How To Remove Weed Seeds From Soil

Yard and Garden News Landscape fabric also works well to suppress weeds. It is most appropriate for transplanted vegetables, since holes can be cut into it to plant seedlings. Mulch can be Make a Withdrawal from your Soil Weed Seed Bank: Stale Seedbed Technique Ah spring! The war against weeds begins anew. The first major skirmish of the growing season should happen before One method of weed control is to remove weed seeds in the fallow, stubble and pre-sowing phase. This can be achieved by encouraging the germination of weed seeds and then subsequently killing seedlings or destroying seeds and reducing seed viability. This section covers the different methods used to deplete weeds.

Yard and Garden News

Landscape fabric also works well to suppress weeds. It is most appropriate for transplanted vegetables, since holes can be cut into it to plant seedlings.

Mulch can be applied at any time, but it is generally a good idea to wait until late spring, once the soil has warmed. Vegetables need warm soil to grow, and applying mulch too early will keep the soil cool for longer into the spring, potentially slowing the growth of vegetables.

In particularly wet years, mulching too early can also create habitat for slugs that chew on vegetable leaves.

2: Throw away or burn mature weeds – Do not compost them.
If left to grow, one common lambsquarter plant can produce over 70,000 seeds on average. Photo: Annie Klodd

The best way to control weeds is to not have them in the first place. Fortunately, there are ways we can help reduce the amount of weed seeds that get into our garden’s soil.

The most important tip is to never leave mature weeds in the garden, otherwise they will deposit their seeds into the garden soil and lead to more weeds in the future. Did you know. weed seeds survive in the soil for several years, and some common species can produce hundreds of thousands of seeds per plant?!

That’s why you should always remove weeds before they are mature enough to flower and produce seeds. But if weeds do grow to maturity, remove them as soon as possible and either dispose of them or burn them – do not leave them in or near the garden, and do not put weeds in the compost pile if they have flowered or have seeds on them.

Composting can only kill weed seeds if all parts of the pile reach at least 140 degrees F for an extended period of time. While some commercial farms and composting facilities achieve these temperatures in large piles that are turned regularly, ideal conditions are challenging to achieve in a home garden setting.

3: Use the hoe and tiller wisely!
Tilling a garden on May 8, 2018, about three weeks before planting warm-season vegetables.
Photo: Annie Klodd
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Have you ever noticed big flushes of new weeds after you till your garden soil in the spring? When we till, hoe or rake the soil, that disturbance does uproot existing weeds, but it can also lead to new weeds. This is because tilling stimulates buried weed seeds to grow by exposing them to the sunlight and warm temperatures that they need to thrive.

Using tillage strategically, and understanding a bit about how weeds grow, can help reduce weed problems before even planting the vegetable garden in the spring. A tillage technique called a “stale seedbed” aims to do just that.

Try the stale seedbed technique

In the stale seedbed technique, the soil is tilled or hoed just once, about 2-4 weeks before planting. This purposefully forces weed seeds to emerge early, before the vegetables are planted. The soil is then left undisturbed until it is time to plant.

Right before vegetable planting, the surface of the soil is raked or hoed again to kill the emerged weeds. After planting, try not to disturb the soil again, in order to discourage new weeds from coming up. A mulch or landscape fabric can be laid down at this time in order to suppress further weed seeds from emerging.

It helps you begin the season with a head start on the weeds, and what gardener doesn’t like that?!

Make a Withdrawal from your Soil Weed Seed Bank: Stale Seedbed Technique

Ah spring! The war against weeds begins anew. The first major skirmish of the growing season should happen before planting. The stale seed bed technique is an often over-looked practice that can be used before planting. It works by first encouraging weeds to sprout and then killing them when they are young and most vulnerable. For organic growers, a stale seed bed can replace the effects of a pre-emergence herbicide. And when used properly, it can contribute to both short-term and long-term weed management.

Weed control can be handled with short-term or long-term approaches. Short-term management focuses on controlling weeds during the first part of crop growth when weeds are more likely to affect crop yields. Long-term weed management, however, works all season-long to deplete weed seeds from the seedbank (the reservoir of viable weed seeds in the soil). Whichever approach you take, using a stale seed bed is a great cultural weed control technique.

To use the stale seed bed most effectively, start several weeks before planting. An initial cultivation kills any emerged weeds that have overwintered. It also brings weed seeds to the surface where exposure to light and oxygen stimulate germination. Depending on the weather and types of seeds present in the soil, weeds may sprout up overnight or over a few weeks. When weeds have germinated and are still small and young, they are easy to kill with a second light cultivation. This process is then repeated as needed and as time allows. As few as three cycles of light/ shallow tillage can reduce the number of subsequent weeds noticeably. For fields and gardens with very heavy weed infestations more cycles of repeated tillage over a few years will be needed. Using a stale seed bed may push back your planting date; but in the absence of weed competition, the crop will have more access to water and sunlight and be able to make up for lost time.

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Keys to Success

  • Do not allow emerged seedlings to grow large. It is best to till lightly just as the first seedlings are emerging as this and the earlier ‘white thread’ stage are the most susceptible to desiccation. The more time new weeds have to develop roots, the harder they become to kill with a shallow cultivation.
  • Keep the cultivation shallow to avoid bringing new weed seeds to the surface. The implement used to stir the soil should not go deeper than 2 inches with most of the stirring in the top inch.
  • The technique is dependent upon having adequate soil moisture. Under drought conditions preparation of a stale seedbed may require irrigation to stimulate weed seed germination.
  • Deeper initial tillage can be usedto bury an existing weed problem. Tillage, especially when done with a disc or a power tiller, distributes the previous year’s weed seeds throughout the top 6 inches or so of soil. In contrast, an inversion tillage that turns sod upside down will place last year’s seeds 6 inches or so under the surface. From there they are unlikely to emerge unless further discing or lighter tillage moves them closer to the surface. Used skillfully, a deep inversion plowing followed by stale seed bed can put a serious surface weed problem out-of-sight and out-of-mind, at least until the next time the field is plowed deeply.

Stale Seedbed is most effective when it’s part of a zero weed threshold system.

The common short-term approach to managing weeds(which weed scientists usually call the “critical period approach”) is to control weeds aggressively during the first 4-6 weeks after the crop is planted. This 4-6-week period is the critical period during which crops stands are established and yield is secured. Afterwards weeds are of less threat to production; therefore, many farmers scale back control efforts. However, weeds that grow before and after the critical period are still a problem. If allowed to flower and set seed, they will be planting a future crop of weed problems. A long-term approach to weed management, called zero weed seed threshold, requires constant diligence and removal of all weeds before they produce seeds–even after harvest. Research indicates that 3-4 years of using this approach will result in a field with relatively few weeds, provided weed seeds are not introduced from without the field (in seed, irrigation water, on equipment, etc.).

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Both short-term and long-term approaches have benefits and drawbacks, many of which depend on a farmer’s individual goals, crops, and available resources. A new online tool from Ohio State allows farmers to think through various weed control approaches in the context of their own individual situations. For those looking to make changes to their weed management, the Organic Weed Decision Making Tool, shows pros and cons of various strategies over time and gives steps to implementing new tactics. Learn more at go.osu.edu/eco-weed-mngt.

Crop weeds: reduce weed seed numbers in the soil

Please note: This content may be out of date and is currently under review.

One method of weed control is to remove weed seeds in the fallow, stubble and pre-sowing phase. This can be achieved by encouraging the germination of weed seeds and then subsequently killing seedlings or destroying seeds and reducing seed viability. This section covers the different methods used to deplete weeds.

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Different weed control methods

Burning crop residues

Burning can reduce the surface seed banks of many weeds. All crop residues (canola, wheat, lupin and others) can produce a sufficiently heated burn to kill weed seeds. A narrow windrow will burn at a higher temperature and improve weed seed kill.

Encouraging insect predation of seed

Weed seeds provide a major component of many insect diets (predominantly ants). There are methods to increase populations of insects over the summer/autumn fallow and therefore increase insect consumption of seeds.

Inversion ploughing

Fully inverting the soil will ensure that weed seeds that were on or just below the soil surface are placed at a depth from which they cannot germinate. This can be practiced every 8-10 years, with conservation tillage used in the intervening years. In Western Australia, annual ryegrass seeds failed to establish and eventually died when soil was fully inverted to a depth of greater than 20 centimetres (cm) using a specialist mouldboard plough fitted with skimmers. This single soil inversion event reduced annual ryegrass numbers by over 95% at Katanning and Beverley for a period of two years.

Autumn tickle

This does not destroy seeds but rather buries them to a depth of 1-2cm, enhancing seed germination by increasing contact with soil moisture. This encourages weed seeds to germinate earlier. A delay between the tickle and seeding is necessary to give an opportunity for the weeds to germinate and then be killed using a knockdown herbicide. The delay to seeding will result in a yield penalty for some crops.

Delaying sowing

This allows greater germination of weeds in particularly weedy paddocks, which can then be killed using a knockdown herbicide or cultivation prior to crop sowing. The longer the delay in sowing, the more weeds germinate and the higher the kill. However, a yield penalty is experienced when sowing is delayed.