Growing exotic hibiscus is not an easy task and takes several years to master. There is a learning curve that spans multiple growing seasons.
A Quick Bit of Hibiscus History to Understand What is Needed
So Why Does Where They Come From Matter?
Soil & Feeding
Being that hibiscus originate in tropical climates for many millennia they are genetically programmed for the unique conditions of such regions.
These are volcanic areas where the soil is rocky and extremely porous. Such soils are very rich with minerals and abundant with air. Your soil needs to be the same – we recommend a light potting mix and add ample amounts of perlite and/or pumice stone
Do not add composted materials and very little worm castings as these will lose all air when wet and deplete the soil of the needed air to sustain hibiscus root systems.
Hibiscus roots are tender and need constant air so native soils like clay are a recipe for root rot and a quick demise of your plant. Make sure to dig as large of a hole as possible. We recommend at least 2-3 ft around and about 1 ft deep in ground.
For potted plants make sure you use pots that have many drainage holes and do not layer the bottom of your pots with any type of rocks as they will actually form a seal. Also hibiscus roots can quickly plug up those drainage holes so you will need to root prune. We have a great video on how to do that: https://www.youtube.com/watch?v=u9GCLZFinaE
Volcanic soils are high in minerals so hibiscus are used to high amounts of nutrients all the time that are easy to get. They have unique requirements that differ from other flowering plants. Lots of potassium, very low phosphorus and low nitrogen. We recommend the fertilizer from Hidden Valley Hibiscus which is formulated just for hibiscus http://www.hiddenvalleynaturearts.com/acatalog/fertilizer.htm
Temperatures, Metabolism and Sunlight
Tropical climates do not have seasons so temperatures are normally 60-95F. Hibiscus thrive in these conditions and get stressed when living in extremes on either side of this spectrum
Temps below this range will start to slow your plant’s metabolism. Here in So Cal we have observed when under 50F you will start to see a significant slowdown which show through monotone blooms that are smaller, reduced or no growth and the pads on your blooms might disappear.
Reduce watering proportionately with the drop in temps. Your plant is not up taking as much water and if it rains that will start to remove the air from your soil which is worst case scenario for hibiscus.
Also reduce fertilizer since less water is being absorbed it will build up in the soil and when your plant returns to normal metabolism this will lead to severe fertilizer burn which can even kill a plant.
Hibiscus leaves are not genetically developed to be in direct sunlight over 95F so that will start to stress your plant. You will notice yellow leaves appearing, buds dropping and smaller sized blooms.
Your plant’s metabolism will continue to accelerate as the temps rise which means not only is it up taking more water but also more fertilizers. So it is important to also reduce the amount of fertilizer your plant is getting. We recommend for every 5 degrees you reduce the amount of ferts by 1/4. This is a good rule of thumb for both when it is hot or cold.
If temps exceed 105F we recommend just water only
Southern California Hibiscus Growing by Region
The Southern California Coastal Plain is the most ideal area for hibiscus to grow due to the strong marine air influence of the Pacific Ocean which acts as a moderator for temps.
Coastal areas that see less sunlight and cooler temperatures should have hibiscus growing in maximum sunlight year round. Hibiscus thrive on heat to grow and create colorful blooms so shady areas are not going to work well for them near the coast.
Inland Valleys are a challenge during the winter and summer as the temperature extremes can be significant. Also these areas are prone to Santa Ana wind events which are enemy #1 for hibiscus – cold and dry is the exact opposite of what they need. Winter hibiscus need full sun especially in the morning after a cold night. Summer they need dappled shade to protect them from direct sunlight over 95F
Inland Empire and Desert areas are a challenging region to grow hibiscus. They cannot tolerate freezing temperatures plus the strong Santa Ana wind events during winter. The summer extreme heat is also too much for them to tolerate in direct sun. Most growers in these areas grow their plants in pots and move them indoors during winter and under shade in summer.