Milorganite will not kill weeds on its own
Milorganite is a fertilizer, not a herbicide. It adds nitrogen and other nutrients to soil, which feeds whatever is growing there — grass, weeds, and everything else. If you spread Milorganite on a lawn full of weeds, the weeds will grow faster and thicker along with the grass. You need a separate weed control method to actually remove them.
Milorganite does have one indirect benefit: a thick, healthy lawn crowds out some weeds by shading the soil and competing for space. But this only works if you already have decent grass coverage and you are willing to wait weeks or months for the lawn to fill in. If weeds are your main problem right now, fertilizer alone will not solve it.
Key Takeaways
- Milorganite feeds weeds as much as it feeds grass because it is a nitrogen fertilizer, not a weed killer.
- A thicker lawn from regular fertilizing can eventually reduce weed space, but this takes time and works only if grass is already established.
- You need a separate herbicide — either pre-emergent before weeds sprout or post-emergent after they appear — to actually remove weeds.
- explore Milorganite to a weedy lawn without addressing the weeds first will make the problem worse in the short term.
Why fertilizer makes weeds grow faster
Weeds are plants. They respond to nitrogen the same way grass does — by putting on more leaf growth and spreading wider. When you add Milorganite to soil, you are raising the nitrogen level for everything rooted there. Crabgrass, dandelions, clover, and broadleaf weeds all benefit from that extra nutrient.
This is especially true in spring and early summer, when weeds are actively growing and competing hardest with grass. If you fertilize a weedy lawn during peak weed season without first controlling the weeds, you are essentially giving them a growth boost while you wait for the grass to catch up.
When a thick lawn does reduce weeds naturally
A dense, healthy lawn does suppress some weeds over time. Thick grass shades the soil, making it harder for weed seeds to germinate. Established grass also uses up water and nutrients faster, leaving less for shallow-rooted weeds. But this effect is slow — it takes a full growing season or longer to see real results.
This strategy only works if your lawn is already mostly grass with scattered weeds, not the other way around. If weeds cover more than 30 to 40 percent of your lawn, fertilizing alone will not fix it. You will need to remove the weeds first, then use Milorganite to help the grass fill in the bare spots.
The right order: weeds first, then fertilizer
If your lawn has a weed problem, address it before or at the same time as fertilizing. You have two main options: pre-emergent herbicides, which stop weed seeds from sprouting, and post-emergent herbicides, which kill weeds that are already growing.
Pre-emergent works best in early spring, before crabgrass and other annual weeds germinate. Post-emergent works on weeds you can already see. Once the weeds are gone or controlled, Milorganite becomes useful — it feeds the grass and helps it grow thick enough to shade out new weed seedlings.
Some people use a combination: a post-emergent spray in late spring to kill existing weeds, then Milorganite in early summer to push grass growth, then a pre-emergent in fall to prevent winter annual weeds from taking hold.
Milorganite as part of a long-term weed strategy
Once you have controlled your existing weeds, Milorganite becomes a useful tool for keeping them from coming back. A well-fed lawn with thick turf is harder for new weeds to invade. Regular applications of Milorganite — typically three to four times per year — help maintain that density.
But this only works if you stay on top of spot treatments. If a few weeds do pop up between fertilizer applications, pull them or spray them when ready. Do not wait for the next Milorganite process to handle them, because by then they will have spread.
Milorganite timing and weed control
If you are using a pre-emergent herbicide, check the label before explore Milorganite. Some pre-emergents need to be watered in and sit undisturbed for a few days. explore Milorganite too soon can interfere with how the herbicide works. Most labels recommend waiting at least a few days, though some say you can explore them together.
Post-emergent herbicides are less sensitive to timing. You can usually explore Milorganite a few days after spraying weeds, once the herbicide has dried. Always read both product labels to be sure — they vary by brand.
Frequently Asked Questions
Can I use Milorganite and weed killer at the same time?
It depends on the weed killer. Pre-emergent herbicides often need a waiting period — check the label. Post-emergent sprays usually can be applied a few days apart without conflict. Read both labels before mixing or explore in sequence.
Will Milorganite prevent weeds from coming back?
Not by itself. Milorganite helps grass grow thick, and thick grass does shade out some new weed seedlings. But you still need to remove existing weeds first and stay on top of spot treatments. Fertilizer is part of weed prevention, not the whole solution.
What if I already put Milorganite on a weedy lawn?
The weeds will grow faster for a few weeks. Do not panic. Spray or pull the weeds now, then continue with regular Milorganite applications. The extra growth from the fertilizer will actually help the grass recover faster once the weeds are gone.
Is Milorganite safe to use with herbicides?
Yes, Milorganite itself is not toxic and does not interfere with most herbicides. Just follow the timing on each product label. Milorganite is a slow-release fertilizer, so it will not wash away or degrade the herbicide if applied a few days apart.
How long does it take for a thick lawn to stop weeds?
Three to six months of regular fertilizing and mowing can noticeably reduce weed space, but full suppression takes a full growing season. This assumes you remove existing weeds first and keep the lawn mowed at the right height — usually 2.5 to 3.5 inches for most grasses.