When it comes time to water your
Spotted knapweed, you should not be shy about how much water you give. With the first two to three inches of soil dry, this plant will appreciate a long and thorough watering. Supply enough water to soak the soil entirely. The amount of water you add should be enough to cause excess water to flow through the drainage holes at the bottom of your pot. If you don’t see excess water draining from the pot, you have likely underwatered your plant. But do not let the water accumulate inside the soil, which will be very dangerous to the plant as well. Alternatively, a lack of water draining through the pot could indicate poorly draining soils, which is detrimental to the health of this plant and should be avoided. If the plant is outside, 1 inch of rain per week will be sufficient.