Hidden Valley Hibiscus
Growers & Hybridizers of Exotic, Tropical Hibiscus
How Much Sun do Hibiscus Need?
Hibiscus Newly Planted in Full Sun
Foliage is Less Lush, and Plants Need Daily Water
But Lots of Blooms!
Although they often thrive in completely sunny locations, hibiscus do not actually need as much direct sunlight as is commonly thought. Our own experiments have shown that 2 hours per day of direct sunlight is enough to stimulate blooming, even indoors through a window! However, if the hibiscus receive insufficient sunlight you will end up with pretty green bushes without blooms.
Hibiscus do best with the proper balance of sun, heat, and water. Sunlight and temperature are 2 factors that work in opposition to each other. In other words, if the temperatures are high sunlight should be reduced. If sunlight is high, lower temperatures are better. When both sunlight and temperatures are high water needs go way up and when either or both sunlight and temperature go down so do the water needs of the hibiscus.
OK, so what does this mean in practical terms? Let's consider some common examples:
Along coastal California where the temperatures are often quite mild, it is best to provide a location with lots of sun. We have seen even the most fancy of modern varieties of hibiscus thrive in all day full sun and in fact grow them that way in our own yard.
In the hot and dry conditions of inland California or southern states like Arizona it is best to grow hibiscus in a location that has a lot of shade but some direct sun.
In states that are hot and humid like Florida or coastal Texas, a location that is partly shaded is often best, although frequent clouds and rain reduce the need for shade and hibiscus can be successfully grown in full all day sun.
If your preferred area is on a porch with only morning or afternoon exposure to direct sunlight, that is just fine. A growing location near trees that allow filtered sun plus some direct sun is also good for hibiscus.
Sunburn on Hibiscus Leaves
Hibiscus can sunburn! This only happens when they have been grown in a lot of shade, in a house, or in a greenhouse, and then are moved to a location with a lot of strong, direct sun. The strong sunlight destroys part of the chlorophyl in the leaves, and the result is that part of effected leaves turn a bright white color. This is rarely a longterm problem. New leaves will grow in that are accustomed to the strong direct sunlight and that will not burn. To avoid this situation try introducing your new hibiscus to direct sunlight for just an hour the first day, and then increasing the exposure gradually over a week or two. Hibiscus quickly adapt to the amount of light they receive, but moving them quickly from shade to direct sun may result in the white sunburn effect on some of the leaves.
You may find that your hibiscus bloom just fine in one shaded location but not in another. This is often due to the amount of usable light that the hibiscus receive during the day. It is the total amount of PAR (a measure of the light that causes photosynthesis in plants) that determines whether there is enough sunlight for hibiscus to grow and bloom well. With full direct sunlight for much of the day there is always enough PAR. In locations that are shaded some or much of the day the amount of indirect sunlight contributes to the total PAR the plants receive each day. The brighter the shade, the more PAR there is. This means that the type of shade matters as well as the length of time hibiscus spend in the shade. Dappled light near trees is likely to contain more PAR than shade created by a fence or house that totally blocks direct sun. Choose your growing location with this in mind - the PAR of the direct sunlight plus the PAR of the indirect sunlight (in the shade) equals the amount of usable light that a plant receives in any location. If the PAR is too low for hibiscus to bloom then the plant needs to be moved to a place that receives either more direct sunlight or a better quality of indirect light.
In mid-summer heat, hibiscus will still produce lots of buds, but sometimes these buds will fall off before they open. Rats! The only thing you can do is to make sure the plant is not under any stress from lack of water, and perhaps to move the plant to a cooler, shadier location. Remember what we said - heat, sun and water need to be in the proper proportions for best performance by hibiscus. In mid-summer heat will go up, so sun should go down and water should go up. If it is not possible to move the hibiscus to a less sunny location, then it is critical to increase the frequency and amount of water they are given. Even with this treatment there may be times in summer when blooms just do not make it all the way to opening.
Not to worry though! When the temperatures cool as summer wanes, the plants begin to bloom spectacularly once again. This is all part of the normal process, so don't let it concern you overly much.