Can Annual Plants Be Grown Indoors?
Annual plants, by definition, are those that only grow for one growing season. Once they flower and set seed, they die. They’re traditionally grown in outdoor gardens for the addition of colorful flowers all summer; they don’t make long-lived plants for growing indoors.
Learning Objectives
- What is an annual plant
- True annual plants vs mislabeled perennials
- Challenges of growing annual plants indoors
- Choosing annual plants to grow indoors
Table of Contents
What Is an Annual Plant
The botanical definition of an annual plant grows, flowers, sets seed, and then dies all in one growing season. Annuals are most often grown in outdoor gardens for their colorful show of summer flowers or as edible crops.
The label “annual” on plants sold in the spring at garden centers in temperate growing zones can sometimes be misleading. Some of the summer-flowering plants are labelled as annuals when in fact, they’re not. These plants are, botanically speaking, perennials; in their frost-free native habitats they grow back year after year. These mislabeled perennials are often sold and treated as garden annuals in cooler plant hardiness zones where they die off after the first heavy frost. They’re grown for their summer display of flowers or bright-colored foliage and then discarded at the end of the season.
This is why knowing a plant’s actual hardiness zone is important. A botanically perennial plant native to zones 9-11, for example, may be grown just for the summer in colder regions like zones 4-5 and then die off with the arrival of the first frost. It is treated like an annual when, in fact, it’s a perennial that would survive several years in frost-free zones.
The Challenges of Growing Annuals Indoors
Annual plants, by definition, die after flowering and setting seed, so they generally make short-lived houseplants. It’s impossible to fight a plant’s genetics and have an annual grow indefinitely. However, there are ways to extend an annual plant’s lifespan for a little more enjoyment.
True annuals are usually grown in the outdoor garden for their beautiful flowers throughout the summer growing season until first frost. Some can also be grown indoors, where their flowering season can be extended a bit by the warm indoor temperatures with adequate light levels (often with the use of plant lights). However, even with plenty of warmth and light, true annual plants will be short-lived indoors.
How to Choose Annuals to Grow Indoors
When choosing annual plants for an indoor garden, it’s important to know which ones are true annuals and which ones are just treated like annuals; which ones will be short-lived and which ones are actually “mislabeled perennials” that could be maintained indoors for several years.
The good news is, many of the traditional favorite summer-flowering annuals for the outdoor garden are actually “mislabelled perennials” that could grow indefinitely, including zonal geraniums (Pelargoniums), petunias, impatiens and coleus. In growing zones where temperatures stay consistently above freezing, they can grow for several years. These are the flowering “annual” plants to grow indoors if you want something long-lived.
These true perennials can be grown successfully as indoor garden plants when given the right growing conditions. Most will require at least 6 hours of direct sunlight to flower well, while others can tolerate a little shade. It’s also important to keep in mind that most of them will go through a dormant period (usually winter) when the plant takes a rest from flowering for several weeks.
Following is a list of a few flowering perennials traditionally grown outdoors as annuals that you could grow and enjoy indoors. NOTE: If you have small children or pets, always research the toxicity of any plant you want to grow indoors.
Nasturtiums (Tropaeolum majus)
Nasturtiums are probably one of the most familiar summer flowering “annuals,” but they are, in fact, perennials native to Central and South America. They are garden perennials in hardiness zones 9-11 and treated as annuals elsewhere. They have flattened trumpet-shaped flowers in vibrant colors of red, yellow, or orange. Some varieties are trailing while others grow in a low mound. All plant parts are edible; the leaves and flowers have a peppery flavor like watercress, and the unripened green seed pods have a citrusy peppery flavor. Seed pods can be pickled as a substitute for capers, earning the nickname “poor man’s capers.”
Polka dot plant (Hypoestes phyllostachya)
Polka dot plant is popular for its rich green leaves covered in bright pink or white spots like it was attacked with a can of spray paint. It’s native to tropical rainforests where it grows in dappled sun or bright shade. As a houseplant, it prefers bright indirect light – direct sun will fade its colors – and high humidity. It’s a good choice for a bathroom with bright natural light. These plants grow 1-2 feet (30-60 cm) tall and wide. It can live for a few years, but once it flowers, it dies soon after. To extend the life of your Polka dot plant, cut out the flower stalk as soon as it appears.
Lantana (Lantana camara)
Lantana is a longtime favorite in the outdoor garden for its brightly-colored, long-lasting flowers. They have flat clusters of small flowers in colors ranging from pinks, yellow, orange, white, and purple. As an indoor plant, given the right conditions and care, lantana will flower almost year-round. Note: Lantana is slightly toxic if ingested, and the leaves may cause skin irritation.
Coleus
Coleus plants are grown for their richly colored foliage that comes in shades of bright or dark green, yellow, orange, purple, and pink, usually with many colors on one plant. They like bright but not strong direct sunlight. A north or east-facing windowsill would suit them well. They can grow 2-3 feet (60-90 cm) tall but over time, older plants become leggy (spindly). To keep plants nice and full, pinch back the growing tips to encourage denser, bushier growth. Coleus sometimes flowers indoors but will die soon after. Cut back any flower stalks as soon as they appear to extend the life of your plant.
Petunias
These mounding or trailing favorites need at least 6 hours of direct sunlight daily to flower well. A south or west-facing window is best. They can also be grown under plant lights, especially in winter to extend the bloom period. They will grow sparse and leggy with few flowers if they don’t get enough light. Spent flowers should be pinched off to encourage further flowering. The growing tips should be pinched back periodically to encourage bushier growth. During lower winter-light conditions, petunias will go dormant and reduce or stop flowering.
Bedding impatiens, Busy Lizzie (Impatiens walleriana)
Impatiens are a pillar of the summer outdoor shade garden. Treated as an annual in temperate growing zones, it is actually a perennial native to eastern Africa. It adds pops of color with flowers in shades of red, pink, white, or light purple. It is an easy-care houseplant that likes bright indirect light (no direct sunlight) or bright shade and high humidity. Impatiens grow to about 12 inches (30 cm) tall. To keep plants from getting too leggy and to encourage continued flowering, the growing tips should be pinched back regularly during the growing season (spring through fall). Spent flowers should also be pinched off before a seed head develops, to encourage more flowering. The plants will go dormant and reduce flower production during low-light winter months.
Zonal Geraniums (Pelargonium x hortorum)
Zonal Geraniums are another favorite for summer outdoor gardens in temperate growing zones. Treated as an annual, they are often discarded at the end of the summer with the arrival of fall frosts, but they are actually perennials native to subtropical regions including South Africa. Their flowers come in colors from white, red, pink to salmon orange. They are relatively easy-care houseplants that like bright indirect light. An east or west-facing windowsill is a good spot. They’ll flower continuously spring through fall, and then reduce flowering with the lower winter light levels. (NOTE: While the Pelargoniums generally go by the common name geraniums, they are not to be confused with plants of the true Geranium genus, often referred to as cranesbills. These perennials are usually grown in outdoor gardens where they die back when temperatures drop below freezing)
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