Prize-winning crossword

Use the following answers to complete this anonymous gardening saying: ‘13 across 12 across 31 across 9 across 5 down 25 across should 36 down to 9 across a garden 20 across’.

ACROSS

3 Substance added to soil to make it more productive (10) 9 Law, regulation (4) 10 Last le er of the Greek alphabet (5) 12 See 5 down 13 No person in particular (7) 16 Engrave with acid (4) 18 Weapons (4) 20 Earliest (5) 22 Type of rose, and whisky (7) 23 Large oval brown seed of a tropical palm (7) 25 The Earth, its countries and peoples (5) 26 Crack, split (4) 28 Social climber (4) 31 and 34 12 across ___

Millionaire?, TV quiz snow (5,2,2,1) 35 Coloured part of a flower (5) 37 Decomposed vegetable ma er used as a soil conditioner (4) 38 One who raises plants commercially (10)

DOWN

1 Locality, region (4) 2 Stiff, sticky soil (4) 4 Wear away by the action of wind or water (5) 5 and 12 across Group who had a 1967 hit with Pictures of Lily (3,3) 6 Flat, thin plant structure (4) 7 One who plants seeds (5) 8 Underground parts of a plant (5) 11 Traditional story (4) 14 Capital of Kenya (7) 15 Plant of the polygonum genus, with twisted 8 down (7) 17 26 down ___, famous outlaw (4) 18 Heathrow, for example (7) 19 Illuminated at night? (7) 21 Unopened flowers (4) 24 US state, capital Des Moines (4) 26 Red-breasted bird (5) 27 Special aptitude or ability (5) 29 Lightweight wood used in model making (5) 30 Duelling sword (4) 32 Garden outbuilding (4) 33 Porridge ingredient (4) 36 Rugby score (3)