6 Secrets to Successful Sims 3 Gardening
1. Skillz
There are two skills you need to be a great gardener: gardening (duh) and fishing. If your Sims are busy, you can have another household member actually catch the fish. Then just drag them into your gardening Sim's inventory.
These fish can then be used to fertilize your garden. They make a HUGE difference. Fertilized plants grow faster, yield more produce, and give produce of a better quality. The better the quality of the fish used as fertilizer, the better your results.
(Although you definitely get a situation of diminishing returns, so don't get too caught up on the quality of the fertilizer.)
2. Auto-Water
Watering is boring, right? And gardening takes so much time, why not take that task off your Sim's to-do list? A Sim with level 7 Handiness skill or above can upgrade the lawn sprinklers to "water automatically." Automatic sprinklers are awesome, and definitely cut down on the rate of accidental plant mortality.
Just be sure to position your sprinklers away from sidewalks or your house. They will cause annoying puddles to form on any surface that isn't grass and soil. And watch out for the corners - I find that it's easy to accidentally plant something in a spot that happens to be just outside the sprinkler's reach.
3. Garden Every Day
Basically if you want to grow more than two or three plants, you can't have a day job. Your Sim can probably eke out a meager living with a home-based business like writing or painting, but a proper career is out of the question.
Gardening takes a TON of time. I estimate it takes about an hour of in-game time every day, for every four plants. And that's if you are able to upgrade the sprinkler to auto-water! If you have to manually water the plants, your garden will take a lot longer.
4. Not The Path To Riches
Even though you can sell your produce, you're not going to make a living at it. I haven't broken down the numbers, but from strictly a perspective of hourly work versus wage, gardening is one of the worst. On the up side, you can eat your garden produce, which takes care of a lot of any household's budget.
Financially speaking, your best bet is to both garden AND do something else (like Inventing), or to have a spouse who can bring home the Simoleons.
5. No Walls
In Sims 2 you could build cool greenhouses. In Sims 3, the only thing you can put around your patch of earth is fencing. If you try to build walls around a garden, it won't work.
If you don't want to just plunk your seeds in the lawn, you can change it to soil. Use the Terrain Paints in Build Mode to make your garden look more garden-y!
6. Can't Plant A Seed?
There are many seeds that you can only plant after your skills are high enough. If you find you can't plant a seed, this is probably the case.
If you click on the grayed-out "Plant" menu option, you should get a little tooltip with an explanation.