Ranunculus plants, more commonly known as buttercup plants, have green leaves that grow in a mound about 6 to 12 inches in diameter. Bulbs planted in fall will flower in March -- or in June or July if the bulbs are planted in spring. Flower colors range from yellows, reds, pinks, gold or bi-colors, depending on the variety. Plants need proper care to prevent the green foliage from turning yellow.

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Buttercup flowers growing on healthy, green foliage.

Light

Ranunculus plants need full sunlight to grow and flower. If you plant the bulb in a location with shade, the leaves will prematurely turn yellow. Plants need at least six hours of sun when actively growing. However, if you have a potted houseplant, you need to give the plant full sunlight, but keep the room temperature below 60 degrees F, or the leaves will start to turn yellow and die.

Nitrogen

Plants need fertilizer weekly. If the leaves are turning yellow, the plant may need more nitrogen in the soil to promote green foliage. Use a water-soluble fertilizer such as 15-16-17. Apply the fertilizer every week during the growing season, but only after the plant shows signs of growth in spring.

Crown Rot

Crown rot appears to start on the ranunculus plants when the weather is humid and hot. The lower leaves on the plant will start to yellow and turn brown at the base of the plant. The upper leaves will wilt and will turn yellow as well. Plants that suffer from crown rot should be discarded, and any soil must be sterilized to remove the fungi.

Natural Cause

After the ranunculus plant has finished flowering, leave the plant and foliage alone until the leaves turn yellow. The plant will gather energy for the bulb for the next growing season if you leave the foliage until the leaves turn yellow. After the leaves turn yellow in fall, you can cut the foliage off at the base of the plant so the bulbs can rest until the next growing season.