Heat and time to destroy weed seeds

Heat and time to destroy weed seeds

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Temperature to Kill Seeds

Compost, potting soil and other garden amendments can harbor seeds from unwanted grasses and broadleaf weeds. You can prevent unwanted seeds from competing with your lawn and garden plants by using a heat treatment of the right duration and intensity. The exact temperature needed to kill a seed depends on the species of plant it came from, but in most cases heating seeds to 140 degrees Fahrenheit is sufficient to sterilize them, reports Cornell University.


Seeds begin to die at temperatures above 108 degrees Fahrenheit, but require longer periods of exposure at lower temperatures. At temperatures below 140 degrees Fahrenheit some species are not affected by heat treatments. The most effective way to ensure that you kill all of the seeds is to heat them to a temperature above 140 degrees Fahrenheit. Seeds mixed into compost or topsoil require higher temperatures and longer exposure times than bare, unprotected seeds.

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Compost piles that reach and maintain a temperature of at least 140 degrees Fahrenheit for at least two weeks will kill most seeds within the pile. It is important to turn your compost pile so that it composts evenly since the hottest part of the pile is at the center, says Texas A&M University AgriLife Extension. Seeds left on the outside or bottom of the pile may not reach a high enough temperature to thoroughly kill all of the seeds inside.

Heating Soil

You can quickly kill seeds and harmful micro-organisms in soil using your kitchen oven. Heating your soil to temperatures between 180 and 200 degrees Fahrenheit will kill any seed in the soil after 30 minutes. The best way to heat treat your soil is to place it in a pan in the center of the oven. Make sure that the soil is about 4 inches deep so that it heats evenly. You can monitor the temperature of your soil using a standard oven thermometer.


Heating your soil above 200 degrees Fahrenheit can cause certain types of soil with a concentration of organic matter to release a foul odor. In some cases overheating your soil can also begin a chemical reaction in the soil that will release a chemical that is harmful to plants. Large compost piles in excess of 7 feet in height that are heated to 200 degrees Fahrenheit or higher may combust. The optimal temperature for creating compost and killing seeds is between 130 and 150 degrees Fahrenheit. You can monitor the internal temperature of your compost pile using a temperature probe. If your compost pile begins to overheat, cool it off using water, reduce the size of the pile or add a bulky material such as wood chips.

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How to Kill Weed Seeds in Soil [5 Easy Methods]

To kill weed seeds in soil you will have to apply one or more of the following methods:

  • Heat soil to temperatures high enough to kill weeds seeds
  • Force seeds to sprout and destroy growing weeds
  • Apply chemical or natural weed killers that prevent weeds from sprouting
  • Use flame weeding to destroy weeds and seeds at once
  • Layer mulch in garden areas to suppress weed sprouting and attract insects that eat seeds

With this arsenal of tricks for killing weed seeds before they sprout, you can stop the spread of weeds in both your lawn and garden.

Table of Contents

5 Tips for Killing Weed Seeds

Rather than spending time and effort battling weeds as they sprout, attack weeds at the source by killing weed seeds. Each of these methods destroys weed seeds, which ensures you won’t have to battle recurring weed invasions. Try these ways to get rid of weed seeds yourself.


Soil solarization is a very powerful method for killing weed seeds. Weed seeds begin to die if soil temperatures surpass 108 degrees, with full seed death ensured by soil surface temperatures of 140 degrees or more. Solarization uses clear plastic tarps to trap heat at the soil surface, killing weed seeds within the tarped area. To solarize an area, follow these steps:

  • Clear the area of all vegetation through use of a hoe or other garden implement. Remove any woody stumps
  • Till the soil to further break up any weed root systems left behind.
  • Rake away all vegetation residue
  • Water the tilled and cleared soil with a garden hose until it is damp.
  • Lay a sheet of clear plastic over the area. Weigh it down tightly at the edges
  • Leave the plastic in place for at least two months.
See also  Shelf life of weed seeds

Solarization is the best method to reclaim a weedy garden or other area. It is a “clean slate” for your soil, because seeds will be destroyed by the solar heat trapped beneath the plastic.

It is typically tough to implement solarization in large areas and is not usually suitable for use in lawns, where you may want to preserve grass or other plants. Pre-emergent weed killers and flame weeding are much better for use in lawns.

Till and Kill

Weed seeds can lie dormant in soil for decades and are only “activated” when brought to within an inch of the surface. One method to rid soil of dormant weed seeds is to force these dormant seeds to sprout, then attack them with a powerful natural or chemical weed killer. To do this:

  • In spring, till the affected area. Tilling brings dormant seeds to the surface
  • Water the area for 1–2 weeks with a sprinkler or soaker hose
  • When weeds begin to sprout, apply the weed killer of your choice

This is another “clean slate” method, where you force weed seeds to show themselves and then kill young weeds before they mature and cast seeds. Because of the invasive tilling step, it is not best used in areas with desirable grasses and plants.

Use Pre-Emergent Weed Killer

Pre-emergent weed killer stops weeds in their tracks. It works by attacking weed seeds just as they begin to germinate, killing them before they even poke above the surface. It’s a weed killer so good, the only sign it’s working is that there will be no new weeds at all.