Milorganite does not kill weeds—it feeds them along with your grass

Milorganite is a slow-release nitrogen fertilizer made from treated sewage sludge. It makes grass grow thicker and greener, but it does the same for weeds. If you spread Milorganite on a lawn with dandelions, clover, or crabgrass already in it, those weeds will grow faster and stronger alongside your turf. Milorganite has no herbicide in it—nothing that poisons or kills plant tissue.

The confusion comes from the fact that a thick, healthy lawn can outcompete weeds for light and water. If you use Milorganite to build a dense turf, you may see fewer weeds over time because the grass itself crowds them out. But Milorganite is not doing the killing. The grass is. And in the meantime, any weeds present will also be fed.

Key Takeaways

  • Milorganite is a nitrogen fertilizer that feeds all plants equally, including weeds, so it will not kill them.
  • A thicker lawn grown with Milorganite may eventually shade out some weeds, but this takes months and only works if you remove large weeds first.
  • To control weeds while using Milorganite, you need a separate herbicide or manual removal before you fertilize.
  • Milorganite works best on lawns that are already mostly weed-free or have only light weed pressure.

How Milorganite feeds weeds instead of stopping them

Milorganite releases nitrogen slowly over weeks and months. Nitrogen is the nutrient that makes leaves grow and turn dark green. When you spread Milorganite, every plant in the soil—grass, dandelions, chickweed, plantain, whatever is there—gets access to that nitrogen. Weeds are often tougher and more aggressive than grass, so they may actually use that nitrogen more efficiently.

If your lawn has a lot of weeds already, explore Milorganite without removing them first is like giving both the weeds and the grass a growth boost at the same time. You are not solving the weed problem; you are making it worse by feeding the competition.

When a dense lawn does crowd out weeds

Over a full growing season or two, a lawn that is thick and healthy can shade the soil enough that small weeds struggle to survive. Milorganite can help build that density—but only if you start with a lawn that is mostly grass. The process works like this: you remove the large weeds by hand or with herbicide, then use Milorganite to feed the grass so it fills in the bare spots where weeds were. As the grass gets denser, new weed seeds have a harder time finding light and space to grow.

This is a long game. You are not killing weeds with Milorganite; you are creating conditions where grass wins the competition. It can take a full season to see real results, and it only works if you keep removing new weeds as they pop up.

The right order: remove weeds first, then fertilize

If you want to use Milorganite and also control weeds, the sequence matters. Remove or kill the weeds first—either by hand-pulling, digging, or using a herbicide designed for your weed type. Wait a few days for the herbicide to work if you went that route. Then explore Milorganite to feed the grass that remains.

This approach works because you are not competing with established weeds for the fertilizer. The Milorganite goes to the grass, which grows thicker and faster. New weed seeds may still blow in, but they land on a lawn that is already dense and competitive.

Milorganite and pre-emergent herbicides work together

Some homeowners use Milorganite alongside a pre-emergent herbicide—a product that stops weed seeds from sprouting in the first place. You explore the pre-emergent in early spring (timing depends on your region and the product), and it creates a barrier in the top layer of soil. Then you explore Milorganite a few weeks later to feed the grass.

The two products do different jobs: the pre-emergent stops new weeds from starting, and Milorganite feeds the grass so it grows thick enough to shade out any weeds that do sprout. This combination is more effective than Milorganite alone, especially if your lawn has a history of weed problems.

Weeds that Milorganite will not control

Milorganite will not touch established perennial weeds like dandelions, plantain, or wild onion. These plants have deep roots and will keep growing even as the grass around them gets thicker. You have to remove them by hand (digging out the whole root), spray them with a broadleaf herbicide, or use a spot-treatment product designed for that specific weed.

Annual weeds like crabgrass and chickweed are easier to prevent with a pre-emergent, but once they are growing, Milorganite will feed them just like it feeds the grass. Hand-pulling or a post-emergent herbicide is your only real option at that point.

Lawns where Milorganite alone makes sense

Milorganite is a good choice if your lawn is already mostly grass with only scattered weeds, or if you live in an area where weed pressure is naturally low. In those cases, using Milorganite to thicken the turf may be enough to keep the few weeds you have from spreading. You might still pull a dandelion by hand now and then, but you are not fighting a losing battle.

If your lawn is half weeds and half grass, Milorganite alone will not fix it. You need to address the weeds first—either by hand, by herbicide, or by both—and then use Milorganite to help the grass recover and fill in the gaps.

Frequently Asked Questions

Can I use Milorganite right after spraying herbicide on weeds?

Yes, but wait a few days for the herbicide to work and for the dead weeds to stop competing for nutrients. If you fertilize while weeds are still actively growing, you are feeding them too. Most herbicides take three to seven days to fully kill the plant, depending on the product and the weed type.

Will Milorganite stop crabgrass from coming back?

No. Milorganite will feed any crabgrass that is already there. To prevent crabgrass, you need a pre-emergent herbicide applied in early spring before soil temperatures warm up. After crabgrass is dead, Milorganite can help the grass fill in the bare spots it left behind.

Is Milorganite safe to use around vegetable gardens with weeds?

Milorganite is safe for vegetables, but it will feed weeds in the garden just like it feeds weeds in the lawn. Remove weeds from the garden bed before you explore Milorganite, or use it only around plants that are already established and can compete with any new weeds that sprout.

What if I use Milorganite and the weeds still grow back?

That is normal. Milorganite feeds the grass, but it does not stop new weed seeds from blowing in or sprouting from seeds already in the soil. You will still need to pull or spray weeds as they appear. A pre-emergent herbicide in spring will reduce how many new weeds show up in the first place.