Here at Gardening Know How we get lots of questions, and our goal is to provide answers to those inquiries to the best of our knowledge. These may run the gamut of vegetable gardening to trees and shrubs, and anything or everything in between. Gardenias are popular shrubs grown both indoors and in the garden. The following information includes the 10 most commonly asked questions relating to gardenia plants.
Gardenias are notorious for getting yellow leaves and it can happen for many reasons. Yellow leaves normally signal that the plant is under some type of stress. In order to remedy the problem, you must first try to pinpoint the issue. Anything from poor drainage, root problems, high pH levels, or not enough nutrients can all lead to leaf yellowing in gardenia plants. Start by checking the plant’s soil. If it’s too wet, this could signal an issue with drainage or even overwatering. Testing the soil is another good idea to see what, if any, nutrients are missing or if the soil pH is too high. I would also check the plant for pests. A number of insects attack these plants, which can cause yellowing.
As long as temps don’t fall below 20 F. (-7 C.) for extended periods, gardenias can survive outdoors just fine. However, placing potted plants in a sheltered location will help protect them during any unusual cold spells. Also, in the event of heavy frost or freeze warnings, you may want to cover them. Most gardenias in winter cannot survive outside in areas that drop below 15 degrees F. (10 C.). If you live in an area that gets colder than this in the winter, you will need to bring the plant indoors. If it’s in the ground, dig it up and trim back the plant to help it adjust to a smaller root system. Then acclimate it for bringing in the house. Container plants should be acclimated.
First of all, these plants are somewhat finicky but given suitable growing conditions can make beautiful additions to the landscape. Gardenia shrubs are sensitive to cold, so if you’re in a cool climate, you may want to grow the plant indoors. That being said, in the garden the plant prefers moist, well-draining, acidic soil. Gardenias also enjoy areas of partial shade. Indoor plants, on the other hand, generally require bright light and high humidity. If you can provide these requirements, indoors or out, then caring for your plant shouldn’t be difficult. Watering varies, BUT you should be checking the soil on a weekly basis for indoor plants, watering only when the top is almost dry. Fertilize monthly with something specifically formulated for acid-loving plants.
It is recommended that you wait until after it blooms to prune gardenia plants so that you do not lose the flowers. If you prune at other times, you will reduce the number of blooms you get on the plant in the coming year, if at all. That being said, while it is typically recommended to prune gardenias after they bloom, it is permissible to do so after they suffer cold or frost damage. If another round of cold is imminent, though, you may wait until spring to cut back the plant. It will help protect the new growth should another freeze occur. Be aware that the buds will have been damaged and it is unlikely you will get flowers this year.
Most varieties bloom in early summer (mid- to late June) but when a gardenia fails to flower, it may need some coaxing. It may need more light or warmer temps to bloom faster. Try putting it in a brighter window or ensure that it’s not become too shaded outdoors. Also, don’t overwater. Too much water can reduce your blooms. You want the soil moist but not wet. Gardenias that have too little phosphorus will look lush but will lack flowers. Try giving it some bone meal or using a high phosphate fertilizer for blooming. Phosphorus is the middle number (Example: 10-20-10). Anything that produces a flower or a fruit consumes more phosphorus, so this should help.
Many insect pests attack gardenia plants. If the plant is outdoors, then it could be snails or, more likely, slugs. Both come out to feed at night so you may not even see them. Aphids, mealybugs and thrips also commonly munch on these plants, sucking the life right out of them. Spraying the plant with neem oil can help with these and most other pests. It is organic, being safe for other plants, and is harmless to pets and people.
Gardenias require frequent fertilizing to ensure healthy plant growth. Fertilize monthly between April and November. A balanced fertilizer or compost will work, but keep in mind that these plants do best with acidic soil. Therefore, you’ll want something that is aimed at and specifically formulated for acid-loving plants. Miracle Gro is fine per directions on the package, or you can use a slow release fertilizer like Osmocote. Be careful not to over fertilize gardenia plants. Too much fertilizer can lead to salt accumulation, which can damage the shrub. Do not fertilize gardenias in the fall, which can stimulate growth. This tender, new growth will quickly die when exposed to cold winter temperatures.
This sounds like sooty mold fungus, a foliage disease that turns the leaves of the gardenia black. It doesn’t injure the plant, but it does prevent sunlight from getting to the plant via the leaves, so the plant doesn’t perform as much photosynthesis and can inhibit growth. Sooty mold is normally a good indicator that insects are present, as the fungus thrives on the honeydew created by gardenia pests like aphids. If you control these pests, you will also be able to control the disease. We recommend treating the plant with neem oil, which takes care of both the insects and the fungus.
Gardenias are really sensitive to changes in temperature and do not like being too cool. That being said, they can normally handle temps around 60 to 65 degrees F. (15-18 C.) at night with warmer temps during the day. Planting the gardenia in a place that will protect it from cold days (e.g. walls retain heat, which will help warm the plant) will ensure its survival. Mulching and wrapping the plant in the winter or high winds will also help protect against the cold. If cold weather and winds are particular issues where you’re located, then potting the plant up and moving it indoors would be a good idea. It could spend nice days outdoors and simply move inside if poor weather is expected. You can cut the brown, cold damaged areas off the plant.
Gardenias love a moist environment, but they don’t like being drenched and having water on their leaves. If your gardenias have brown leaves, this can be due to poor drainage, not enough humidity or pests as well.
Issues with gardenia buds falling off plant is a common problem that many gardeners experience when growing this plant. This can be caused by a variety of things. Probably the most common reason is a change in location. Gardenias do not like to be disturbed, so if it’s been relocated lately, this could be why. Dropping of buds can also be due to improper watering. Gardenias like to be kept moist. If they are allowed to dry out too much, or if they don’t have enough humidity, they will respond by dropping their buds. Additionally, the problem could be thrips. We have found neem oil to be effective against pests like this.
We all have questions now and then, whether long-time gardeners or those just starting out. So if you have a gardening question, get a gardening answer. We’re always here to help.