Growing Hibiscus in Pots...by Father Robert Gerlich
Why Grow Hibiscus in Pots?
Many members of the Mallow family tolerate cold very well. In fact, Altheas, Rose Mallows and many others thrive as far north as St. Louis. Some species will even prosper in frigid Canada. But this is NOT TRUE of Hibiscus Rosa-Sinensis. Faithful to its tropical heritage, it will not tolerate many hours of below freezing weather.
If temperatures are expected to drop below 32°F for more than a few hours, hibiscus need protection. In our area we have years without a serious cold snap. Even the light snow of Christmas day 2004 and the brief snow flurry in Spring 2009 did no real damage to unprotected plants. But there are years when cold weather sends us scurrying to cover our favorite plants again and again.
Because winters in the New Orleans area are so “iffy,” pot culture is an attractive alternative to planting hibiscus in the ground. Potted hibiscus can be sheltered into a greenhouse, garage, or covered porch, while plants in the ground are harder to cover and protect.
Pot culture also allows us to move plants easily for both decoration and cultural requirements. Potted hibiscus can be "pampered" by moving them to areas with better sunlight or more protection from hot afternoon sun. And plants in bloom can be used to grace patios or pool areas.
Potted hibiscus offer another advantage -- earlier blooms. Hibiscus bloom better if grown in a somewhat root bound condition. If a plant that can grow to 20 or 30 feet tall or more is planted in the ground, the first thing that it does is “reach for the sky.” While they are growing quickly and large like this, plants rarely bloom much until mid-to late summer and fall each year, when they reach a size closer to their potential. For these reasons, many hibiscus "fanatics" keep their hibiscus in containers.
On the other hand, container culture can be a bit tricky, since radical and potentially lethal fluctuations in temperature, pH, and moisture occur more readily in container culture. In short, hibiscus in containers demand more attention and closer monitoring. if you don't wish to invest the time and/or lack the plant savvy necessary to care for a potted hibiscus, plant them outside in a sunny, but protected spot and take your chances with our winters. They are actually pretty good.
Choosing the Right Cultivar
While any hibiscus will grow in pots, some cultivars are rapid growers quickly outgrowing the container; some are more sensitive to overwatering; some are more less able to tolerate pH fluctuations. In short, some cultivars offer a better change for successful. When selecting a plant for container culture, ask a nurseryman or hibiscus grower for a plant that does not grow too large, too quickly and that has a proven tract record in pot culture.
Of course, sometimes information about a particular cultivar is not available. In that case, be sure to watch for the particular characteristics of the cultivar and adapt the growing technique accordingly. Should a plant fail, reexamine the growing techniques. If they have been sound consider trying again (sometimes it is very difficult to determine why a plant “up and dies”) or try another cultivar.
Choosing a Container
If purchased from a nursery, potted hibiscus are probably growing in a one or two gallon black nursery pot. Tilt the plant our the contained and take a good look at the roots. If the roots are wrapping around each other, it is time to repot.
Move the plant up one, or at most two sizes, up from the container size it is presently in. From a gallon or two gallon size pot, move the plant up to a 3 gallon or 10-12 inch container. But size is only one of the issues in selecting a pot.
Pots made of clay are good for stability, and they are less likely to overheat or retain too much water, as sometimes happens with plastic pots. But these pots are more expensive, break easier and generally have only one hole in the bottom. Most growers use some type of "colored" plastic pot. Beware of black plastic in the sun--they heat up dramatically, even to the point of injuring the roots.
Unless you are a very astute waterer, any pot you choose could benefit by having more drainage holes. If there is someone around who can drill more holes in the pot, then go ahead and do so. If not, choose a pot that has at least 4 holes already in it.
Another option is to use a plastic pot, but to place it inside a larger and heavier clay pot. This will help to keep the plastic pot from "overheating" in the hot summer sun. You may wish to fill the space between the two pots with stones. This will help stabilize the plant during windy weather.
Another strategy is to bury the clay pot in the ground and then place the plastic pot inside it. Mulch over well. In the winter, the plants can be easily removed for winter protection.
Potting Soil - The Key to Success
Choosing the right potting soil can make all the difference in the success you will have with the potted hibiscus. Drainage is the key!
When a plant dies, its decline normally begins in the roots. For that reason, one could say that the "heart" of a plant is its roots. Insects and disease, if severe enough can kill any plant, but normally a healthy plant can shrug off these attacks. But no plant survives a critically damaged root system. Protecting and nurturing the root system is a grower's first order of business, and the selection of an optimum potting mixture is of central importance.
Be sure to use a mix that is made specifically for pots--not mulch or compost or other products made for using in garden beds. Good drainage is key so be sure that your mix is porous. Hibiscus like to have water run over their roots, but they do not like being overly wet. When the plant is over-watered, the soil compacts and presses the oxygen out of the root zone. If this happens the roots literally suffocate.
Unfortunately, most commercially available potting mixes are “too heavy” for hibiscus. Several brands of “professional” potting mixtures made especially for containers are widely available. Even so, it is a good idea to amend these products with sharp clean sand, perlite, or composted bark.
A standard and popular mix among growers is a combination of 5% perlite, 50% peat and 45% composted hardwood bark. In recent years, however, coco coir has been used increasingly to replace some or all of the peat. This processed coco fiber is less likely to pack and lasts twice as long as peat before it breaks down. Its principal drawback is that it is still hard to find at local nurseries.
Gently ease the pot off the root ball. If the roots are circling the bottom of the pot and form a solid mass at the bottom, it is time for a larger pot. If the plant is seriously root bound, you can cutoff up to a third of the root mass from the bottom and sides and then replace the plant in the same pot with new soil or move it into a larger container.
Now, with pot and well draining potting mix ready, it is time to repot. This is a simple operation and can be done in just a few minutes. Merely place some of the new mix in the bottom of the new pot. Disturb the root ball to allow the roots to spread more easily. The top of the root ball should be about 1 inch below the rim of the new pot. After settling the root ball on top of the new soil, fill in around the sides of the root ball with potting mixture.
IMPORTANT: Press the soil down firmly, DO NOT jam the mix down into the pot. Remember, air is as important as water to the roots and tightly packing the soil mix will force most of the air out of the pot. Just fill in and lightly press on the soil so that the root ball is securely nestled in the new pot.
Placement of Potted Hibiscus
Most cultivars of tropical hibiscus enjoy the sun, as long as they have sufficient moisture. Some few, especially those with brownish flowers appreciate more shade than other cultivars. Six hours of direct sunlight is the general norm. If possible, place your pots where they receive morning or late afternoon sun, but have shade between 12 and 4 pm.
Be sure to give the plants sufficient water in the heat. Remember, water but do not waterlog the plants. Water well (until water flows from the drainage holes), but let the potting medium dry out before watering again.
During the cooler months, water ONLY when the plant is dry. Water early in the day rather than at night, since this gives the plants time to dry out a bit before temperatures cool at night (cool temps and low oxygen levels promote fungal diseases).
Fertilize light but often with a water soluble hibiscus fertilizer. Do not use "blossom bloom" formulas on a regular basis, as they contain too much phosphorus for hibiscus. Tropical hibiscus fertilizers have numbers like 9-3-13, 10-4-12, and 12-4-18.
Every six weeks or so, use clean, unfertilized water to irrigate your plants. This helps wash salts from the soil, preventing unhealthy and potentially lethal levels of salt buildup.