Been playing this game almost 2 years and have no idea lol.

All of these sites will help you regarding backgrounds:

http://fairygarden.weebly.com/backgrounds.html
https://docs.google.com/presentation/d/1n1TuRE7lc3JK8wZeTe5mkrbqL_8LwkDcz_K7tlEQm1c/present#slide=id.p
http://www.freedomfairies.com/special-effects.html
http://www.alfflove.com/change-garden-background.html

The following information is from the Fairyland Guide thread (found in the Most Useful Topics section of the forum) - Post 29 & 30 -  Page 3

~ POST 29 ~
~ MAGICAL POT BACKGROUND EFFECTS ~

(A) – Automatic Effect
(SD) – Stardust Required Effect
(GD) – Gold Dust Required Effect
(S) – Seasonal Plant
(FG) Fully Grown
(RTH) – Ready To Harvest

Effects last for as long as stated.  Removal or harvesting of any plant required also removes the effect EVEN if has been Stardusted.

If you want to harvest the plant which has created the effect you need to use the Stardust Icon below your garden to freeze the effect for 1 week.

Wildlife can only be attracted/deterred if the plant remains in the garden, background effects alone DO NOT attract or deter any wildlife.

Pink Sky with Mini Pink Flowers (A)
Pot Required – Magical Pink Marshmallow
Plant required – FG Rosa Amora
Effect Lasts – Once RTH Pink sky disappears, mini flowers remain until harvested
Attracts – Piglet

Flying Pigs (SD)
Pot Required – Magical Pink Marshmallow
Plant required – RTH Rosa Amora
Effect Lasts – 1 week
Attracts – Nothing

Cloud (A)
Pot Required – Magical White Marshmallow Pot
Plant required – RTH Cumulus Albiflorus
Effect Lasts – 1week
Attracts – Kiwi

Heart Shaped Cloud (A)
Pot Required – Magical White Marshmallow Pot
Plant required – RTH Cumulus Amora
Effect Lasts – 1 week
Attracts – Kiwi

Grey Cloud (A)
Pot Required – Magical White Marshmallow Pot
Plant required – RTH Cumulus Albiflorus
Effect Lasts – 1 week
Attracts – Kiwi
Additional Items Required – Grey Garden Effect

Rain (A)
Pot Required – Clump of Grass
Plant required – RTH First Flower of Spring
Effect Lasts – 48 hrs - Spring Showers every 6 hours which last 1 hr
Attracts – Nothing
Additional Items Required – Cloud Effect from Magical White Marshmallow Pot

Rain and Rainbow (A)
Pot Required – Clump of Grass
Plant required – RTH First Flower of Spring
Effect Lasts – 48 hrs - Spring Showers every 6 hours which last 1 hr
Attracts – Nothing
Additional Items Required –
Cloud Effect from Magical White Marshmallow Pot

Butterpillaflora Rainbow (A)
Pot Required – Magical Rainbow Egg Cup
Plant required – Rainbow Butterpillaflora
Effect Lasts – While the Butterpillaflora is Sparkling
Attracts – Butterflies corresponding to the colour caterpillar nurtured on it. 50% will be Rainbow Butterflies

Red, Orange, Yellow, Green, Blue, Indigo or Violet Sky (A)
Pot Required – Magical Rainbow Egg Cup
Plant required – RTH Bellis Lycanea
Effect Lasts – 7 days
Attracts – Insect Liking Wildlife

Sun (A)
Pot Required – Magical Sundial
Plant required – RTH Solaris Igniflorus
Effect Lasts – 1 week
Attracts – Nothing

Moon and Night Sky (A)
Pot Required – Magical Sundial
Plant required – RTH Luna Serena
Effect Lasts – 1 week – Moon phase changes during the week.
Attracts – Badger, Hedgehog

Eclipse and Night Sky (A)
Pot Required – Magical Sundial
Plant required – RTH Luna Serena and RTH Solaris Igniflorus
Effect Lasts – 1 week
Attracts – Nothing

Shooting Stars (A)
Pot Required – Magical Star Pot
Plant Required RTH Stella Velleflora
Effect Lasts – 1 week
Attracts – Nothing

Desert Background (A)
Pot Required – Magical Tall Cactus Pot
Plant Required Any FG Cactus
Effect Lasts – 1 week
Attracts – Corresponding Cactus Wildlife

Grey Garden with Black Border (A)
Pot Required – Black/White Magical Pot
Plant required – RTH Tulipa Praecocia
Effect Lasts – 1 week
Attracts – Magpies

Aurora Borealis (A)
Pot Required – Magical Aurora Stones
Plant required – FG Piscis Aquabullae
Effect Lasts – While Piscis is FG
Attracts – Nothing (except Bluejay when planted with the other 3 FG plants required)

Moving Cloud (A)
Pot Required – Magical Old Boot
Plant required – RTH Ventus Quatriflorus
Effect Lasts – 7 Days
Attracts – Gazelle
Additional Items Required – Cloud Effect from Magical White Marshmallow Pot

Double Rainbow (A)
Pot Required – Magical Rainbow Eggshell
Plant required – FG Daffodil
Effect Lasts – 7 Days
Attracts – Easter Bunny

Blowing Fallen Leaves (A)
Item required – Completed Scarecrow with Scary Face (S)
Pot Required – Magical Old Boot
Plant required – RTH Ventus Quatriflorus
Effect Lasts – 7 Days
Attracts – Nothing

~ POST 30 ~
~ NON MAGICAL POTS BACKGROUND EFFECTS ~

(A) – Automatic Effect
(SD) – Stardust Required Effect
(GD) – Gold Dust Required Effect
(S) – Seasonal Plant
(FG) Fully Grown
(RTH) – Ready To Harvest

Effects last for as long as stated.  Removal or harvesting of any plant required also removes the effect EVEN if has been Stardusted.

If you want to harvest the plant which has created the effect you need to use the Stardust Icon below your garden to freeze the effect for 1 week.

Wildlife can only be attracted/deterred if the plant remains in the garden, background effects alone DO NOT attract or deter any wildlife.

Starry Night Sky (SD)
Pot Required – Any Zodiac Pot (free gift with any Zodiac Plant)
Plant required – Any RTH Zodiac Plant (S)
Effect Lasts – 1 week
Attracts – Zodiac Specific Wildlife

Jungle Garden (A)
Pot Required – Jewel Basket
Plant required – F/G Enchanted Forest Plant (Any)
Effect Lasts – Until it is RTH
Attracts – Hummingbird
Additional Items Required – The correct combination of FG Forest Plants and FG Enchanted Forest Plants

Pink Sky (A)
Pot Required – Pink Pot (free gift with Pink Ribbon Plant)
Plant required – FG Pink Ribbon Plant (S)
Effect Lasts – Effects lasts only while FG
Attracts – Flamingo when FG
 
Dark Sky with Flying Witches (A) and (SD)
Pot Required – Pumpkin (free gift with Halloween Plant)
Plant required – RTH Halloween Plant (S)
Effect Lasts – 7 days
Attracts – Halloween Seasonal Wildlife

Dark Sky with Web and Spider (A)
Pot Required – Any Pot (approx half of all pots will produce a left hand corner web, the other half a right hand corner web)
Plant required – RTH Trick or Treat Seed
Effect Lasts – 3 days
Attracts – Nothing

Dark Sky with Cats Eyes (A)
Pot Required – Any Pot
Plant required – RTH Trick or Treat Seed
Effect Lasts – 3 days
Attracts – Nothing

Dark Sky with Flying Ghosts (A)
Pot Required – Any Pot
Plant required – RTH Trick or Treat Seed
Effect Lasts – 3 days
Attracts – Nothing

Flying Peace Doves (SD)
Pot Required – Clump of Grass (free gift with Poppy Plant)
Plant required – RTH Poppy Plant (S)
Effect Lasts – 1 week
Attracts – Peace Doves

Snow On The Ground (A)
Pot Required – Christmas Tree or Ice Cube Pot (free gifts with Chritstmas Tree and Ice Flower)
Plant required – RTH Christmas Tree or Iceflower (S)
Effect Lasts – Until the last Christmas Tree or Iceflower is harvested
Attracts – Winter Seasonal Wildlife

Falling Snow (A) and (SD)
Pot Required – Christmas Tree or Ice Cube Pots(free gifts with Christmas Tree and Iceflower)
Plant required – FG Christmas Tree or FG Iceflower (S)
Effect Lasts – Until Ready To Harvest
Attracts – Winter Seasonal Wildlife

Falling Snow and Pine Trees (SD)
Pot Required – Ice Cube
Plant required – RTH Iceflower (S)
Effect Lasts – 1 week
Attracts – Winter Seasonal Wildlife

Flying Santa (SD)
Pot Required – Christmas Tree Pot
Plant required – RTH Christmas Tree (S)
Effect Lasts – 1 week
Attracts – Winter Seasonal Wildlife

Purple Sky with Fireworks (A)
Pot Required – Champagne Flute (free gift with New Years Eve Plant)
Plant Required – New Years Eve Plant (S)
Effect Lasts – 48 hours
Attracts – Nothing

Mini Shamrock Carpet (A)
Pot Required – Leprechaun Hat
Plant required – FG Four Leaf Shamrock
Effect Lasts – While Shamrock is FG
Attracts – Leprechaun

Shamrock Rainbow (A)
Pot Required – Leprechaun Hat
Plant required – RTH Four Leaf Shamrock
Effect Lasts – TBC
Attracts – Nothing

Dark Garden (GD)
Pot Required – Earth Pot (free gift with Earth Flower)
Plant required – FG or RTH Earth Flower (S)
Effect Lasts – 1 hour
Attracts – Nothing

Fallen Leaves (A)
Item required – Completed Scarecrow with Scary Face (S)
Effect Lasts – as long as the Scarecrow is in the garden
Attracts – Nothing

so you need stardust

Most of the backgrounds will stay for 7 days when first activated, but after that you will need stardust to keep them for a longer period of time. Each time you stardust, you get an extra 7 days.

You can keep on replanting to get those effects, without using stardust.

The scarecrow gives autumn leaves whenever in the garden.

thanks ladies