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Gardenia plants are garden shrubs that look and smell gorgeous in the spring and summer. Come the fall when night temperatures cool, and they begin to lose their color.
By winter, when temperatures drop below around 15oF the leaves turn brown, or if it gets a severe touch of frost, you can wind up with black leaves. That’s not the pretty foliage you’d be expecting.
If you’re in a region that gets cold winters, you’ll need to know about Gardenia care in the winter, especially, if you’re growing the varieties of Gardenia that get so big that it’s impossible to remove them from the ground to overwinter them indoors.
The Types of Gardenias that Can Survive Light Frosts in the Winter
The Gardenia plant has over 200 species. Very few are frost resistant. The majority are tropical plants that are likely going to need to be overwintered indoors.
The most frost resistant variety is (no surprise) the Frost Proof Gardenia. It’s not immune to frost though. A light touch of frost won’t do much damage but sustained temperatures below zero Fahrenheit won’t bode well.
The Frost Proof Gardenia can reach heights of up to 5 feet making this the type of gardenia variety to grow in USDA zones 6B or 7, right on the fringe of where any other Gardenia variety can survive – Zones 8 through to 11.
As a guideline, typical Gardenia plants need consistent temperatures of 15oF. If you’re in an area that gets sustained winter temperatures below that, stick with low growing Gardenia varieties. The type that only grow to one to two feet in height, making them ideal to keep in pots or containers indoors in the winter and move them to the garden when springtime temperatures arrive.
The temperature to keep in mind are 15oF to keep them alive and 60oF is needed for Gardenia plants to bloom.
Knowing those temperatures, you can make a plan to care for your Gardenia this winter, preventing frost damage from occurring.
Protecting Outdoor Gardenia Shrubs from Cold Wind Damage
That’s caused by water inside the plant stems freezing up, preventing it from reaching the leaves. The leaf discoloration is essentially caused by drought because water can’t travel through the plant when it’s frozen.
To protect your outdoor Gardenias that are too large to bring indoors, or if you’re only expecting a brief cold spell, you can shelter and insulate them with a blanket. Burlap or fiber blankets can do the trick.
Fabric coverings for plants prevents freezing cold air from coming into direct contact with the leaves. Almost any fabric can be used so long as it’s porous enough to allow moisture to escape.
You don’t want to just throw these over your plant though. That can crush stems and break branches. Blankets need support and should be added with stakes.
Cut stakes of wood in sizes slightly lower than the height of your Gardenia. The goal is to make a perimeter around your shrub so you can toss a blanket over it.
If you stake it higher, it’ll introduce a weak point for cold air to linger around. The closer you can have the blanket “resting” on top of the plant, the warmer the air inside will be.
If it’s going to be windy, a staple gun’s handy to securely attach a blanket to the stakes.
To up the ante and increase ambient temperatures under the blanket, add some water. The soil will naturally increase the temperature slightly, as will the plant through transpiration.
As water evaporates, it increases the air temperature. A good way to protect against frost is to use gallon buckets, jugs, or bottles of water that are placed under the canopy to help moderate air temperature around the plant.
How to Overwinter Gardenia Plants Indoors
Many a Gardenia variety can be grown in containers, whether placed on the patio, or planted in the garden inside containers.
Typically, these are the types that grow from 1 to 2 feet in height in the dwarf Gardenia varieties, or those that reach 3 to 4 feet tall (such as the Veitchii) that can have their growth contained by pruning.
Indoors, in the winter, there are a few things you need to take control of to overwinter a Gardenia successfully:
- The temperature swings between day and night
- Humidity levels
- Light intensity
Gardenias prefer day and night temperatures to be similar. They start to struggle when night temperatures get cooler by more than 10oF.
The preferred temperatures are 65oF daytime, and 55oF nighttime temperature.
Controlling the humidity levels around Gardenia plants indoors may require a little help from a small humidifier. Naturally, with indoor heating systems, the air is drier.
Gardenias prefer humidity levels to be consistently above 60%. Most homes don’t have the room humidity above 50%. Above that is generally uncomfortable for you, which is where a mini humidifier comes in.
Not a room humidifier, but a mini-sized one that can sit near your container, giving it a spray of cool mist periodically. Think of it more like a device to automate the misting of the plant to increase humidity.
In the winter months, daylight hours are shorter and the sunlight not so bright. Gardenias favor full morning sun but can cope in shaded conditions.
When the sunlight intensity isn’t as bright, there’s two ways to get the brightness levels up to what it needs.
The first is the simplest and that’s to place your potted plant near a south-facing window. In any other season, indoor Gardenias would be placed near an east-facing window to catch the full morning sun while benefiting from afternoon shade.
In the winter when temperatures are cooler, they don’t need shade from afternoon sunlight.
The alternative is to give them four to six hours of artificial light using full spectrum grow lights. The purpose of these is to replicate the outdoor conditions indoors.
Controlling Moisture is the Troublesome Part for Gardenias Indoors
Having less sunlight, Gardenias typically planted outside then brought indoors for the winter won’t drink as much. The concern that raises is overwatering.
Ideally, the soil should be kept damp but not to the extent that it’s soggy. If these are left in standing water, they are susceptible to root rot, not to mention the plethora of soil-borne diseases caused by soggy soil.
A safer watering practice for indoor Gardenias is to let them dry out to the point of wilt, which is the plant’s way to show that it’s dehydrated.
It’s not the healthiest method because it will stress the plant. It won’t kill it though. Overwatering it will. When your only concern is keeping the plant alive until the spring to get it back into the garden, a little stress isn’t the end of the world.
This applies to most plants indoors (at least the stress tolerant ones anyway) because it’s easier to recover a plant from drought than it is to heal a plant of root rot, which usually kills plants if it’s not caught early enough.
Arm Yourself with Insecticidal Soap to Keep the Insects at Bay
Whenever you have indoor plants being kept at high temperatures with high humidity and bright light, it’s an attraction to pest insects. In particular, whiteflies, and spider mites.
Both of those can be protected against with regular applications of neem oil or a similar horticultural oil.
Prepare to do battle with these before you bring your Gardenia indoors because they are likely to become a nuisance.
Read… 10 Foolproof Ways to Get Rid of Bugs on Indoor Plants for a list of ways to control insects on any indoor plant!