Urban Rain Garden was a joint effort with London Stone and Squire's - "a different way of pooling resources", splitting sponsorship to save money, which Gregory said could be a way forward for garden shows: "Multiple people involved is the right thing to do, to spread the burden."
He said: "What I'd sooner see is lots of smaller people [exhibiting gardens at shows] with a little bit of money bringing more content rather than big names and budgets." He added that more overseas visitors, designers and sponsors would also be welcome and that the hung Parliament had created uncertainty in the UK market, with some developments on hold, and the market having peaked last year.
Plants are supplied by Hortus Loci and furniture is from Barlow Tyrie and available from Squire's.
Coblands/Glendale's Lewis Normand said he supplied plants to Paul Hervey-Brookes at Hampton and Chatsworth and Claudia de Yong/Wyevale Garden Centres at BBC Gardener's World Live and says more UK growers are supplying shows because of exchange rates.
Blind Veteran's UK designer Andrew Fisher Tomlin said giving money to younger designers to enter was proving an incentive for the Ascot Garden Show he is promoting for 2018. He says there are plenty of desigenrs wanting to exhibit, but a lack of sponsorship out there. Landform won the best construction prize for building the garden. Fisher Tomlin said he chose Hampton for the garden because the public would be able to access the walk-through better among other reasons. The Countess of Wessex launched the garden.
Master Grower 2017 is Penberth Plants, which is among 100 nurseries in the floral marquee, with 20 growers outside in the Plant Village. Growers said they were in a dilemma about whether to exhibit at BBC Gardeners' World Live or RHS Chatsworth in 2019, which will be on the same date for the first time.
The best exhibit in the Floral Marquee went to orchid specialists Vacherot & Lacoufle, while Marshalls Malmaisons was awarded best Plant Heritage exhibit for their heritage carnations display. In addition, David Austin Roses took the title for best rose exhibit, Hooksgreen Herbs won best Cook & Grow exhibit and the New Design Award was presented to Fernatix.
- Edible flowers: Borage, viola - a new range from Franchi, who say agretti is the big new vegetable to grow.
- Seaweed: Mr Fothergill's has licensed the Australian Seasol range to sell at Homebase/Bunnings from August and at garden centres from January 2018.
- British roses: Rose of the year was bred by Northern Ireland's Dickson's, with 2019's rose of the year from Harkness of Hertfordshire. Fryer's also launched two roses at the show.
- Low budget or collaborative garden builds. Southend's garden cost £1,000 and APL's garden cost £3,500. Landform, London Stone and Squire's joined forces for their garden. Andy Sturgeon's garden had help from apprentices.
- Edible gardening and more TV coverage: The Hairy Bikers Kitchen Garden Live and Saturday Kitchen are both broadcasting from the show's edible garden, while there is also a Cook & Grow marquee with growers such as Blackmoor, Hooksgreen Herbs, Pennard, Franchi, The Garlic Farm and Battlesbridge Mills Garden Centre. Andrew Fisher Tomlin's Blind Veteran's UK: It's All About Community garden includes a Jon Wheatley edible garden. Gardeners' World also has three shows covering the event.
- Mental health and autism gardens from Franchi/Easi Works, Zoflora and the Centre for Mental Health.
- Flooding and climate change gardens from Landform/London Stone/Squires and Streetscape.
- Children's garden features including a Butterfly Dome, soft play, Zoflora Children's Wild Garden (which won best in show) and various talks and activities. Fiddlehead fairy gardens from Perennial.