Can You Apply Preen Before the Flowers Grow?

Before Planting Flowers

• Preen works as a pre-emergent herbicide, meaning it stops weed seeds from achieving the right conditions for germination. However, the herbicide can't always distinguish between a weed seed and a flower seed. When growing flowers from seed, always sow the seeds and let the plants get a good head start before applying the weed preventer. It's not designed to stop existing plants from growing, but it can keep flower seeds from sprouting.

Before Flowers Appear

• After your seedlings reach 2 to 3 inches tall, it's safe to apply the weed preventer even if the plants don't have flowers on them yet. Flower species bloom at different times of the year, so whether the plants are in bloom isn't a deciding factor on whether to apply Preen. Apply the weed preventer around established flowers at any time during the growing season, but give new seedlings time to become established before using the herbicide.

Application

• Getting Preen into the top inch of soil is key to preventing weeds. Scatter the granules at a rate of about 1 ounce per 10 square feet of flowerbed space, then water the bed thoroughly to help the herbicide sink into the top layer of soil. If you have mulch in your flowerbed, the procedure is the same, although it might take a bit more water to get the granules into the soil below.

Considerations

• Preen isn't designed to kill existing plants, but if the product touches the leaves or roots directly, it can cause some damage. It can discolor the leaves and create damaged spots on the roots, so brush away any granules that touch your plant blooms or leaves as well as those that fall directly on top of existing flowers' root systems. Reapply about every three months for the best weed control, as long as you're not planting flower seeds at the same time.