Irises, with their distinctive, colorful blooms, adapt well to container gardening, offering flexibility and portability for those with limited space. Growing irises in pots allows the plants to be moved to optimize sunlight, protect them from extreme weather, or rearrange a patio display. Container culture requires specialized attention to planting depth, soil composition, and seasonal care to ensure the irises thrive. This guide covers the specific requirements for growing these flowers successfully outside of the garden bed.
Selecting the Right Iris and Container
The choice of iris is important because they grow from two different structures: true bulbs or fleshy rhizomes. True bulb types, such as Dutch irises or Iris reticulata, are often the simplest for containers and are planted in the fall for spring blooms. While rhizomatous irises (bearded irises) are suitable, smaller varieties like dwarf bearded irises are better suited for pots. The size of the mature plant should guide the container choice to prevent the plant from becoming top-heavy and tipping over.
The container itself must have excellent drainage holes, as irises are highly susceptible to rot in waterlogged conditions. For standard bearded irises, a pot with at least a 2-gallon capacity that is wider than it is deep is recommended to accommodate the spreading rhizomes. Dwarf varieties may succeed in smaller 6- to 8-inch pots, but a minimum depth of 12 inches is often suggested to allow proper root development for most types. Terracotta or clay pots are often preferable because they are porous and allow excess moisture to evaporate more quickly than plastic containers.
The potting medium should be loose and fast-draining. A high-quality, peat-free potting mix works well, and adding perlite or horticultural grit can significantly improve aeration and drainage. Avoid garden soil because it compacts easily in pots, restricting root growth and impeding water flow. The goal is to create an environment where water flows freely, mimicking the well-drained, sunny conditions irises prefer in the ground.
The Step-by-Step Planting Process
Preparation begins by ensuring the container is clean and the drainage holes are unobstructed. Fill the container partway with the well-draining potting mix to establish the planting base. The depth and orientation of the iris structure depend on whether it is a true bulb or a rhizome.
True iris bulbs, like Dutch irises, are planted with the pointed side facing upward at a depth roughly twice the height of the bulb itself. This deeper planting provides stability and helps them flower reliably. For rhizomatous irises, such as bearded varieties, the fleshy rhizome must be planted almost entirely on the soil surface.
The rhizome should be placed horizontally, with the roots spread out beneath it. Cover the roots with soil so the top half of the rhizome remains exposed to the air and sun. This exposure is important for the rhizome to dry quickly after watering and prevent rot. If planting multiple irises, larger bearded irises require 6 to 9 inches between rhizomes to prevent overcrowding. Gently firm the soil around the roots and water thoroughly to settle the soil and eliminate air pockets.
Essential Care After Planting
Container-grown irises require more attentive watering because the restricted volume of soil dries out faster. During the active growth and blooming season, keep the soil consistently moist but never soggy. Check the top two to three inches of the potting mix before watering; if it is dry, water thoroughly until it runs out of the drainage holes. Allowing the top layer of soil to dry slightly between waterings is important, as overwatering is a primary cause of rhizome rot.
Irises should be placed in a location that receives at least six hours of direct sunlight daily during the growing season. This high light exposure is necessary for the plant to produce the energy required for robust flowering. Since containers lose nutrients more quickly than garden beds, fertilization is necessary. Apply a balanced, slow-release fertilizer at the beginning of the growing season for sustained nutrition, or use a liquid fertilizer every few weeks.
Overwintering Protection
The most specialized aspect of care is overwintering, as container soil is exposed to freezing temperatures from all sides and lacks the insulating properties of the surrounding ground. In colder climates where temperatures consistently drop below 25 degrees Fahrenheit, the pots must be protected.
One effective method is to bury the containers up to their rim in the ground in a sheltered spot, such as near a house foundation. Then cover the soil surface with a thick layer of mulch or straw. Alternatively, pots can be moved to an unheated garage, shed, or cold frame to keep the soil temperature cold but above freezing. If moved indoors, the location must remain unheated to ensure the plant experiences the necessary period of winter chill required for future blooming.
For large containers that cannot be moved, wrapping the pot in layers of burlap or horticultural fabric provides insulation against the cold. This protection is necessary for the rhizomes or bulbs to survive the winter and return to bloom the following spring.