In Lienea live Aunt Maggie who have a small field in the center of the village. If you have a seed (most likely one Pom Seed) in your Inventory, then Aunt Maggie will offer you to raise it. You need to pay 2,000 Gald for raising it. After you give her the money you have to choose which fertilizer will be used first. There are for different fertilizer:
Red Super Gro
Blue Kwik Gro
Yellow Miracle Gro
White Sure Gro
After you choose one, then Aunt Maggie will tell you to wait for it to grow. Leave the village and come back immediately. You will now see a small bud growing in her field. Talk to Aunt Maggie again to choose another fertilizer for 1,000 Gald. Reenter to see the seed to grow bigger. Talk again with Aunt Maggie for another fertilizer for 1,000 Gald. Reenter the village again to grab to fully blossomed Plant for a Treasure. What you get depends on which fertilizer you gave her.
If you want to grow Miracle Gel from a Pom Seed, then you need to choose White Sure Gro, Blue Kwik Gro and White Sure Gro (4, 2, 4). Some Seeds have very good Treasures to grow, but the game can be very expensive. If you want to grab 15 Terra from Charak Seeds, then you need to spend around 330,000 Gald. You have to buy Lanakear Seeds for 150,000 Gald (10,000 Gald each piece) in Seed Shop first, then plant Lanakear Seeds to grow Phen Seeds first and then plant Phen Seeds to finally grow Charak Seeds. After that plant Charak Seeds to get 15 Terra...
Most Items can be gotten by normal means, but there are some Treasures that are not obtainable otherwise. That would be Sour Milks and Liqueur Bottles which cannot be bought in Shops. At the begin of the Game Miracle Gels and Antidote Charms might be also a good option to get. Antidote Charms cost 10,000 Gald in Shop, but here you can grow one for only 4,000 Gald plus cost for one Pom Seed.
Mandrake in Fitzgald (in which Lienea and Neuestadt are), Alra and Baneshroom in Cloudius will drop Pom Seeds. You can also buy one for 50 Gald in Darilsheid Castle from Otto in his Labor. Later in the Game the Pom Seeds are also sold for 1,000 Gald in Seed Shop.
Estima Seeds can be stealed from Alra in Cloudius in the middle of game otherwise you have to wait until later until you've got the flying Draconis so you can go buying Estima Seeds in Seed Shop for 10,000 Gald a piece. Estima Seeds can be used to get 15 Barracudas and Cods (unless you got it all from Warfish in Terazzi Castle). The other worthwile items are Dolgenia Seeds and Lanakear Seeds from which you can get more items. Charm Bottles may be also interesting if you don't plan to get it from Mach Boy Race.
If you've already got 15 Flare Bottle from Berserker on the Pirate Ships, then you can ignore it and concentrate on getting 15 Phen Seed so you can get Charak or Oriola Seeds and thus getting the best items.
The best reward would be of course Cutie Mitten of which only one exemplar in Dycroft exist. If you're a collector, then you should also get Bonito Flakes and Squid Jerky which are rare too. Softy Kreem might be interesting too if you want to collect 15 Winner which can only be done here since the Seller in Neuestadt would trade any of your Winner against new Softy Kreem.
Don't bother to get Bellebane, Lavender, Savory since there are easier and cheaper way to get unlimited amout of it. You can also get unlimited Elven Cape for free in Tower of Druaga.
Charak Seed grow the best stuff of all Seeds. You should get at last one Golden Seed to trade for the Giant in Darilsheid which in turn is needed to get the last Sacred Skill "Phoenix" for Stahn Aileron. You should also get some Terras.