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You can kill dandelions and prevent them from taking over your lawn using either natural organic or chemical controls. Chemical controls are efficient and effective. On the other hand, natural weed control is labor intensive but will always be more eco-friendly.
Dandelions will invade a thin, stressed turfgrass stands so the best way to
prevent dandelions it to maintain a dense and healthy lawn that will make it hard for weeds to grow -- a thick, vigorous lawn will keep many weeds out.
The Challenge of killing dandelions and preventing their return:
Dandelions are simple perennials, they have a long taproot that allows them to survive the winter and regrow in the spring. A tiny piece of the taproot is capable of forming a new plant.
New plants spread and sprout from seed. The bright yellow flowers form white puffballs full of seeds that are dispersed by the wind. Every plant is capable of producing hundreds of seeds that will multiply around your yard and neighborhood, winds will carry and spread them over several miles. These seeds will germinate throughout the growing season.
Dandelions will flower in the
spring and again in the fall.
The best time to attack them is right after they flower. Flowering and producing seeds takes a lot of energy, when
they have finished blooming they are
weakened by low food reserves in their taproots. This is the best time to physically remove by hand weeding or digging.
When pulling or digging, make sure the soil is moist and remove as much of the taproot as possible. Weeding tools like the Weed Twister, Weed Hound or a large flat-head screwdriver are helpful. You might have to dig a dandelion several times before it quits re-sprouting. Keep digging the new plants as they return and before they have time to form another large taproot.
Horticultural vinegar (20% acetic acid) can be used to spot spray dandelions.
Kitchen grade vinegar is not an effective herbicide, its acetic acid concentration is only 5%. The acetic acid concentration needs to be at least 20% to be an effective natural organic weed control.
Horticultural vinegar will only kill dandelion foliage - not the taproot - new plants will return from the taproot. Vinegar is also non-selective, take care to spray only weed foliage because it will kill any foliage that you spray - including your grass!
Citric Acid - Another non-selective organic option is herbicides that contain citric acid as the active ingredient (Burnout II is an example). These work the the same as vinegar, they will kill weeds and grass so take care to apply only to weed foliage.
Corn Gluten Meal
can sometimes be used as a natural weed and feed. It has been
observed to work as a pre-emergent herbicide - it prevents seedlings
from developing a root system - it will not kill mature dandelions.
Just be aware that CGM can be difficult to use as an herbicide - timing
and environmental conditions must be perfect for it to work. It is 10%
nitrogen by weight - making it a good natural organic fertilizer.
A weed is a plant that has mastered every survival skill except for learning how to grow in rows. - Doug Larson
Selective, post-emergence herbicides (referred to as broadleaf weed control) are the most effective dandelion killers that are safe for lawns. 2,4-D is an example of a selective and systemic post-emergent herbicide.
Late spring and fall is the best time to use broadleaf herbicides to kill dandelions.
Common brands available to homeowners and can be purchased at garden centers and home improvement stores include:
Clear Choice is an interesting new product that uses micro-technology to improve the penetration of active ingredients into the weeds - less active ingredients are needed to kill the weeds.
Glyphosate -- Roundup is the most common brand -- is a very effective weed killer that you can use in landscape beds, sidewalks and driveways.
Glyphosate is a broad spectrum (non-selective) herbicide. Just like the organic herbicides mentioned above, take care to only spray target weeds.
Roundup is a more effective than the natural products because it will kill the whole plant -- roots and shoots.
Crabgrass preventers (Pre-emergent herbicides) applied in
the spring before weed seeds germinate will also help to reduce the
amount of dandelion weed seedlings that germinate and grow in lawns.