How to grow gardenias

What are gardenias?

Gardenias (Gardenia jasminoides AGM) are mainly grown as flowering houseplants in the UK, filling our homes with their heady, jasmine-like scent. They are tender shrubs with glossy evergreen leaves and large, creamy-white summer flowers. They’re usually grown indoors all year round, but can be moved outdoors during the warmest months.

Gardenias need acidic compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. , humidity

The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting. , warmth and bright light, but not direct sun. Keep the compost moist but not waterlogged

Describes soil or potting compost that is saturated with water. The water displaces air from the spaces between soil particles and plant roots can literally drown, unless they are adapted to growing in waterlogged conditions. Waterlogging is common on poorly drained soil or when heavy soil is compacted. . Some care and attention is required to get the growing conditions right. For that reason, gardenias are often treated as short-lived plants. It can be tricky to keep them going long term. After a few years, flowering tends to decline, but it’s easy to take cuttings, to grow your own replacements.

Buying gardenias

The most popular species, Gardenia jasminoides AGM, is widely available as a houseplant, and there are several cultivars to choose from too, including ‘Kleim’s Hardy’ and ‘Crown Jewel’. Look for them in the houseplants section of garden centres and online plant suppliers. They are mainly available in spring and summer, usually in full flower to provide instant impact in your home.

• Gardenias need re-potting regularly, ideally every spring, as they dislike congested roots
• Move them into a container that is only slightly larger, to avoid problems with overpotting
• Use peat-free ericaceous compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. (for acid-loving plants), which is widely available in garden centres
• If you can’t re-pot, then top-dress in spring by scraping off the top 5cm (2in) of compost, and replacing it with fresh peat-free ericaceous compost

Repotting is easy – just follow our guides:

How to repot a plant

Peat-free compost choices

Location

Position gardenias in a warm, bright spot, out of direct sun. A west-facing windowsill is ideal. Strong, hot sun can scorch the leaves or cause them to wilt. Ensure there is some air-flow too, but no cold draughts.

In winter, move your gardenia to a south-facing windowsill, to get as much light as possible during the shorter days.

See our quick video guide:

You can also move gardenias outdoors for the summer – give them a warm, sheltered spot in partial shade. In a porch, doorway or beside a seating area would be ideal, so you can enjoy their fragrant flowers to the full. Some cultivars are said to be relatively hardy, such as ‘Kleim’s Hardy’ and ‘Crown Jewel’. However, it’s still advisable to keep them frost free

Frost-free environments, such as a cool greenhouse or conservatory, have a nighttime minimum of 4°C (39°F). This is ideal for plants tolerant of low temperatures, but will not survive being frozen, such as tender plants being overwintered including pelargoniums; frost-tender rooted cuttings such as penstemon; and bedding plants in spring. by putting them in a conservatory, sheltered porch or similar over winter.

Temperature

Gardenias like temperatures of 21–24°C (70–75°F) during the day, and a slightly cooler 15–18°C (59–65°F) at night. However, large fluctuations can damage the flower buds

A bud is a small, undeveloped shoot that contains the potential for new growth. Buds are typically found on stems, where they can be apical (found at the tip) or axillary (found between leaf axils) and may develop into leaves, shoots or flowers. . They prefer a winter temperature of 16°C (61°F), but can cope with 10–15°C (50–59°F).

If you put them outside in summer, acclimatise them gradually to outdoor conditions by hardening off. Then be sure to bring them in before night temperatures fall below 10°C (50°F), even the cultivars that are said to be more cold tolerant.

Watering

• Through spring and summer, keep the compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. constantly moist, but not saturated
• In winter, when the plant isn’t growing, reduce watering, but don’t let the compost dry out
• Use rainwater where possible, especially in hard water areas, to ensure the potting compost stays acidic. Let the water reach room temperature before applying

Humidity

Gardenias like high and uniform humidity

The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting. , so stand the container in a tray of damp gravel. Mist the leaves frequently in hot weather, but not when in flower, as water on the petals can discolour them.

Feeding

Gardenias are hungry plants, so give them a high nitrogen liquid feed every week in spring and summer. Then in winter, feed with a balanced fertiliser with trace elements every five to six weeks.

Deadheading

Remove fading flowers regularly to encourage more to form – see our guide to deadheading.

Keep gardenias in good shape by lightly pruning in February or March – see our guide to light pruning.

Gardenias are easy to grow from cuttings. And it’s a good idea to take cuttings

A method of growing new plants from parts of an existing plant, such as sections of root, stem, leaf or bud. When prepared correctly and planted in the right conditions, they can produce roots and eventually become independent plants. There is a wide range of different methods for taking cuttings, depending on the plant and time of year. annually, as flowering tends to reduce after a few years, so plants need replacing.

You can take:

• softwood cuttings in late winter or early spring
• semi-ripe cuttings in summer – heel cuttings are often especially successful

Once rooted, move them into individual pots of peat-free ericaceous compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. . Re-pot annually as they grow, to ensure the roots don’t become congested.

Gardenias require specific growing conditions and can develop various symptoms if their needs aren’t being met. These include:

• Yellowing leaves – often on new growth and usually due to overwatering or iron deficiency. Too much water can damage the roots, leading to yellowing foliage. If overwatering isn’t to blame, then iron deficiency is likely, particularly in hard water areas. Apply chelated (sequestered) iron – and re-apply regularly if you’re using hard water. See our guide to leaf discoloration
• Browning leaves –too little water can cause leaves to turn brown at the tips and edges
• Yellow shoots (chlorosis)–this, and slow growth, are usually caused by poor light and low temperatures. Move the plant to a warmer, brighter spot
• No flowers – this can be due to hot nights, 18°C (65°F) or above, and dry air. Move the plant to a cooler spot and increase humidity
• Bud
  A bud is a small, undeveloped shoot that contains the potential for new growth. Buds are typically found on stems, where they can be apical (found at the tip) or axillary (found between leaf axils) and may develop into leaves, shoots or flowers. drop – usually the result of extreme or fluctuating temperatures, too much or too little water, or irregular watering. Move the plant to a location that can be kept at a constant temperature. Keep the compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. consistently damp in spring and summer, neither waterlogged
  Describes soil or potting compost that is saturated with water. The water displaces air from the spaces between soil particles and plant roots can literally drown, unless they are adapted to growing in waterlogged conditions. Waterlogging is common on poorly drained soil or when heavy soil is compacted. nor dried out
• Wilting leaves, even with moist compost – this indicates that moisture is being lost through the leaves more rapidly than it can be taken up by the roots. Move to a shadier position and mist the leaves several times a day with rainwater until the plant has recovered. Stand it in a tray of damp gravel in spring and summer to raise humidity

Also check plants regularly for sap

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding. -feeding insects, including red spider mites, mealybugs, scale insects and aphids.

For more tips, see the following guides:

How to help a poorly houseplant

Leaf damage on houseplants