It is a good idea to deadhead gardenias. Removing spent blooms prevents the plant from setting seed. Deadhead a gardenia after the blooms wilt and it will direct its energy into producing flowers allowing you to enjoy more of the wonderful blooms. Remove old flowers and the shrub will look more attractive, too.
As with most flowering plants, the best time of year to prune a Gardenia is just after flowering. Most Gardenias flower in spring and summer, so the end of summer or early autumn is generally best.
Feeding and mulching Gardenias are fed during the growing season from spring to autumn with a complete fertiliser such as Seasol plus Nutrients Roses & Flowers. Water it in well after application. Plants also benefit from liquid feed such as PowerFeed PRO SERIES for Roses & Flowers during the growing season.
Young gardenia leaves turning yellow is likely from low iron. All can be fixed by giving your gardenia a dose of an acidic nitrogen fertilizer containing micronutrients. Once your gardenia leaves are green again, use the fertilizer twice a month from early spring to late summer.
1. A simple deadhead involves pinching off the flower, if you can do this with your fingers; or snipping off the flowerhead and a little bit of stem. 2. For shrubs with thicker stems, it's often a good idea to cut back to just above what is called a node – the point where the leaves come out of the stem.
If leaves yellow on your gardenias into the warmer months, it's likely to be a lack of iron and/or magnesium. Magnesium deficiency first affects old leaves. Sprinkle a teaspoon of Epsom salts around the plant and water in. Iron deficiency first affects new leaves.
Pruning. The best way to maintain bushy growth is to prune the flowers with a 10-15cm stem – perfect for a vase. If the shrub has been neglected and become straggly now is the time for a renovation prune. Remove up to 60 per cent of the shrub, leaving a few leaves on the lower third of the bush to aid recovery.
Gardenias will appreciate coffee grounds mixed into the soil as well. Since they are rich in nitrogen, magnesium, and potassium, spent coffee grounds are oftentimes a more favorable gardenia fertilizer than commercially available Fertilizers.
Gardenias usually bud with their sweet-smelling flowers in spring and summer, although some varieties will bloom again in the fall. Not to fret when they're not blooming, the dark green waxy leaves are still a garden delight.
Low on Magnesium
If your gardenia needs magnesium, this will cause the leaves to turn yellow. You can remedy this with a fertilizer high in magnesium, or you can add some Epsom salts to your soil. Mix one teaspoon to one gallon of water and apply every two to four weeks.
Gardenias usually perform best in full sun but may appreciate shade during the hottest part of the day in the warmest parts of their hardiness range. They seem to grow best in humid areas and don't tolerate drought or arid conditions well.
Gardenias do not need to be pruned every year. Many gardeners trim their shrubs every other year or even every three years to keep their size and shape in check. This can be a matter of personal choice and also garden space and design. You may want to keep your shrubs more compact in size.
Potting and Repotting Gardenia
Gardenias do well outdoors in containers and can even be pruned into topiaries. For first-time potting, use a container slightly larger than the one from the nursery. Like growing gardenias in the ground, acidic, well-draining, evenly moist soil is required.
Gardenias need a full sun to part shade spot - depending on the variety you've chosen - all varieties will appreciate protection from hot afternoon sun and frosts. Gardenias prefer a moist, but free draining soil that's slightly acidic.
When you see an entirely yellow leaf, you should remove it from your plant using a sterile cutting tool. Removing the leaf will let the plant focus its nutrients on healthy leaves. A yellow leaf has lost its chlorophyll (pigment) and it can't turn green again even after you correct the problem.
High Soil pH
As a acid-loving plant gardenia grow best in soil with a pH of 5.0 to 6.0. but when the pH goes past 6.5, gardenia leaves will become yellow (chlorotic) due to iron deficiency caused by alkaline soils.
If you have an overwatered Gardenia, you'll see the leaves turn yellow and start drooping. You'll notice that it affects the older, lower leaves first before spreading upwards. Eventually, the leaves will drop off, even if your soil has moisture. New buds may appear, but they will die soon after that.