How to Use Preplant Herbicide


Weeds are the bane of virtually every gardener in the world. Weeds rob flowers and vegetables of needed nutrients and water, and they can harbor harmful insects. On top of that they simply make gardens look uncared for. Rather than spend hours and hours digging up weeds once they emerge, many gardeners are opting for the use of a preplant, or pre-emergence, herbicide. This is a herbicide that is applied to the soil before your flowers or vegetables are planted and prevents weeds from growing in the first place.

Step 1

Water your garden area thoroughly to encourage the growth of weeds. Water every other day for six days.

Step 2

Spray the area with a non-selective, broad spectrum herbicide on the seventh day (24 hours following your last watering), making certain to wet the leaves of all the weeds and other vegetation in the plot. Do not spray if conditions are windy or if rain is forecast within the next 24 hours. Do not spray any plants you do not wish to kill.

Step 3

Rake off all dead vegetation seven days after spraying with the broad spectrum herbicide.

Step 4

Use a hoe or similar implement to break up the soil, especially the top layer. Rake the area with your hard steel rake, removing any roots or other debris and leveling the soil.

Step 5

Purchase a preplant or pre-emergence herbicide that contains benefin, pronamide, bensulide, dinitroaniline, napropamide, metolachlor or dichlobenil. No preplant herbicide prevents all weeds from growing. Preplant herbicides which contain two or more active ingredients are best. Talk to your local garden center for the best preplant herbicide for your particular situation, based on the kinds of plants you will be planting and the type of weeds you need to control.

Step 6

Spray the ground thoroughly with the preplant herbicide, following the manufacturer's instructions. Do not mix your herbicide any stronger than the manufacturer suggests. If using a granular preplant herbicide spread it on evenly using a fertilizer spreader and then water it into the soil as per the manufacturer's instructions.

Step 7

Plant your garden any time after spraying or applying granules and water (even immediately), but take great pains not to walk on the soil or disturb it any more than absolutely necessary. Your preplant herbicide forms a barrier in the top 1 inch of your soil which prevents weed seeds from growing once they begin to germinate. If this barrier is disturbed, then weeds may find a gap in the barrier through which they can grow. Some pre-emergence herbicides do affect vegetable seeds, and many brands affect flower seeds--read labels carefully and consult with your local nursery to find an herbicide that will not affect the seeds you intend to plant.

Step 8

Water normally. Preplant herbicides are designed not to be washed out of the soil.

Things You'll Need

  • Water
  • Hard steel rake
  • Hoe
  • Broad spectrum herbicide
  • Garden sprayer or fertilizer spreader
  • Preplant (pre-emergence) herbicide


  • University of Arizona: Lettuce Injury From Preplant Herbicides
  • Oregon State University: Top 10 Reasons Your Pre-emergence Herbicide Failed
  • Utah State University: Pre-emergence Herbicide in Vegetable Gardens
Keywords: applying preplant herbicide, using pre-emergence herbicide, killing weeds

About this Author

Larry Parr has been a full-time professional freelance writer for more than 30 years. For 25 years he wrote cartoons for TV, everything from SMURFS to SPIDER-MAN.