Will Ammonia Kill Grass, Weeds, And Other Plants?

Ammonia (NH₃) in various forms is a very popular and very important nitrogen fertilizer responsible for plant size and lush green leaves.

However, too much of something good is not necessarily better, on the contrary, too much ammonia can kill grass, weeds, and other plants. Read more ...

Published: March 27, 2023.

What Is Ammonia?

Ammonia is a Nitrogen (N) and Hydrogen (H) compound with a chemical formula of NH₃. At room temperature, Ammonia is a gas with a very specific smell.

Ammonia in many forms is part of NPK fertilizers, providing Nitrogen to the plants.

The most common forms of nitrogen fertilizers include:

• Ammonium Nitrate (NH₄NO₃): NPK 33-0-0,
• Ammonium Sulfate (NH₄)₂SO₄: 21-0-0, plus 24% Sulphur,
• Ammonium Dihydrogen Phosphate ((NH₄)(H₂PO₄)): 12-27-0, etc.

Note: Urea (CO(NH2)2) contains 46% Nitrogen (NPK 46:0:0), but the Nitrogen is part of the amino group (-NH₂) and not the ammonium cation (-NH₄).

Nitrogen fertilizers should be added as instructed by their manufacturers.

For example, the typical application of Ammonium Nitrate to the established lawn is 3 pounds per 1000 square feet (1 pound of nitrogen), evenly spread.

In such amount, Ammonia will not cause root and leaf burns and will not overload plants' root systems with excess nutrients.

When spreading lawn fertilizers, one should use fertilizer spreaders or try evenly to spread the required amount of fertilizers manually - it takes some practice but can be done successfully.

Note: when fertilizing with NPK fertilizers, it is better to apply lower amounts more often.

Does Ammonia Solution Kill Weeds?

Ammonia solution (house ammonia) contains 5-10% of Ammonium Hydroxide (NH₄OH) and is a very popular household cleaning agent.

Since household ammonia contains ammonia, it can be used as nitrogen fertilizer, right? Wrong!

When ammonia solution comes in contact with grass, weeds, and other plants (and human skin, for example), it causes chemical burns that eventually can kill (and in most situations, it will kill) various plants.

For household ammonia to be used as safe nitrogen fertilizer, it must be very diluted, offering plants very small amounts of nitrogen.

Thus, if You want to fertilize your, for example, lawn grass, use lawn grass nitrogen fertilizers. Similarly, when fertilizing garden plants, bushes, and trees, use suitable NPK fertilizers or add organic fertilizers in the form of compost, aged manure, worm castings, organic mulch, etc.

Note: If You have issues with weeds in the garden and lawn, the best solution, although not the easiest and quickest, is to remove the weeds manually, their roots included. If there is a large area to cover, various chemicals can be used, just be sure to use them as instructed.

For short: Ammonia sources that can cause ammonia burns include:

• too large doses of NPK fertilizers,
• fresh manure, especially fresh chicken manure,
• animal urine,
• household ammonia, etc.

How To Remedy Ammonium Poisoning?

If you notice a bald spot in your grass or garden after fertilization, the first suspect is fertilizer overdose - fertilizer probably wasn't spread equally.

Just in case, before doing anything, take a few samples and test them for pH and amount of macro- and micro-elements.

The easiest method, although not working always, is to flush excess fertilizers (and ammonia) down using plenty of water - NPK fertilizers are water-soluble compounds and can be washed away using water.

After all, that is the reason why sandy soils must be fertilized more often than other types of soil.

The required amount of water varies depending on the soil and fertilizer type and amount, but one can try to use 8-10 inches (yes, 8-10 inches) of water one to three days in a row.

After washing the soil patch, test it again for pH and other parameters - if everything is alright, sow some grass seeds (lawn) or plant new plants (garden).

The fastest, although not the easiest method, includes removing the soil from the affected surface and adding good potting soil mixed with some organic fertilizers and sowing new grass (lawn) right away or planting new plants (garden).

Note: if the lawn area is relatively small, even without sowing the new grass, the grass will cover it quickly. However, if You have some seeds left, feel free to sow them.

Few Final Words

Household ammonia (used as a cleaning agent) is not a suitable and safe source of ammonia for plants - if You need a fertilizer for your lawn or garden, commercial fertilizers (different NPK formulas) are much safer.

Which NPK fertilizer you will use depends on the plant type and growth stage - while grasses grow well when fertilized using nitrogen fertilizers (or fertilizers containing mostly nitrogen), some plants also require plenty of phosphorus and potassium for flowers and fruits.