Keep Seedbeds and Transplants Moist
Newly planted seeds need frequent watering -- daily, or even twice daily in hot, dry weather. Transplants may need daily watering until they've had a chance to send their roots out into the surrounding soil. Once established, most plants need a deep, weekly drink, if nature doesn't supply it.
Examine your yard for areas with standing water, such as old tires or upturned garbage can lids, and dump them. Mosquitoes breed in these types of places, so by removing them you'll get a head start on controlling the pests. In ponds and water gardens, use mosquito dunks -- disks that contain a specific strain of Bt (Bacillus thuringiensis) that controls the mosquito larvae.
Although it can be painful, it's important to thin seedlings to the proper spacing so they can grow freely. Properly spaced plants will mature faster and have fewer disease problems. Use the thinnings from beets, kale, spinach, and lettuce in a salad mix.
Use iron phosphate-based baits to control slugs and snails. Simply sprinkle the little pellets around the base of plants, and like magic, no more slug damage. Unlike some of the older slug baits, these are safe to use around pets and children, and they're less messy than beer traps.
When spring-flowering dianthus plants begin to flag, cut them back to about 4 inches from the ground. This will tidy them and encourage them to produce a second flush of flowers. The same advice holds true for many other shrubby perennials, such as catmint.