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Fertilize your alstroemeria when in bloom. Mulch alstroemeria to protect it. Divide your alstroemeria by the rhizomes for propagation.
You can feed alstroemeria with a high potash fertilizer each week during the growing season when your flowers are blooming. Potash fertilizer contains potassium to help your plants thrive. You should be able to find this type of fertilizer at your local garden shop or hardware store. Placing protective mulch around your alstroemeria can protect it from extreme temperatures. You can mulch with straw or bracken. Keep the mulch at least 2 inches (5 cm) from the alstroemeria stem to avoid rotting at the base of the plant. If you live in an extremely hot climate, you may want to place mulch around your alstroemeria in the summer. If you live in a cold climate, you should place mulch around your alstroemeria in the winter. If you want to get new plants from the ones you already have, cut the plant so that it's within 6 inches (15cm) of the ground. Two weeks later, dig all the way around the plant. Dig up the plant's rhizomes, or horizontally-running root networks, as well as all of the roots that branch off from them. Divide the rhizomes of the plant with a sharp knife and then replant the rhizomes 6 inches (15cm) deep and 12 inches (30cm) apart. Expect the newly planted rhizomes to flourish within 10 weeks of planting. Thin and transplant the rhizomes every 2-3 years during the spring.