Bluestar Flowers: How to Plant, Grow, and Care For Amsonia Tabernaemontana
Amsonia Tabernaemontana, also known as Bluestars can be a beautiful flowering plant addition to just about any garden. They do contain a milky sap that can be toxic and irritating to humans, but otherwise get along well with many other plants within your garden. In this article, gardening expert Madison Moulton explains how to plant, grow, and care for Bluestar flowers.
Gardens are a peaceful sanctuary for most, offering a litany of calming colors, shapes, and textures. Nothing is quite as calming as Amsonia plants, with their quaint, soft blue star-shaped flowers. Aptly called Bluestars, these dainty blooms sit atop long stems in fluffy clusters, adding a peaceful airiness to your landscape.
When these flowers pop up in late spring, your garden will be treated with the truest of calming blues. Spring isn’t the only time this stunning plant shows off though, adding interest to your garden throughout the year.
Amsonia’s graceful foliage is bright green throughout the blooming season, offsetting its lovely blue flowers. As the months grow colder, the foliage fades into a brilliant golden yellow, ensuring your garden sanctuary stays in tune with the fall mood.
On top of all these benefits, Bluestars are an incredibly easy plant to care for. This of course only adds to its peaceful nature and makes it an ideal plant for all types of gardeners. They look most at home in cottage-style gardens but will work in most garden settings, adding its dust of peace no matter where it’s planted.
Bluestar Plant Overview
Plant Type Perennial
Native Area North America
Hardiness Zone USDA 3-9
Exposure Full to Partial Sun
Maturity Date 2-3 Years
Plant Spacing 12 inches
Planting Depth 6-8 inches
Height Up to 3 feet
Watering Requirements Moderate
Pests and Diseases Rust
Soil Type Well-draining
Attracts Bees, Butterflies
Plant With Hostas
Don’t Plant With Full Shade Plants
History and Cultivation
Amsonia plants are named after renowned English physician Dr. John Amson. He settled in Virginia during the mid-1700s and later befriended the distinguished British botanist John Clayton. Clayton was most famous for his works on New World flora and for naming this genus after his friend.
The genus is made up of a variety of species, with many only being discovered in the 20th century. Some varieties have even been discovered in eastern Asia and the Mediterranean. Amsonia tabernaemontana is the most common in North America, growing natively along the edges of wetlands and across forest floors.
One of the most recent discoveries is the A. hubrichtii, which was first discovered in 1942 and named after its finder, Leslie Hurbicht.
No matter the variety and the slight differences each holds, Amsonias make a great accent plant and are favorites for cottage-style gardens. Their soft blue flowers make spring feel even fresher, while its changing foliage keeps up with the ever-changing seasons.
Amsonias are non-invasive and attract a wonderful amount of butterflies and other pollinators. You’ll often see their soft blue flowers peeking through in butterfly gardens. They’re also relatively deer and drought resistant. As an added bonus, Amsonias are low on the pest and disease-attracting list.
The only downside with this plant is that its milky sap can be mildly toxic and irritating to humans and house pets. As long as you keep them away from prying fingers and paws, you’ll get to enjoy their beauty year-round without trouble.
Propagating can be done in a few ways, either by sowing seeds or taking cuttings. You can also propagate by division, but it’s the most impractical and difficult method when it comes to Bluestars.
Propagating by cutting yields the best results and helps retain chosen species characteristics. Sowing seeds is second best, but results may vary, giving you a stunning Bluestar that has little similarity to the parent plant. Over and above that, propagating by seed can be a slow process.
Propagation From Cuttings
Stem cuttings are by far the easiest method to go for. It’s fast and simple, but unfortunately time-sensitive. Amsonia is propagated by softwood cutting, a method used for a variety of plants, including bluebells and asters.
The best time for cutting is during the softwood stage of your Amsonias growth. This is identifiable by new shoots that are bright green, with no buds or flowers. The stems should snap when bent.
When your Amsonia is at this desirable softwood stage, use a clean, sharp knife to gently cut just below a leaf node. Next, remove any lower growing leaves from the bottom half of the cutting. To improve your chances of rooting, dip the bottom end of the cutting into rooting hormone powder. This stimulates growth and protects the vulnerable cutting from disease.
Now, you can simply pop your little stem in a pot with a damp organic propagating mix. A well-draining material like coconut coir and sand works well, but perlite and vermiculite are also options. The stem needs to be planted about 2-inches deep near the inner wall of the pot.
Stick your pot in a spot where temperatures are maintained at about 60-80F and it can get indirect sunlight. Keep the soil in your pot moist, not soggy.
Your Amsonia cuttings should be ready to be transplanted in your garden in as little as two months. Keep a lookout for new growth and check for signs of rooting by gently pulling on the cutting. Any resistance indicates roots have begun to grow.
Propagation From Seeds
Like many perennials, Amsonia seeds require a cold treatment, or stratification before they can germinate. This simulates the natural process that many seeds go through during winter before they germinate.
Wild Amsonia seeds overwinter in the cool ground with a healthy covering of snow, where they can comfortably enjoy a cool period. Only once the temperatures steadily climb to about 30-40F, do the Amsonia seeds germinate.
Replicating this process is relatively easy. Start by gathering the seeds from dry pods. Fill a tray or container with a seed starting mix that’s well-draining and water thoroughly. Make sure the soil isn’t soggy, but nice and moist.
Next, plant the Amsonia seeds just below the surface of the soil by gently pressing them in. Place a covering over your seeds to create a mini-greenhouse and pop it in a cool room, like a basement. This room needs to maintain daytime temperatures of about 55-60F.
After about three weeks, move your mini greenhouse to your fridge (NOT the freezer) to replicate the icy winter cold. Water as needed, keeping the soil moist. Your Amsonia seeds should be ready to move after about a month and a half.
Once you’ve taken it out of the refrigerator, pop your Amsonia back in that cool room until it’s ready for the great outdoors.
Amsonia seeds can take as long as 10 weeks to sprout and can take even longer, sometimes double that, to be ready for transplantation.
Propagation From Division
Dividing Bluestars may seem easier after reading about the time required for propagating seeds. However, this method requires heavy-duty tools to cut through the thick woody stems and root systems of mature Amsonia plants.
Amsonias also have taproot systems, which allows the system to spread deep and wides, making them very difficult to remove from the soil. Once they are removed, plants with deep taproots typically don’t respond well to division and may struggle to retain their previous growth.
However, older plants that aren’t looking their best may benefit from division if done carefully. This will encourage new healthy growth, after a potential recovery from transplant shock.
To start, loosen the soil around the plant and dig up your Amsonia’s root ball using a clean sharp shovel. Gently remove as much dirt as you can. Next, you’ll need a sharp knife or saw to cut into the thick root ball.
When dividing your Amsonias, make sure to include a section of the root ball, crown, and stem of the plant in each division.
These ‘new’ Bluestars can be replanted immediately in a new garden bed or pot. The longer you wait to transplant, the more likely it is that the plants will encounter transplant shock and struggle to establish. Prepare the new planting holes immediately after dividing and water thoroughly once planted to prevent any permanent damage.
The best time to plant Amsonia is in mid-spring or early fall. Amsonias are readily available for purchase from your favorite garden nursery or local garden center. You can also transplant propagated Amsonias with ease once they’ve matured enough.
Make sure your planting holes are between six and eight inches deep with a healthy 12-inch spacing. Once planted, water thoroughly and frequently until your Bluestar has taken root.
Amsonias make wonderful garden plants, but they’re just as breathtaking in containers on patios, balconies, and even indoors. Bluestars need a relatively large pot; the bigger the better. The pot should be deep enough to accommodate the root system.
Ensure that it has sufficient drainage as Amsonias hate soggy soil. Fill your chosen pot with moist, well-draining soil, pop your Amsonia in, and water thoroughly. As these plants are quite large and tend to take up all the space inside a pot, they are best planted alone.
How to Grow
There are many steps you’ll need to take if you are going to successfully grow bluestars in your garden. You need to have the right combination of light, water, soil, fertilizer, and the perfect climate. Let’s take a look at what you’ll need to have in order to get your perfect flowering harvest.
Even though Amsonias can be found on woodland floors, they flourish in full sun. In full sun spots, Bluestars will sprout more soft blue flowers. They’ll look great along sunny paths or even alongside your open garden pond, for those varieties prefer moist soil.
Bluestars will happily grow in shaded areas that receive dappled sunlight too, like underneath trees or window sills. Amsonias grown in hotter drier climates will be a little more grateful for a shadier spot in the garden.
Too much shade can be detrimental, causing the plant to become floppy and sprawled. Never plant in deep shade, and choose a partial sunlight spot with more sun throughout the day than shade to ensure you get plenty of flowers.
Bluestars require a healthy amount of water throughout their life. In cooler climates, they can be somewhat drought tolerant, happily skipping a day or three of no water. In hot climates, however, your Amsonia’s soil should never go through prolonged periods of dryness as this will result in heat stress.
Specific watering needs will depend on the chosen variety. Some are more drought-tolerant, while others prefer consistently moist soil. Ensure you understand the needs of your Amsonia and provide the right conditions for optimal growth.
Healthy watering practices ensure the health of not only your Amosnias but the rest of your garden too. Always water your plants in the morning to limit evaporation and try to avoid overhead watering as much as possible.
Water the soil slowly and deeply, letting the soil completely absorb as much water as it possibly can. The deep roots will soak up water in the soil lower down. Be careful not to overwater and allow the soil to become too soggy, as this can cause root rot.
When it comes to soil, Amsonia plants aren’t too fazed, as long as it’s well-draining. Sandier soil may require you to water your Bluestars more frequently. And of course, soil that contains a little more clay means that you won’t have to water your Amsonias as often.
Loamy well-draining soil with a slightly acidic to neutral pH is the goal. If you live in warmer climates and struggle with clay soils, soil amendments may need to be added to improve the drainage.
Climate and Temperature
Bluestars are hardy in USDA zones 3-9, depending on the variety. Most grow best in hot and humid climates. They can survive in cooler temperatures, with many surviving freezing winter temperatures too.
Despite this comforting fact for many northern gardeners, however, Amsonias are vulnerable to sudden and drastic temperature changes. As hardy as they are, they still fall prey to sudden heat and cold snaps. Ensure your chosen variety is suitable for your zone to limit potential damage.
They also may need an extra helping hand during winter to get them through the coldest of those frosty months. Mulching with organic mulch, such as straw, will help keep the roots warm during winter. Using mulch is also a great practice during the summer months as it helps keep the soil moist and cool.
Bluestars can thrive in poor quality soil in some pretty tough conditions, but that doesn’t mean you should forgo the routine feeding.
Fertilizing is most important during the first few stages of your Bluestar’s life. When the first few leaves emerge, add a slow-release balanced fertilizer to your soil. This will provide the plant with everything it needs over the flowering season.
Alternatively, start with a nitrogen-rich fertilizer in spring and switch to a fertilizer higher in phosphorus and potassium later on to promote flowering.
The greatest thing about Bluestars is their laid-back nature. They truly require little fuss and worry other than the occasional watering. They need very little maintenance to thrive but will benefit from snip and prune here and there.
The more flowers there are, the happier your garden may seem, but these can weigh your Amsonia down, making them floppy and droopy. Seed pods tend to do the same.
You can either add a stake or hoop to keep them up straight, or you can go ahead and prune away any excess. Think of it more as a grooming session rather than a ruthless prune.
You can easily trim away some flowers and create a stunning Bluestar cut flower bouquet, bringing some of that peace from outside into your home.
Pruning in late fall also adds some winter protection for your Bluestars and promotes healthy growth during spring.
Regular grooming is advised for potted Amsonias to keep them from outgrowing and overwhelming the pot. This promotes fuller growth, even if it’s slightly shorter.
The most common variety is Amsonia tabernaemontana, but there are several varieties of Bluestars each with its own flair.
Amsonia tabernaemontana holds the classic Bluestar look that softens gardens. In many cases, gardeners mistake A. hubrichtii for A. tabernaemontana because of their similarities. A. hubrichtii boasts softer blue flowers and even brighter yellow foliage in fall. It also does not tolerate cold, only growing in Zones 5-8 as opposed to tabernaemontana which grows in Zones 3-9.
Most varieties offer similar design and color to your landscape with minor differences in aesthetics. Take A. ludoviciana for example. It has the same lovely blue flowers, but the undersides of its leaves are fluffy and white.
For those living in drier hotter climates who have fallen in love with Bluestars, the more drought-tolerant A. peeblesii is the perfect variety for you. It boasts slightly narrower leaves than the common Bluestar and has pale blue flowers. A. peeblesii’s fall colors are also more yellow than golden.
A rare variety not native to North America is the A. elliptica. These are found in Japan, China, and even Korea. It’s a smaller variety, only reaching about 15 inches high and its rich blue flowers only measure about half an inch.
Pests and Diseases
When it comes to planting Amsonias, pests and diseases are the least of your worries. These plants are surprisingly resistant to most common pests and diseases, including deer thanks to their slightly toxic sap.
Unfortunately, for those unlucky gardeners, there are a few problems to keep an eye out for, namely rust. This fungal disease is easily identifiable from the rust-colored spots speckling the leaves and stems of your Amsonia. Symptoms also show as dry spots that can be purple, brown, yellow, and even red.
This fungal disease typically causes the flowers and foliage to curl and wither. In severe cases, the plant may lose all its leaves, resulting in stunted growth.
As is the case with all fungal diseases, rust thrives in damp conditions – which is tricky in the case of Amsonias as they love humidity. If you spot these rusty freckles, simply prune away any infected plant limbs and foliage. You can also spray your Amosonias with an organic fungicide as per packing instructions.
Be aware though, that even natural fungicides have some drawbacks. They may not be harmful, but they can deter welcome visitors like pollinators and other beneficial insects that love these plants.
Bluestars add peaceful splashes of blue to any landscape. Their size, fullness, and stunning foliage fill any space, making Amsonias the perfect accent plant.
You can easily recreate Amsonia’s natural carpeted woodland floors through mass planting. Not only does this have a charming appeal, but it’s a look you can achieve over time. Either allow your Amsonias to naturally spread their seeds, or propagate them yourself and plant in randomized groups for a natural feel.
Bluestars don’t have to be planted in the masses to create a spectacle of blue. A single large, healthy Amsonia planted makes quite the statement. Even shorter Bluestars planted in beds under window sills give off classic cottage garden vibes.
The greatest thing about Bluestars is their versatility; you can’t go wrong with planting this plant.
Frequently Asked Questions
Is Amsonia invasive?
Amsonias do have a tendency to spread, but they don’t cannibalize any available space in your garden and aren’t labeled invasive.
How fast does Amsonia grow?
Amsonias grow at a medium rate, reaching maturity in about two to three years. As long as the conditions are favorable, your Bluestars will quickly grow into the peaceful blue spectacle you so desire.
Amsonias thrive in USDA zones 3-11 and can be cold-hardy, tolerating even the coldest winters. Frequent watering, plenty of sunlight, and high humidity levels are all the things Bluestars love.
How deep are Amsonia roots?
Amsonia roots spread deep and wide due to their taproot systems. This system makes them drought tolerant which is a fantastic bonus. But, taproots are also why moving Amsonias is such a difficult task.
Can you divide Amsonia?
Dividing Amosnia is one of three methods you can use to propagate this lovely plant. Dividing the root system is difficult, but not impossible if you have the patience and correct tools.
A sharp shovel will help you get the entrenched Amsonia and its roots out of the ground. A sharp knife or a saw will cut through the thick woody root system and stem with ease.
Is Amsonia poisonous?
Bluestars produce sap that while beneficial in keeping pests away, is toxic to pets and humans. This sap has a milky appearance and is packed with toxic alkaloids that cause irritation to the skin.
While it may not be deathly poisonous to you or your pets, it is advised that you keep cats and dogs away from your Amsonias and wear gloves when handling them.
Is Amsonia deer resistant?
Amsonias are deer resistant, mainly because they produce sap that causes mild irritation in humans and animals. The sap isn’t highly toxic though and if there is a shortage of food, you might find a deer nibbling away at your Bluestars.
Are there other plants with blue flowers that are easy to grow?
Amonsias are laidback plants that offer gardens peaceful splashes of blue during spring with their soft blue star-shaped flowers. Its color-changing foliage makes this plant even more of a spectacle and must-have in any space.
Whether you grow them in mass or as a simple small collection, you can’t go wrong planting this peaceful plant in your garden.