Some tips to nip those weeds in the bud:
Weeds in sidewalks/driveways:
Carefully pour a small amount of bleach, ammonia or any caustic cleaning fluid over them.
Douse them with scalding water.
Dig them out with a hand hoe like the one pictured here (it's sometimes called a Cape Cod weeder), then sprinkle salt in the cracks.
Weeds in planting beds:
Pull by hand, being careful not to shake or disperse seeds. Weeds are incredibly efficient self-seeders; don't make it any easier for them to reproduce. Hand weeding is easier in moist soil. Pull slowly and firmly; if you yank, you'll probably end up with a fistful of leaves while the roots stay underground. This is the best method if you're trying to get rid of weeds that are growing in and among "good" plants.
Hoe them. There are several types of long-handled hoes, but one of the easiest to use is the stirrup or scuffle hoe, pictured on this page. You push it back and forth across the soil surface in short strokes _ easy on the back. Hoeing works best in dry soil and in beds where the weeds are between rows of plants.
Hit them with an herbicide. If you're fighting grassy weeds (not broadleaf ones), try fluazifop (brand name Grass-B-Gon). Be careful, though. It will injure or kill not only grassy weeds but also grassy-type ornamentals such as daylily, liriope (lilyturf) and mondo grass, all common plants in Florida landscape beds. For broadleaf weeds, try spot applications of a non-selective herbicide containing glyphosate (RoundUp or Ortho Kleenup) or an herbicidal soap spray (Safers or Sharpshooter).
Smother them. If weeds are growing in one well-defined area, say between rows of vegetable plants or flowers, you can smother them with a wooden board. It couldn't be simpler: Lay the board on top of the weeds. Leave there for a week. No more weeds! This method also will hold down spreading weeds such as Johnson grass and Bermuda grass until you have a chance to dig them up.
Weeds in lawns:
Hand-pull if you're a glutton for punishment and have lots of free time.
Otherwise, you'll need a good selective herbicide that kills only broadleaf weeds and not grass. Try 2,4-D and tricamba (Trimec) for Bahia lawns and atrazine for St. Augustine lawns. (Note: Do not use herbicides that are designed for lawns, especially weed-and-feed products, in landscape beds unless the herbicide is also labeled for use on ornamentals. Landscape plants are susceptible to damage from atrazine and phenoxy-type herbicides, common ingredients in lawn products.)
Stopping weeds before they start:
If you have a bare planting bed you want to treat before planting, here are some methods to make it weed-free:
Solarize. Place a large sheet of plastic on the bed and weight it down with bricks or paving stones around the edge. The Florida sun will cook any plant life under the plastic as well as kill weed seeds before they sprout.
Mulch. A thick layer of mulch is one of the best weed deterrents there is. For extra protection, lay down several sheets of newspaper or a woven landscape fabric, then cover that with mulch such as bark chips or pine straw, for a natural look.
Use a pre-emergent herbicide, which prevents weeds from germinating. Work it into the soil, either with a hand cultivator or by spraying it on the bed and watering well with overhead sprinklers. Many pre-emergent herbicides are specific in what weeds they kill; check the label. Look for trifluralin (Treflan) and oryzalin (Surflan). Those two are generally safe for use on landscape beds and will help control weeds for 10 to 12 weeks. Weeds that grow near your landscaped beds and those that have been a problem in the past will have to be sprayed regularly over the next several years. Weed seeds usually remain viable for three to five years in the soil.
Some gardeners think weeds can be tossed on the compost pile like any other garden trimmings. Be careful; many weeds are tough, and they'll sprout in your compost pile if it doesn't generate enough heat to cook them. A safer method: Dump the weeds in a wheelbarrow and leave it in the sun for several days until they're really dead. (If it rains, park the wheelbarrow in the garage or some other place where the weeds will continue to dry out), then you can safely compost them.
Sources: Pinellas County Cooperative Extension Service, The Weed Book , Mac Perry's Florida Lawn and Garden Care, Florida Lawns and Gardens by Lewis S. Maxwell and Organic Gardening magazine.