Gardenias are one of the most popular and rewarding garden shrubs to grow in temperate and subtropical gardens. Their heady fragrance, masses of beautiful cream flowers from spring to autumn and glossy green leaves make a highly desirable combination for gardens, hedges or pots.

In early spring, though, gardenias can be a worry. By the end of winter, they are often looking miserable with yellow leaves and no flowers – or worse, buds that are brown and dropping.

Most gardeners have heard somewhere along the garden grapevine that gardenias need a dose of Epsom salts in spring. While this won’t hurt them, magnesium deficiency (which is what is treated with Epsom salts) is a very minor disorder.

The key to understanding how to improve the look of gardenias in early spring is to know the conditions they enjoy. Gardenias are subtropical shrubs and are related to citrus. They grow naturally in areas with mild winters and warm, moist summers.

In most parts of southern Australia, winters vary from mild to cold and even frosty. When soils are cold, gardenias wish they could relocate to Cairns or somewhere tropical. In these cold and often dry conditions, they hunker down and stop taking up nutrients. This is what leads to yellowing leaves.

With the arrival of spring, day temperatures begin to rise, but soil warming is slow. Gardenias take time to get the nutrients they need to return to their lush, green state. By late spring, however, the warm soils, balmy days and higher humidity levels see most gardenias looking far better.

Tips to boost your gardenias

  • Liquid feed: In late winter and early spring, apply a liquid fertiliser for flowers - we love Sudden Impact for Roses liquid, which is great for all flowering plants - not just roses! Repeat in a fortnight. If yellow leaves persist, or leaves are looking pale with darker veins, apply Yates Iron Chelate Liquid (follow the instructions on the container) which will help to correct iron deficiency and encourage greener growth.
  • Slow release feed: In addition to the liquid food, scatter slow-release fertiliser around your plants. There are plenty of special formulations for gardenias on the market, but our favourite is Kahoona. Alternatively, you can use any product that's formulated for flowering plants or citrus. This fertiliser will kick in to feed the plant as conditions warm. Feed again in summer and autumn.
  • Water: If the soil is dry, water gardenias well making sure that the water is soaking in around the roots. Water regularly when conditions are dry. If soils are hard to wet, mix a soil wetting agent into the watering can - Wettasoil is a great option for this.
  • Add organic matter: Spread a few spades of composted cow manure or compost under the plants as mulch – organic matter helps improve soil condition, which leads to better growth.
  • Remove old buds: Buds formed in late autumn often fail to open. Remove these to make way for new flowers.
  • Check for pests: Check for waxy brown or white scale on the backs of leaves and on stems. Ants on the plant or a skin of black sooty mould on the leaves indicate the plant has scale. Spray with horticultural oil.
  • Repot: Potted gardenias that have been in the same pot for two or three years can be repotted in spring into a larger pot with fresh, good quality potting mix. For the happiest gardenias, we suggest you choose a premium mix that's specially formulated for gardenias, such as Supersoil Professional Gardenia, Camellia and Azalea Potting and Planting Mix.
  • Chewed buds: Weevils hide in the soil and feed on new buds and leaves. Use a torch to check plants at night and squash any found. With good feeding and regular watering, most plants will outgrow the damage.
  • Pruning: If pruning is needed to tidy or shape the plant, it can be done at any stage during the warmer months. The gardenia will quickly put on new growth, but remember - pruning delays flowering.