Gardenia Grow Guide
The iconic gardenia: Milky white flowers with an intoxicating fragrance, backed up by bright, shiny, evergreen foliage. The South’s most beloved shrub, the gardenia is a stand up specimen in all seasons. Unlike many flowering shrubs that bloom all at once and it’s over for the year, gardenias bloom intermittently from mid spring until autumn. If you live in a warm climate (within USDA zones 7 through 11), you should definitely have a gardenia (or several!) in your landscape.
Perfect Plants offers four gardenia varieties ranging from the miniature ‘Radicans’ gardenia that can be kept under three feet tall to the standard sized ‘August Beauty’ and ‘Frostproof’ varieties that grow to five or six feet in height. Gardenias are subtropical plants, best adapted to warm, humid climates, such as in the American South. Most gardenias are hardy only to zone 8, but ‘Frostproof’ and ‘Kleims Hardy’ can tolerate zone 7 winters.
You will want your gardenia located where the rich perfume of her blossoms can be appreciated: Near an entranceway, along a path, under a window, or by the pool.
Gardenias can suffer in full midday sun, especially in the warmer climates of zones 9-11, so choose a site that gets some afternoon shade. A site that is open to the north or east will get bright morning light but won’t be in full sun as would a site facing south or west. In zone 7, full sun and a southern exposure are desirable.
Gardenias need a slightly acidic soil. A pH of 5.0 to 6.0 is ideal. You should test the soil acidity with one of those pH kits available at garden centers. Note that the soil close to a house’s foundation will likely have a higher pH than the rest of the yard due to the leaching of calcium compounds from the concrete block. So, check your soil pH in several places before deciding on the best location.
If your soil pH is between 6.5 and 7.0, you can lower it by adding granular sulfur or iron sulfate. Work the sulfur into the soil about 8” deep. See the accompanying table for amounts to use. If possible, you should get the soil pH corrected at least 6-9 months before planting your gardenia.
If your soil has a pH greater than 7.0, we recommend against trying to correct it for acid loving plants. Better to select a substitute shrub that is already adapted to your particular soil.
To lower the pH of a typical loamy soil to 5.5:
8” into the soil
8” into the soil
|7.0||3.5 lbs/100 sq ft||21 lbs/100 sq ft|
|6.5||2.5 lbs/100 sq ft||14 lbs/100 sq ft|
If your soil is clayey and poorly drained, gardenias will not do well. They simply do not tolerate wet feet. To test if the soil is well drained enough, dig a hole 6” deep and 6” across, and fill it with water. If the water has not drained from the hole within three hours, the soil is too poorly drained for gardenias.
The ideal soil for a gardenia is a well drained, slightly acidic, sandy loam that is rich with organics.
The best time for planting any new shrub is spring, before it gets too hot, but still allowing a whole growing season to get established before winter.
Before starting, thoroughly water the soil in the nursery pot, then place the pot on its side and slide the root ball out. If the plant is stuck, you can slip a long-bladed knife around the inside edge to loosen it. Gently loosen some of the roots along the sides and bottom of the root mass, and pull them outward so they are not encircling the root mass. It shouldn’t be necessary to prune any of the roots unless they are wound around the circumference of the pot. In that case the offending roots should be shortened so that when they are in the ground they will grow outward and not continue growing in a circle.
Mound up some soil in the middle of the hole, 3-6” high, and place the center of the gardenia’s root mass on top of the mound, spreading roots out all around the hole. Backfill until the stem is at the same level it was in the original nursery pot, never lower. Do not add any fertilizer or amendments to the soil. You may have to pull the plant up as you backfill. Too shallow is better than too deep. When the hole is half filled, give it and the roots a good soaking of water. When the water has drained, readjust the depth of the stem if necessary and finish filling in the hole. Gently tamp the soil down with your hands.
Build a 3-6 inch high dike of soil on the surface around the outside of the root zone. This will help impound water over the roots as it sinks into the soil. Water thoroughly. Spread an organic mulch 3-6 inches deep over the root zone and beyond to help hold in soil moisture and prevent weed growth. You can use hay, straw, leaves, pine needles, bark or wood chips, grass clippings, or compost. Do not use mushroom compost as this contains lime and can raise the pH. Do not fertilize at this time.
Keep your gardenia well watered during its first growing season. If planted in the fall or winter, you can water once every week or two. Planted during the springtime growing season, they should get watered every day or two for three or four months. If you’re having a dry spell, or your soil is very sandy, you should water every day for the first three or four months. The most common reason for any newly planted shrub to die is lack of enough water.
Gardenias need about an inch of water, either from rainfall or irrigation, per week. Renew the mulch layer as needed to protect the roots from drying out, freezing, or overheating, and to smother weeds. Gardenias have shallow roots, so avoid cultivating around them. Instead, hand pull weeds that are not smothered with mulch.
Use an organic mulch that will decompose and add nutrients to the soil when it does. Try to maintain a mulch layer 3-6 inches deep around the gardenia at all times, but keep it a couple inches away from the trunk itself.
Fertilize gardenias monthly during the growing season (not in fall or winter) with a balanced fertilizer formulated for acid loving plants. Follow label directions and be careful to not over-fertilize.
You can encourage more flowering if you deadhead spent blossoms. Prune gardenia bushes in the dormant season to maintain the desired size and a pleasing shape.
Sooty mold: A grayish fuzzy looking mold will sometimes appear on the leaves. This mold is actually growing on the excrement of any of several plant sucking insects. Sooty mold is rarely a serious problem, but if the aphid or scale insects are especially troublesome, they can be killed by spraying with insecticidal soap.
Buds dropping: If a gardenia doesn’t get enough water (about an inch per week) during the blooming period it may drop flower buds before they ever open.
Leaves turning yellow: If the soil is not well drained enough, and the roots stay wet for too long, leaves can turn yellow and eventually drop. Another cause of yellowing leaves is iron deficiency. The soil must be slightly acidic for the successful uptake of iron. You can try to adjust the soil pH with a sulfur-containing fertilizer formulated for acid loving plants. For a short term cure, spray an iron foliar fertilizer on the leaves.