Buttercup is a lovely looking flower, though it is generally considered a weed. It's one you may choose to tolerate if it's not preventing you from growing other intended plants, as it's quite difficult to eradicate.
The Botany and Biology of Buttercups
Botanically, buttercups are a type of Ranunculus, but they are different than the types of Ranunculus grown for cut flowers. Buttercups have small, yellow flowers (no more than an inch across) and leaves that are slightly larger, usually separated into three or five sections, each of which is deeply divided.
There are many species of buttercup, but the most common species that gardeners will encounter is the creeping buttercup (Ranunculus repens). This species grows only two or three inches tall, spreading across the ground with short runners. It is extremely common in lawns in nearly every corner of the country, though it will invade flower beds and shrub plantings as well.
It thrives with full sun, ample moisture and rich soil, but is capable of surviving under adverse conditions. The reason is that it stores energy in its fleshy rhizomes, which will survive in less than optimal conditions, such as drought. The leaves may die, but the rhizomes survive several months without leaves and sprout again when conditions improve.
Living With Buttercups
Many gardeners choose to tolerate buttercups and enjoy their profusion of flowers in spring. They commingle with grasses quite well and will certainly not cause a lawn to die out.
Buttercups are most troublesome in beds of annual flowers and vegetables where they compete directly. Around taller perennial plants and shrubbery, however, they can be seen as an attractive groundcover. They will provide a small degree of competition to larger plants, but it may be worth learning to coexist with buttercups rather than attempt the enormous task of eradicating them.
Options for Control
The resilience of buttercups' tiny rhizomes is what makes them difficult to eradicate. You may spend hours weeding them only to find a few weeks later that they are completely re-established. The rhizomes tend to snap off in the ground when they are pulled, making this form of weeding somewhat futile, especially over large areas.
Small Areas By Hand
In a small area, it's possible to first loosen the soil with a digging fork and then carefully sift through it with your fingers to remove all the little root pieces. It's much easier if you approach it this way rather than pulling the tops and then trying to find the roots, as the roots will still be connected to the tops for the most part.
Buttercup can be controlled, but not necessarily eradicated, with the use of herbicides. Buttercups are a major agricultural nuisance and have been sprayed with herbicides for so long that resistant strains have developed in some areas. The plants will be weakened by herbicides, but repeated sprayings are generally necessary to keep the plants from re-establishing.
Given the environmental issues associated with herbicides, constantly spraying the landscape with them is best avoided. Plus, most herbicides will damage any other plants growing in the vicinity.
Tilling up an area that is infested with buttercups and allowing the rhizomes to dry out in the sun is a fairly effective method. This works best in the heat of summer during a period when no rain is forecast. Plan to leave the roots exposed on the surface for at least 10 days. The drawback of this method is that the grass or any other plants growing in the vicinity will be destroyed in the process. There will also be seeds in the soil that will sprout once moisture is available again.
This is a fairly effective technique, but it takes a bit of persistence. The idea is to cover the infested area with heavy duty black plastic, staking it securely to the ground, and leave it until the rhizomes are essentially starved for energy due to a lack of light for photosynthesis. To be most effective, the plastic should be left in place for an entire growing season. An added benefit of this method is that any seeds stored in the soil will be rendered unviable by the extreme heat that builds up.
Beautiful and Pesky
Whether you're in the camp that thinks buttercups are a gift from nature to enjoy or you feel they are the bane of your existence, learning a bit more about their biology will help to inform how you choose to manage their presence in the yard. Total eradication is difficult at best, so a combination of tactics is generally the best way to get rid of them, depending on how much they are impacting other plants that you want to grow.