Thriving in sunny locations in any fertile but well-drained soil, a butterfly bush (Buddleja davidii) may be grown in a container. Since the shrub is fast growing and often matures 5 to 10 feet tall and wide, it's suitable to grow only for a short time in a container. The larger the container the better, so its roots enjoy ample room to develop and support the production of branches with flowers.
A young butterfly bush will thrive in a container setting for one growing season. After that, the roots will likely outgrown the soil volume in the pot and suffer the following year. For example, a butterfly bush that is purchased in a 10-inch diameter container, also referred to as a 3-gallon pot, will prosper if transplanted into a larger container that's at least 24 inches in diameter and hold at least 10 gallons of soil. Expect to transplant the shrub into the ground in the second year for it to continue to thrive.
Not all butterfly bushes are genetically equal. A wide array of cultivars exist that display different colored flowers and reach different mature sizes. If you choose to grow a butterfly bush in a container on the patio to attract butterflies, you should search for a dwarf or small-sized cultivar, rather than one that reaches 6 to 8 feet tall. Petite Plum, Petite Indigo/Nanho Blue, Petite Snow, Peacock, Nanho White and Nanho Purple are varieties that mature 4 to 5 feet tall and wide. The hybrid selection Blue Chip, marketed by its trademark name Lo & Behold, may be best suited for long-term container culture since it matures only 2 to 3 feet tall and wide.
Growing Plants in Containers
Gardeners choosing to plant butterfly bushes in large containers need to plan for extra watering, fertilizing and potential plant wilt in summer. The container needs to provide good drainage with multiple holes in the bottom, otherwise roots will suffocate and rot. Butterfly bushes need lots of sun. The full sun exposures encourage flowering, but the heat from the sunlight on the above-ground container causes the soil to dry out more quickly. Thus, more frequent watering on hot days is needed to prevent wilting. Do not use topsoil in containers as it will harden and compact; use a porous peat-based potting mix.
With a butterfly bush growing in a container, both summer heat and winter cold will penetrate into the soil and affect plant roots. In the northern U.S., the summer may prove the perfect temperature for the plant, but winters too cold for the normally hardy butterfly bush to survive. Insulate the container with straw or sink it into the ground to protect the roots over winter. Conversely, in the South, the winters are mild, but the long hot summers and intense sunlight may require additional watering or relocating the container to partial shade to keep the bush vibrant.