Hibiscus Plant Care
My Hibiscus Leaves are Turning Yellow!
Yellow Leaves on an Otherwise-Healthy Plant
The First Sign of Spider Mites
Spider mites pop up in hot, dry growing conditions, such as a very sunny window inside a house or outside in high heat in a dry climate. Spider mites don't tolerate rain or plants that get wet frequently. They need dry plants in high heat to survive. If you are seeing yellow leaves on your plant and it is raining every day, this is not spider mites! Spider mites die in that kind of rain. Rain alone can cause leaves to turn yellow if it goes on and on. But if you are seeing an increasing number of yellow leaves and your plant is inside a house in a sunny window, or outside in a hot dry summer, then chances are that your hibiscus does have spider mites. In these kind of perfect, hot, dry conditions, spider mites can reproduce rapidly and eventually kill off every leaf on your plant, so it is important to deal with them as early as possible.
Yellow Stippled Leaves that Don't Stop
Leaf Stippled by Spider Mites
Spider mites cause this tell-tale "stippled" look on leaves. A leaf or two first gets a mottled dirty-ish yellow mixed into its normal green color. Leaves become stippled as the mites pierce the leaves and draw out chlorophyl from them, leaving colorless leaf spots behind. Then slowly the entire leaf turns yellow, dies and falls off the plant. At first you just see a few yellow leaves, here and there, and don't think anything of them. But as the spider mites reproduce on your plant, you see more and more yellow leaves, an increasing number over 2-3 weeks, and your plant is slowly losing its leaves. When this happens, it's time to inspect your plant for spider mites!
Tiny Crabs on Tiny Webs
Spider Mite under Magnification
An Advanced Case of Spider Mites
Look Closely to See the Webs & Mites on Growing Tips
Leaves Show the Typical "Mottling" of Green & Yellow
Plant Defoliated by Spider Mites
How Do I Get Rid of Spider Mites?
Over the years, we've written many articles on how to control spider mites. The methods below are the ones we have found to be most effective at killing spider mites with the least amount of harm to the hibiscus plants. The method each of us chooses depends on the circumstances - how many hibiscus plants we have, how big the plants are, whether they are indoors or outdoors, in a house or greenhouse, in pots or in the ground, etc. At HVH we have hibiscus growing in the greenhouse, in the ground in an outside garden, indoors in a house environment, and outside on porches and decks in pots. We use different pest control methods for each of these different sets of hibiscus. Very few of us have extra time to waste, so efficiency matters! Both of these methods work. It's just a matter of finding the method that's quickest, easiest, and most efficient for your hibiscus and their growing circumstances.
DROWNING SPIDER MITES
This is our favorite method for all hibiscus growing in small-medium pots and for houseplant hibiscus. You only have to do it ONCE to kill all spider mites and their eggs. It kills every kind of spider mite, even the most microscopic ones that can hide in cracks in the bark. This method does require precision and care. You'll need a timer and a thermometer - a kitchen "candy" thermometer is perfect. If the water is too hot or you leave the plants too long, you can damage the leaves and they will all fall off after treatment. If the water is much too hot and you leave the plants much too long, you could actually kill a very young plant. But if the water is too cool or if you don't leave the plants in the water long enough, you won't dissolve the covers of the eggs and kill the growing larvae, which means the infestation will come right back.
A Large Sock on a Small Pot
- Wrap the hibiscus plant pots in some kind of fabric or extra heavy aluminum foil and use a twist tie to secure the fabric or foil around the base of the plant. Fabric and aluminum foil let water through to the pot, while keeping the soil in place, so any spider mites in the pot will be drowned. Don't use plastic bags to secure your pots or you will carefully protect any spider mites that are living inside the pot and soil. Large socks or pantyhose work well, as does cheesecloth to wrap up small pots, and pillow cases work well for large pots. Extra heavy aluminum foil works for pots of any size.
- Lay several hibiscus plants on their sides, pots and all, in a bathtub. You can put many of them close together in a single layer in the bottom of the tub.
- Fill the tub with water that is bathwater temperature - about 90°F (32°C). It should not be so hot that you can't comfortably keep your skin in it. What feels too hot to skin will risk damaging your plants' leaves.
- Fill the tub until all the plants are covered, and weight the plants down to make sure all parts of all plants are submerged in the water. (An easy way to weight them is to cover the plants with two large towels, then to pull the two shelf racks out of your oven and lay those carefully over the top of the towels.)
- Leave the plants submerged in the water for 45-60 minutes.
- Drain out the water and stand the plants up in the tub until the excess water drains out of the pots.
- Remove the fabric covers, and scoop any loose soil in the fabric back into the plant pots.
- Leave the plants out of bright light for a few hours to rest, then put them back where they belong. Be careful not to water the plants again until the soil dries out after this thorough soaking.
Unless plants are recontaminated by exposure to another infected plant, plants should remain free of spider mites, aphids, and other pests for 4-6 months or more. This method has the added advantage of leaching out any build-up of fertilizer salts in potted plants, which needs to be done once or twice a year. So it is two plant-care activities in one.
WASHING OFF SPIDER MITES
This method works for large hibiscus in pots or for hibiscus planted in the ground. It is time-consuming though, because each plant must be washed slowly and carefully. However, it can be fun to go outside and get wet with your hibiscus on hot summer days, and many people find that they enjoy it!
- If plants are in pots, lay them on their sides where the pots can be rolled over to all sides. If plants are in the ground, get a long enough hose that you can walk all around each plant.
- Using a hard stream of water, wash every single millimeter of each plant - the top and bottom of every single leaf, branch, stem, and twig. Spray systematically, making sure you don't miss one spot on the plant where spider mites could be lurking. Spider mites live mostly on the bottoms of leaves, so spraying the bottom of each leaf carefully is crucial. A BugBlaster makes this job much easier because it sprays out in all directions, up, down, and sideways to both sides. It's very hard to do this with a garden hose.
- When finished, wash the ground with a very strong stream of water and enough water to drown any spider mites that fell off the plants.
- Repeat this washing process 4-5 more times every 5-7 days.
FINISHING TREATMENT WITH HORTICULTURAL OIL
To increase the effectiveness of either of the above water methods, you can follow up either water method with a treatment using Horticultural Oil. Water drowns the spider mites, but if any survive, hort oil will smother them to death.
Although hort oil is a non-toxic, organic product, it is still very bad for human lungs! It clogs up our lungs the same way it clogs up spider mites' breathing tubes. If you ever inadvertently breathe in even a little bit of hort oil, you will feel how painful it is to your lungs. So ALWAYS wear a mask of some type. Even just a paper painter's mask that covers your mouth and nose will protect you, since the particles of hort oil in the air are large and gloppy and will stick to the mask instead of passing through it. If you forget to get masks at the store, at the very least, tie a heavy bandana (or even a T-shirt!) around your face! Hort oil is one of the easier products to block, but it is also extremely important that you do block it from entering your lungs!
Like every kind of plant pest spraying, it's best to spray in the evening when the plant can be protected from the sun for the hours that the hort oil is doing its work. Hort oil is stressful for plants too and also blocks their transpiration (breathing), so you want to make this stress as gentle as possible for your hibiscus. If you spray during the day, the sun can burn and damage the leaves that aren't doing their normal transpiration, so it's important to protect your plants from the sun and give them 8-12 hours to recover from the effects of the hort oil in cool night-time darkness.
Here is how you use Horticultural Oil as a finishing treatment for spider mites:
- During the early evening hours, put your potted hibiscus in a protected place outside with enough space to walk all around each plant.
- Follow the directions on the bottle of horticultural oil to mix it with the proper amount of water for whichever product you have.
- Put on a respirator mask, painter's mask, or heavy bandana covering your mouth and nose.
- Carefully and systematically spray every millimeter of your plants: tops and bottoms of every single leaf, stem, branch, and twig, as well as the surface of the pot and soil. It takes time to spray this carefully, but you may as well not bother spraying at all if you don't do it this carefully! Spider mites live mostly on the bottoms of leaves, so spraying the bottom of each leaf carefully is crucial.
- Let the spray product dry for overnight before bringing the plants back into a house.
PREVENTING FUTURE SPIDER MITE ATTACKS
Preventing spider mites is a matter of two basic rules that, if followed, will save you hours and hours of hard work and misery for your plants:
- Isolate all new plants that you bring into your hibiscus collection. NEVER put a new plant with your existing plants. Keep all new plants in isolation for several months, and isolate them from each other, so they aren't touching each other. Most spider mite infestations start from a new plant that comes from a new nursery.
- Wash your plants once a month. Some spider mites will blow in on the wind from outside weeds and plants, or through a central heat or air conditioning system in your house if you have ever had a spider mite infestation. Prevent these stray spider mites from getting a foothold on your plants by thoroughly showering your hibiscus once a month. Invest in a BugBlaster, put on your swimsuit, and spray every side of every leaf, stem and stalk of all your plants monthly. It can be a big job, but it's also fun in the hot summer weather, and it has the added advantage of providing extra hydration for your plants and extra cooling during summer heat. If you live in a dry climate and want to wash them weekly, that's even better! If you wash weekly, you won't have to be quite as careful about how well you do it. Just get up under and over branches all around the plants, and let the BugBlaster do the work.
The trick with pest control is conscientiousness. All these methods will work if applied conscientiously following the directions exactly. So find the method that's easiest and most comfortable for you to follow!