Understanding the longevity of weed seeds in soil is crucial for effective garden and lawn management. OSU Extension Service reveals that the survival span of weed seeds varies significantly by species. For instance, annual bluegrass seeds may persist for up to about five years, while wild oats can survive between three to six years, potentially longer in deeper soil layers. Jointed goatgrass and barnyardgrass seeds have a survival range of three to five-and-a-half years and up to 13 years, respectively. Quackgrass and common velvetgrass can endure up to four and over ten years, respectively. Mustard seeds are known for their particularly long lifespan.
Despite the common myth, topsoil invariably contains weed seeds, as noted by MSU Extension. Completely eliminating these seeds is virtually impossible without damaging the soil’s microbial life, a crucial component for healthy soil. This suggests that even high-quality topsoil can be a source of weed seeds.
One method to manage weed growth is using landscape fabric, as suggested by Illinois Extension | UIUC. This fabric can suppress weeds temporarily, but it’s not a permanent solution since new weed seeds can still invade the area.
Contrary to what might be assumed, many weed seeds do not remain viable for long periods. Penn State Extension explains that a significant number of weed seeds are either non-viable, consumed by wildlife, or decompose relatively quickly. However, there can still be millions of viable seeds per acre, ready to germinate under favorable conditions.
Weeds can also be indicators of soil health, as MSU Extension points out. Certain weeds thrive in specific soil conditions, such as poorly drained or low pH soils. Adjusting these conditions can be a natural way to manage weed growth.
When it comes to weed control in gardens, UMN Extension suggests using pre-emergent herbicides that inhibit weed seed germination. However, these herbicides are not effective against all weed species and do not affect already existing weeds.
In lawn management, Penn State Extension recommends pre-emergence herbicides for annual grass weeds like crabgrass. Timing is critical for these herbicides to be effective.
For vegetable gardens, UC Weed Science – ANR advises against deep tilling, which can bring dormant weed seeds to the surface. Soil solarization is an alternative method, using the sun’s heat to sterilize the top layer of soil and eliminate weed seeds.
Dormant seeding, a technique recommended by UMN Extension, involves sowing seeds during cold periods, allowing them to germinate as the soil warms. This method can provide a head start in establishing a lawn, reducing the window for weed growth.