Today 
Yarrow, Achillea millefolium, thrives in soils that are affected by long periods of drought or are lacking in nutrients. The plant spreads by underground stems and also by seeds from its flowers (June to October), which provide an excellent source of nectar for bees. However, once it is established in your garden it will quickly spread, causing particular problems when it appears in the lawn.
Solution
Organic
The most effective organic approach is to weaken the plant by hoeing it wherever it appears in beds or borders, or to dig it out using a fork or trowel. If it establishes itself in the lawn you will have to dig out chunks of grass to get it out effectively, but you can hold it at bay by keeping the lawn healthy and thereby making conditions less favourable for the yarrow. Top-dress the lawn in spring and in September, mow it regularly and lightly rake when in growth to weaken the weed.
Chemical
Yarrow is fairly resistant to many selective weedkillers, but in lawns, use a weedkiller such as a 2, 4-D-based herbicide to remove the weed. Apply in cool, moist, calm conditions when there is least risk of accidentally damaging nearby garden plants.
