If seasons would be limited to the graphical effects, a few new items and some new interactions, it wouldn't really be a complete expansion pack. A popular feature from Unleashed (The Sims 1) has been brought to the Sims 2: Gardening. Sims can grow and harvest some fruit and crops, and use it to cook dinner with. There are six types of plants: tomatoes, eggplants, pole beans, strawberries, cucumber and peppers. You can sell the harvested crops in a home business, or put them in your home-cooked meal to improve its hunger satisfaction.
To start growing plants you'll first need to reserve some ground for it. The tool to plot down this dirt works similar to that of foundations: you drag an area which lights up, and if it's valid then it'll put down the dirt. Removing it again can be done by simply holding the Control key while doing the same. Once you made the area you like, start planting whatever you like - either one by one, or a simple "Plant many" to do it all in one go.
You won't be able to have all the plants from the start though. The badges introduced in Open for Business make a return, in the form of new gardening and fishing (more about that later) badges. Planting, watering and tending plants will increase your gardening skills and eventually get you that golden badge you need to get all plants available. There are also some orchard trees which need less attention, but only grow fruit (apple, orange or lemon) in some seasons.
Although becoming a good gardener takes practice, and the yield value increases when you get the badges, you do get some help from the game. You don't need to take a wild guess which plants need tending and which don't: when you hover the cursor over a plant or tree, you'll see how well it's doing. Of course there are also the graphical effects showing the growth etc. To help you out more, there are "Tend many" and "Water many" interactions. Use those, and your Sim will go by all plants tending or watering them without you having to click each single plant.
There's more to do in the garden though. Trees will drop their leafs in the fall, which is useful garbage. Only if you have a compost bin though. Have your Sim pick up the leafs, put them in the bin, and the garbage will start composting. After a while you can use the compost as fertilizer for your plants. As anybody should know, a more fertile ground grows better plants.
There are many more tools to help you tend to your vegetables. A big one is a greenhouse. You can build it any size you like, and put your little plants in there. That way they are shed from very very bad things like insects, weather effects and the like. The "Garden Schpritzers", which cover an area around them in either 90, 180 or 360 degrees will keep your loved ones watered, and the ladybug box will keep bugs away (in the right seasons).
If you like you can also call the gardening club, which will send over one of their members as soon as you do. You can buy their pesticide for your green spots under attack. You can also try to join them, which gives you some special advantages. Your garden may be awarded for being the nicest in the area and you get discounts on certain necessities for your garden. You need to spend enough time in your garden making it look nice enough to be allowed to join the exclusive club.
Another way of getting some easy food is by fishing in a small lake. Those lakes are no longer useless decoration: besides being able to put a new "Flowy Floater" fountain in a lake, your Sims are also able to get some fish from the pond. There are several lures, each for a different kind of fish (bass, catfish and trout). Just like the plants, fish can be used to cook or sell. You can also get out the barbecue and prepare it on that.
Fishing is not available through the entire year. Fishing during the winter may be a little hard, and your Sims won't make a hole in the ice and fish through there. Just like with gardening there's a special fishing badge, which will give your more options for lures. And as each lure attracts a different kind of fish, you'll be able to catch more sorts of fish when you've practiced a bit.