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How Do I Grow Iris Bulbs?

Angie Bates
Angie Bates

Some of the most striking perennial flowers planted in gardens, irises belong to a group called reticulata bulbs. Irises are low-maintenance flowers that are relatively easy to plant and do not require exceptionally fertile soil to grow. They can, however, be extremely susceptible to overwatering, over-fertilization, and insufficient sunlight, so it is important to take care the of exact needs of the flowers when planting iris bulbs.

Iris bulbs are actually rhizomes, which is technically a stem that grows horizontally. This means that once planted and allowed to grow, one rhizome can sprout multiple flowers at intervals. At a minimum, bulbs should be spaced 6 inches (15.2 cm) apart, though 1–1.5 feet (30–45 cm) apart is more highly recommended. They should be planted relatively close to the surface, between 2–4 inches (5–10 cm) deep.

Woman with a flower
Woman with a flower

Fall since this is the ideal time to plant iris bulbs, and this is usually the easiest time of the year to find them. Bearded, non-bearded, and dwarf varieties can usually be obtained. Bulbs should be planted before it gets so cold it begins to frost, but after the hottest part of the year.

When preparing to plant your iris bulbs, you should dig a hole a hole approximately twice the size of the bulb. The bulbs should always be placed into the holes so the leaves are facing up. It is important when filling in the hole that no air pockets are left around the bulb. Air pockets may cause root rot.

Another cause of root rot is soil that is not extremely well draining. Though irises do not need special soil to grow, soil that holds moisture, like soil with clay in it, will retain too much water to allow the irises to flourish. Iris bulbs should also be planted in areas that get a lot of full sunlight. Although they can survive with some partial shade, a minimum of six hours of full sun each day is necessary for these flowers to thrive.

Irises also do not tolerate large amounts of nitrogen fertilizer. Placing compost on the newly planted iris bulbs may help extend the life of the flowers, but afterward fertilizer should be used only sparingly. Water, as well, should be given only when conditions are extremely dry, since overwatering is the leading cause of root rot in these plants.

Rhizomes spread quickly, so the spaces between planted iris bulbs should fill in with iris flowers. Some rhizomes may even need to be periodically pulled up to thin the garden. Propagating these flowers is also a simple matter of splitting the rhizomes.

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      Woman with a flower