How to Grow Outdoor Perennial Plants Indoors
In the world of gardeners, the term “perennial plants” is generally used for long-lived plants grown in an outdoor garden. However, tropical plants grown as houseplants in temperate regions are also, botanically speaking, perennial plants that survive for several years in their native habitat. For the discussion of choosing plants for an indoor garden, we’ll use the term “outdoor perennials” to distinguish those usually grown in an outdoor garden from tropicals traditionally grown indoors as houseplants.
Learning Objectives
- What is an outdoor perennial (trees, shrubs, and perennials)
- Challenges of growing outdoor perennials indoors
- Choosing outdoor perennial plants to grow indoors
Table of Contents
What Is an Outdoor Perennial Plant?
The botanical definition of a perennial plant survives for more than two years. Some are described as evergreen (they’re green through all seasons), and others are deciduous (they lose their leaves in the fall/winter). The term “herbaceous” is used to describe those whose top growth (aboveground) dies back for winter and then sprouts anew in the spring.
Outdoor perennials are plants that are usually grown in an outdoor garden rather than indoors as a houseplant. The distinction is important when it comes to choosing plants to grow indoors.
Outdoor perennials include trees, shrubs, and smaller evergreen or herbaceous plants like ferns and Shasta daisies. These smaller plants are collectively referred to as perennials in the horticultural trade. Spring and summer-flowering bulbs such as tulips, daffodils, and lilies are also perennial; they die back after flowering – or at the end of the summer – and regrow the following year.
Outdoor perennials need specific growing conditions to thrive, and most go through a dormant period, meaning their growth slows – or the top growth dies back completely – for several months. Some plants go dormant with the arrival of cooler temperatures of fall through winter, while others grow best in cooler spring conditions and go dormant in the summer heat. These growth habits are important to understand when considering perennials for an indoor garden.
The Challenges of Growing Outdoor Perennials Indoors
Just about any plant can be grown in a container, but not all plants can be grown successfully in a container indoors. Perennials in the outdoor garden grow – and flower – in response to seasonal changes in air temperature as well as day length (a response known as photoperiodism) and intensity of sunlight. It can be challenging to replicate these seasonal changes indoors.
Outdoor perennials’ growth cycles respond to the seasonal changes in growing conditions. As the days grow shorter and cooler in the fall, most perennials go into a dormant phase when top growth slows down, then stops – or dies back completely – for the winter (roots underground never go completely dormant)
Many flowering shrubs, conifer trees, and herbaceous flowering perennials need a chilling period to stimulate the development of flower buds or growth buds for the following spring. This is a natural process known as “vernalization.” The number of weeks and exact temperature required for vernalization differ depending on the variety of plant.
These seasonal growth cycles and the need for vernalization mean that not all outdoor perennials will perform well indoors where the growing conditions remain warm and relatively consistent. Evergreen flowering shrubs, for example, may have healthy greenery but won’t produce flowers. Coniferous trees, such as many species of pine, need a period of winter chill for the development of new growth buds, and may not grow well indoors.
Light levels can be simulated artificially with plant lights, but it can be difficult to reproduce the chilling temperatures – just a few degrees above freezing – needed for vernalization.
Spring and summer-flowering bulbs are also perennials that require vernalization to flower. When these colorful beauties are available from florists in the dead of winter, they have been put through an artificial vernalization process in special facilities, and then grown in greenhouses to bring them into flower. Vernalization under artificial conditions is a process known as “forcing” because the plants are being forced to flower on a different schedule than they would if grown naturally outdoors.
Garden centers and florists often sell unplanted bulbs such as hyacinths or paperwhites labelled “forced” or “prepared,” which means the bulbs have already undergone a cold treatment and will flower once planted. These are often grown to root in water rather than planted in soil, and then discarded after flowering. Even the seasonal favorite amaryllis bulbs have undergone a forcing treatment to prepare them for market.
It is possible to force flowering bulbs at home, but it takes patience and the appropriate available space
Growth cycles aside, some outdoor perennials will simply get too big to be maintained indefinitely in a container, indoors or outside. Plants grown in containers will naturally stay smaller than if grown in the ground outdoors because of limited root space, but only to a point. If a shrub or tree will reach more than about 10 feet (3 m) tall at maturity, it’s not a good candidate for growing indoors. The only exception to this rule is the ancient Japanese tradition of bonsai. Bonsai involves growing dwarfed specimens of trees or shrubs that would otherwise grow much larger in the outdoor landscape. It involves special planting and meticulous maintenance techniques, and is an art that takes several years to perfect
Flowering Perennials Purchased from a Florist
Outdoor flowering perennials are sometimes available “out of season” through florists or where tropical houseplants are sold. These flowering perennials – often sold for holidays like Christmas, Valentine’s or Easter – have undergone an artificial vernalization process (they’ve been “forced”) and then grown in greenhouses so they flower at a different time of year than they would when growing in an outdoor garden (i.e. they’re out of season). Once these florist’s perennials have finished flowering, their foliage might continue to grow indoors, but they won’t rebloom without another artificially-induced vernalization cycle.
Florist’s perennials can be confusing because wide varieties of these “out of season” flowering plants are also sold at garden centres for planting in the outdoor garden. If you purchase them at a garden centre in the spring to grow indoors as a houseplant, they would probably bloom that first season, since they’ve undergone a natural vernalization process before arriving for sale at the garden centre. However, they wouldn’t bloom again if kept indoors.
The out-of-season bloomers sold for enjoying indoors are usually labelled as “Florist’s” perennials to differentiate them from the same perennials sold for an outdoor garden. Examples include florist’s hydrangea, azalea and chrysanthemums. If you purchase florist’s perennials, be aware that they will be short-lived houseplants. They won’t rebloom unless you have the patience and space to provide them with the required vernalization period – which varies from plant to plant. Temperatures required for vernalization are usually in the range of 40-50 F (4-10 C) for several weeks or months.
The other perennial often sold as a short-lived houseplant is the florist’s miniature rose. These are marketed for Valentine’s Day or Mother’s Day but are often available all year. Most of these florist’s mini roses will be short-lived houseplants without some challenging after-bloom care, but not because they need vernalization. Florist’s miniature roses are generally grown as cuttings in greenhouses under perfect growing conditions and forced to the flowering stage for market. Often 3-4 young cuttings are planted into one small pot to give the effect of a single bushy plant full of buds. Once they’ve finished flowering, the stressed young cuttings are unlikely to bloom again unless they are repotted into a larger container and given adequate light and growing conditions to mature. It may be several months before they flower again, if at all.
Indoor growing conditions vary widely from those in the outdoor garden, and it can be challenging to recreate the exact growing conditions that many outdoor perennials are adapted to; light levels, temperature, and humidity all play a role in plant health. As a result, outdoor perennials grown indoors tend to be under some degree of stress much of the time. Just like we can be more prone to catching a cold when we’re tired or stressed, plants are more susceptible to attack by insects or disease. It’s important to check your houseplants, especially outdoor perennials, regularly for any signs of pests or disease so you’re able to take action early, if needed.
How to Choose Outdoor Perennials to Grow Indoors
Not every outdoor perennial will make a good houseplant, so it’s important to do some research about a plant’s specific needs and lifecycle before bringing it home.
The outdoor perennials that tend to grow best indoors as long-lived houseplants are those that prefer shaded conditions in the outdoor garden, such as evergreen ferns or the Japanese laurel (Aucuba) shrub. The natural light indoors is less intense than sunlight outdoors, so these outdoor perennials can tolerate the lower light conditions indoors.
Perennials requiring full sun in the outdoor garden will usually need artificial lighting to grow well indoors. Other outdoor perennials to consider for indoors are those that don’t require vernalization to flower or set new growth buds. Without doing a lot of research, look for plants that are listed as hardy in USDA growing zones 7 or above; they’re adapted to conditions that don’t go far below freezing for an extended period and likely don’t need vernalization.
If you’re considering smaller perennial plants (i.e., under 3 feet or a meter tall), consider only evergreen varieties (they stay green all year). Plants described as herbaceous have topgrowth that dies back during a dormant period (usually in winter but occasionally in summer). That way you’ll have a houseplant you can enjoy all year.
The following list offers some examples of outdoor perennials that can be grown successfully indoors as houseplants. (NOTE: If you have small children or pets, always research the toxicity of any plant you want to grow indoors.)
Japanese laurel (Aucuba japonica)
Japanese laurel (or Gold Dust Plant) is a slow-growing evergreen shrub that adapts well to indoor conditions. This plant adds a splash of color with its glossy deep green leaves covered in bright yellow speckling. Indoor plants will grow up to 3 feet (90 cm) tall. They prefer bright filtered sunlight; an east-facing window with a couple of hours of morning sun would suit it well.
Roses (Rosa sp)
It’s possible to grow garden roses indoors but only if they’re given the right conditions, especially enough light. They need at least six hours of direct sun daily to grow well and produce flowers. A south or west-facing window is ideal, with daytime temperatures of 70 to 75 degrees F (21-24 C). There are some varieties that tolerate part shade in the outdoor garden; these will adapt better to the lower-light conditions indoors. It’s also important to keep in mind the ultimate size of the mature plant. Varieties that stay under 3-4 feet (90 – 120 cm) in height will be fine in a large container (20-24 inch diameter) and won’t take up too much space. Also look for varieties labelled “patio roses” as these have been bred for their more compact size and suitability for container growing. You’ll often find patio roses trained as standards (tall bare trunk with round bushy growth at the top.) These are a good size and tidy shape for growing indoors. Then there are the ever-popular miniature roses, so named because the plants stay small, and have smaller leaves and flowers than most other roses. For a long-lived plant, buy these at the garden centre, as opposed to “florist’s mini roses”
True jasmine (Jasminum sp)
There are several species of true jasmine (family Oleaceae), some of which can be grown as houseplants, including Common Jasmine (Jasminum officinale) and Pink Jasmine (Jasminum polyanthum). These are the varieties sold by florists as an indoor houseplant, with their vining stems trained around a wire frame. They all produce clusters of white star-shaped strongly-scented flowers, and Pink Jasmine has pink-tinged flower buds. They all grow best at temperatures in the range of 60 – 75 degrees F (16-24 degrees C) and are sensitive to low-humidity conditions. They need at least 6-8 hours of bright indirect sun to flower well or can be grown using plant lights.
Jasmines need a dormant period of cooler temperatures between 50 and 60 degrees F (10 – 16 degrees C) and long winter nights (in total darkness) to stimulate development of flower buds for the following spring. If you’d rather enjoy jasmine flowers all year, grow Arabian Jasmine (Jasminum sambac); it is an everblooming species that does not need a dormant period to set flower.
Star Jasmine (Trachelospermum jasminoides)
Star jasmine is not a true jasmine but is a similar-looking plant in the Apocynaceae family. It is an evergreen vine that produces clusters of small white wonderfully-scented flowers from early to late spring through to fall. It is fast-growing and will need a solid structure such as stakes or a trellis to support its woody self-twining vines. Star jasmine needs at least 6-8 hours of bright indirect sunlight to flower indoors. By a sunny window covered with a sheer curtain would be a good location.
Evergreen Ferns
Ferns are some of the best outdoor perennials for adapting to growth indoors, since they grow best in low-light conditions. Evergreen varieties won’t die back for the winter, so they provide you with indoor greenery all year. Garden ferns are known to prefer moist soil and humid conditions, which can sometimes be challenging to provide indoors. However, there are several varieties that are drought tolerant; these are the ones that grow best indoors. Examples of drought-tolerant evergreen varieties include Autumn Fern (Dryopteris erythrosora), Male Fern (Dryopteris filix-mas), Christmas Fern (Polystichum acrostichoides) or the larger specimen Western Sword fern (Polystichum munitum)
Wood sorrel, False Shamrock (Oxalis triangularis sp)
Oxalis isn’t a true shamrock plant; it gets its common name from its three-lobed leaves that look like shamrocks. They are bulbous plants (grow from bulbs) that don’t need vernalization to flower. There are several varieties of Oxalis, with foliage in shades of green, deep purple or a combination of both. The leaves and flowers respond to light levels, curling up in the dark and unfurling again at day break, a behavior known as nyctinasty. Oxalis grows to about 12 inches (30 cm) tall. The clumps will grow as wide as the container allows, up to 24 inches (60 cm). From early spring through fall, Oxalis bears delicate white, lavender or soft pink flowers on long slender flower stalks that grow up above the foliage. They need bright indirect light (direct sun will burn the leaves) and grow best in temperatures of 60-70 degrees F (15-21 degrees C). Keep them out of cold drafts or spots with drastic temperature fluctuations. It can tolerate short periods of drought but if allowed to dry out for too long, the plant will go dormant; the foliage will die back and regrow several months later.
Lavender (Lavandula spp)
Lavender isn’t a plant traditionally grown indoors, but it is possible. The challenge is to give it enough light to flower; in the outdoor garden lavender is a full-sun plant. Indoors it needs at least 6 hours of direct sunlight in a day, which can be provided in a south-facing window. It can also be grown under plant lights for at least 12 hours a day. Lavender is a Mediterranean plant, preferring low humidity, so it grows well indoors. In summer it prefers temperatures around 70 degrees F (21 C) and in the lower-light of winter months it prefers cooler temperatures around 60-65 (15-18 degrees C) during the day.
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