I'm going to go out on a limb here and tell you right off to find yourself some Maelstrom Snap Dragon seeds. While Burning Snap Dragons will probably get you more water lily faster Maelstrom Snap Dragons are practically your one stop gardening choice for Grizzleheim and Celestia clothing for Fire wizards.
Water Lily comes up quite a lot and can be hard to find out in the spiral floating among the Cat Tails. You can get Water Lily from Burning Snap Dragons, Maelstrom Snap Dragons, Ultra Helephant Ears, Ultra Huckleberries, and Ultra Ninja Figs. I've been having difficulty finding the Ultra seeds so really have no personal confirmation or information on those. I can tell you that I have grown 10 Burning Snap Dragons for 30 days so far and received 7 Water Lilies for my efforts. Growing Maelstrom Snap Dragons for 30 days only gave me 1 Water Lily BUT I also received 21 Perfect Ruby, which Dezzy also mentioned was used in the Fire Sudrilund Set of clothing. Both plants require large plots. You can easily fit 12 large plots into a large area ... you CAN fit more than 12 but then you really need to be careful with placement of your gardening spells or you'll end up missing one or two plants. I really hate when that happens. Anyhow, personally, I would plant 5 Burning Snap Dragons and 7 Maelstrom Snap Dragon. Hopefully the Burning Snap Dragons will also provide you with some more Maelstrom Snap Dragon seeds for the next cycle of gardening.
Maelstrom Snap Dragons are the only plants currently available that produce Kelp. The Giving Tree is also reported to give Kelp but how many people have those hanging around? After growing 10 Maelstrom Snap Dragons for 30 days I found myself with 4 Kelp in my possession. Patience will definitely be required here, I'm afraid.
You'll never guess which plants can give you Shell? Yup! Maelstrom Snap Dragons. Also Fickle Pickles and The Giving Tree is rumored to drop Shell. When I grew 10 Maelstrom Snap Dragons for 30 days I received 6 Shell while the same amount of seeds and time spent growing Fickle Pickles produced 4 Shell.
Aquamarine & Spring
Dezzy also mentioned Aquamarine and Spring as possible ingredients for the Fire wizard's Celestia gear. I've covered Aquamarine many times because it comes up so much. Normally I recommend growing King Parsley for Aquamarine - it will give you Spring too. 10 King Parsley seeds grown for 30 days produced 9 Spring and 10 Aquamarine. I managed to reap 29 Spring and 21 Aquamarine from Ultra King Parsley plants, Fickle Pickles gave me 1 Spring and 5 Aquamarine.
However, Maelstrom Snap Dragons also can give you Aquamarine - I told you, practically one stop growing - the only reagent on this week's list that you can't get from Maelstrom Snap Dragons is the Spring. You know what produces the best amount of Spring though? Pink Dandelions. 10 Pink Dandelions delivered 38 Springs in 30 days and they are a small plot so you can easily fit a couple small plots in with your 12 large plots and still be able to use the large area gardening spells with ease.
Did I mention that Maelstrom Snap Dragons can also produce a variety of Ultra Pet Snacks at Elder harvest? Yeahh, I'm definitely on Team Maelstrom for this week's list of reagents.