When it comes to ornamental plants, flowering shrubs are perfect for introducing a sea of color into your garden, while also providing structure with the foliage and branches throughout the year.
Here’s everything you need to know about the thryallis shrub, including where to grow it, how to care for it, how to prune it, and how to make the most of it in your green space.
At a Glance: What You Should Know About Thryallis
Thryallis is a smaller shrub than many, staying fairly compact as a tropical evergreen, but its real beauty comes from its flowers.
It does need a warm climate to survive, so if that doesn’t sound like your garden, you may be better off with other flowering shrubs such as rhododendrons or hydrangeas.
You can overwinter thryallis indoors, if you prefer.
Give a thryallis shrub the right conditions, and it will provide you with gorgeous, bright yellow blooms pretty much year round.
It can reach anywhere from 6 to 9 feet tall, depending on how you prune it, and the conditions you grow it in, usually forming an oval. You can keep it smaller if you wish, at a more manageable height of 3 or 4 feet.
You’ll often see it labeled as gold shower, shower-of-gold, Galphimia glauca, or Galphimia brasiliensis, but the last two are mistakes. The scientific name for this striking plant is Galphimia gracilis, as those are two different plants.
You can tell Galphimia gracilis apart from other members of the Malpighiaceae genus by its flowers.
The thryallis shrub produces huge clusters of yellow flowers (see also How To Grow The Privet Shrub), and many are open at the same time, while Galphimia brasiliensis only opens two or three at once, and Galphimia glauca will keep its flowers even when the fruit has appeared.
It’s also worth noting that the common name which is most typically used, Thryallis, used to be the genus name before it was reclassified under Galphimia. This old name is the one that has stuck for this particular plant.
How to Recognize a Thryallis Shrub
Thryallis shrubs feature striking silvery green foliage, producing bright yellow blooms with crimson eyes pretty much year-round. Younger growth features warm reddish stems.
Each branch remains fairly soft, moving with the wind. The flowers themselves reach about 2cm wide, and while they stay petite, they make up for their small size as they open in huge clusters.
They do have a light fragrance, which is never in danger of being overwhelming, but it is a nice benefit if you plant a thryallis near a patio or seating area.
The flowers attract plenty of pollinators, bringing more wildlife into your garden, and helping to support its ecosystem and overall health.
How to Care for Thryallis
Sunlight and Position
The more sunlight you can give to thryallis, the better it will thrive, and the more flowers it will produce.
Keep it somewhere sheltered, where the wind cannot get to the flowers and knock them off the shrub prematurely.
You can keep it somewhere shadier, if that’s what you have, but there will be fewer flowers on each cluster, and the overall growth may be a little thinner.
Just make sure you do choose a sheltered position, where it is protected by walls, taller shrubs, or something else which will block out the wind.
Thryallis shrubs like well-draining soil which are somewhat sandy if possible.
You can grow them in areas which do get winters, but freezing temperatures do mean that the plant will die back to the ground, emerging again in the first few weeks of spring. The growth will also be more limited.
Thryallis shrubs can withstand long dry spells without water, but this is provided that the plant is mature and robust enough to do so.
Young thryallis plants, or recently repotted or relocated shrubs will need some time to adjust, where you will need to water them more frequently. This will help encourage the roots to establish.
One thing you must avoid is overwatering. Let the soil dry out at least a little before you water it again, as the thryallis shrub is particularly prone to root rot.
Should You Feed a Thryallis Shrub?
You don’t need to feed thryallis shrubs, but you can if you want it to grow slightly faster in a short period of time.
It’s helpful to fertilize thryallis if you’re growing it in poor soil or a container, but don’t overdo it. Keep in mind that you can tip the balance of the nutrients already existing in the soil, and this can lead to problems.
If you must, fertilize it when it is flowering to support its bloom production, using an all-purpose feed, every few weeks or so.
Pests and Disease to Watch Out For
Provided that you keep a thryallis shrub healthy, by keeping it in bright sunlight for at least part of the day, somewhere where it has good air circulation, this plant isn’t usually bothered by pests or disease.
Keeping the plant healthy goes a long way in terms of prevention. Having said that, it may get the occasional attack from spider mites, and you need to get on top of any infestation fast.
To treat a thryallis which is infested with spider mites, use a diluted mix of neem oil and water to treat it.
To prevent fungal disease, keep the shrub somewhere well ventilated, and water it in the morning, so that excess water can evaporate readily.
How to Promote Thryallis Flowers
If you live somewhere colder, you can encourage flowering by cutting back the plant in spring, and then the shrub will treat you to sunshine-yellow flowers from the last few weeks of summer into autumn.
If you live somewhere warmer, the shrub will flower pretty much year-round.
Growing a Thryallis Shrub in Your Own Garden
You can grow a thryallis from seed, or from cuttings, if you don’t want to buy the plant outright. If you start them from seed, you need to do so in early spring, and pot them on as necessary.
If you’d prefer to skip some of the waiting and grow them from cuttings, start cuttings off in summer, and help them along by using rooting hormone powder.
To help bolster your chances of success, take several cuttings at once, planting them in the corners of a small square pot, filled with moist, well-drained soil.
Keep them somewhere bright, humid, and warm, and you should see some new growth appearing within six weeks or so.
It’s worth mentioning that a thryallis can grow up to 4 feet in its first year if the conditions are right, so give it plenty of room where you can.
Thryallis is a great plant to use as a screen, hedge, or border plant (see also Plants For Borders) in a sheltered and sunny position. You can grow it indoors too, but it won’t grow as well as it does outdoors.
Frequently Asked Questions
Is a Thryallis Shrub Invasive?
No. While it is a vigorous plant that puts out a lot of growth, and it’s considered an exotic plant outside its native Mexico, it’s not classed as invasive.
Can You Grow Thryallis in Pots?
Yes. There’s no reason why you can’t grow thryallis in pots if you prefer.
If you live somewhere which gets cold winters, it is much easier to grow thryallis in a pot, so that you can take it indoors during the winter, sparing you the task of either digging it up or wrapping it in horticultural fleece.
Keeping it in a pot won’t prevent it from flowering, though it may grow a little slower.
Will Thryallis Survive in Salty Soil?
To an extent, thryallis will adapt to different conditions. Yes, it should tolerate soil which has salt in it.
How Do You Prune Thryallis?
Make sure your pruning shears or tools are completely sterilized before pruning your thryallis shrub, otherwise you risk introducing disease to the plant.
Use garden shears to cut off any dead or diseased wood back to the base. Carefully dispose of these, and clean the shears. Then you can tackle the rest of the shrub with a hard pruning, which only needs to be done once a year, in either fall or winter.
Cut healthy, new growth back to the first true bud of the plant, and while this might look ugly, it will promote healthy growth for the following year.
If you just want to give it a trim to keep it tidy, do this during spring. Shape it as you see fit, using sweeping cuts, making sure to take a step back to keep from taking too much off at any one time.
After you’ve given it its spring haircut, let the plant grow out again, as the flowers will appear on the ends of the branches.