If there's one plant you need in your garden, it's marigolds.
These hardy annuals bloom in spite of hot, dry weather - the pot marigolds even open and close with the sun.
In addition to being very easy to start from seeds, marigold roots exude thiophenes, which kill nematodes. They're also a natural pest repellent and for years have been planted around garden borders.
Once you buy old-fashioned marigolds, you can save seeds and re-plant the following year and still have enough to share!