Astrantia, more commonly known as masterwort, are clump-forming, flowering perennial plants that thrive in partially shaded locations with moist soil. The plants are prized for their unusual-looking blossoms, which are actually tightly-packed flowerets surrounded by petal-like bracts. Astrantia performs best in U.S. Department of Agriculture (USDA) plant hardiness zones 4 through 7. If your astrantia is refusing to flower, make sure you are meeting its cultivation requirements and give it a good pruning to stimulate new growth.
Astrantia are shade-loving perennials but, like most flowering plants, they require some exposure to sunlight in order to bloom. If planted in a deep-shade location, astrantia may flower poorly, or not at all. When selecting a planting location for your astrantia, look for a site that receives bright indirect, or filtered, sunlight for three to six hours each day, preferably in the morning and early afternoon.
Astrantia plants love moisture and need consistently moist soil to thrive. If the soil your astrantia is growing in is too dry, the plant may fail to produce flowers in an attempt to conserve moisture. Provide the astrantia with regular supplemental irrigation during the spring and summer months, when the plant is actively growing. Approximately 1 inch of water per week should be sufficient in most cases; skip the weekly watering if the plant has received an equivalent amount of rainfall.
Fertilise astrantia regularly while it is actively growing to give your plant the nutrients it needs for healthy growth and development. Improper fertilisation, such as over-fertilising or using the wrong type of fertiliser, may damage your plant or cause it to produce an excess of foliage at the expense of flowers. For best results, feed your astrantia monthly with a balanced, water-soluble fertiliser. As soon as the plant sets its buds, supplement your regular fertilisation schedule with a single application of a high-phosphorus, "bloom booster" fertiliser.
Prune Astrantia to Simulate Growth
Astrantia plants should be cut down to the ground at the end of the growing season to promote vigorous spring growth. Online resource The Garden of Paghat suggests using this technique in the middle of the growing season, if necessary, to invigorate your astrantia's growth and blooming. Use a pair of sharpened and sterilised pruning shears to cut the plant's foliage down to just 2 to 3 inches above the surface of the soil; the pruning may seem harsh, but the plant will quickly recover and bloom prolifically.