St. John’s wort (sometimes Saint John’s wort or St. Johnswort) has been used medicinally for thousands of years and is the mainstay of any herbalist’s garden. But even if you’re not interested in its medicinal use, it’s an excellent source of nectar for pollinators such as bees, and it looks quite ornamental when fully grown and blooming.
Like many herbs, St. John’s wort can grow exceptionally well in containers.
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Is St. John’s Wort Easy to Grow?
St. John’s wort is an woody, herbaceous weed in its natural habitat, and can survive in a wide range of climates and growing conditions. This makes St. John’s wort one of the easiest flowering herbs to grow.
Growing St. John’s Wort in Containers – Is It Possible?
The hardiness of St. John’s wort also applies to growing in containers.
Not only is St. John’s wort suitable for container gardening, it can thrive in many kinds of pots and even in less-than-ideal conditions it will grow out and produce flowers in a pot.
Moreover, some people prefer growing their St. John’s wort in containers because it can spread very easily through self-seeding and underground stems (similar to mint). Keeping it in a pot will keep the plant under control.
How Long Does It Take to Grow St. John’s Wort?
St. John’s wort typically flowers in the early summer, in June, but can sometimes flower earlier in May or as late as August. If planting from seed, expect St. John’s wort to take at least 90 days to reach maturity.
St. John’s wort grows relatively quickly, growing like a weed in its natural habitat. However, for the flowers (which is what most people grow them for) you may need to wait 90 days, sometimes up to 120 days before being able to harvest them.
When Do You Plant St. John’s Wort?
For best results, sow your St. John’s wort seeds indoors about 6 to 8 weeks before your average last frost date.
St. John’s wort seeds are extremely hardy, being known to survive decades in the ground before sprouting. With this in mind, some people sow in late fall (be sure to sow multiple seeds to guarantee success) allowing the seeds to sprout naturally in the spring. This, however, means your St. John’s wort will sprout later than if you had planted indoors first, meaning you will have to wait longer for its blooms.
How to Plant St. John’s Wort
St. John’s wort has tiny, pill-shaped seeds, so care needs to be taken when planting them.
Sow your St. John’s wort seeds on the surface uncovered or covered with 1/4 inches (6 mm) of potting mix, and keep in a warm location. Start seeds and transplant them to a larger container or direct sow in its final container or in the ground. Keep your seeds moist but not soggy until they germinate, then put them under grow lights or in a sunny, south-facing window until transplanting.
St. John’s wort is one of those plants whose seeds germinate more successfully with light. However, you don’t necessarily need a special grow light to sprout them, just spread the seeds on the surface or very lightly cover with potting mix and keep in a room with some ambient light.
How Big Does St. John’s Wort Get?
If given enough space to grow, St. John’s wort can get up to 3 feet (91 cm) tall with a 2-foot (61-cm) spread.
One important thing to note is that St. John’s wort spreads via underground stems, similar to how mint grows, so while an individual plant might be 2 feet across, St. John’s wort will eventually spread to fill up any size container or garden bed you plant it in.
If constrained to a smaller container, St. John’s wort will stay smaller, less than 2 feet tall.
Container Size for St. John’s Wort
St. John’s wort can adapt to different sizes of pots, even growing when constrained in a small container.
For large-sized St. John’s wort, plant in at least a 3-gallon (11 L) container that is at least 12 inches (30 cm) deep. However, St. John’s wort will thrive in smaller containers but won’t grow as large.
St. John’s wort has a strong, deep taproot, even though the plant itself usually gets no more than 3 feet (91 cm) tall. However, this taproot only grows deeply when the seeds are direct sown in the ground, not transplanted or grown in containers (unless you have a very deep container).
An option if you have the space is to direct sow in the final container size indoors instead of starting in a seed tray or small pot and transplanting to a larger pot. Nevertheless, this isn’t really necessary since St. John’s wort is a hardy plant that is used to growing in rough terrain.
St. John’s Wort Water Requirements
St. John’s wort thrives under many environmental conditions, and is very forgivable to beginner growers after plants are established.
Keep soil moist for young St. John’s wort plants; water less frequently after plants are established, especially after their first year.
St. John’s wort should be planted in well-drained, coarse soils, as it does not grow well in very muddy or heavy clay soils. In a container, use well-draining potting mix.
Is St. John’s Wort Drought Tolerant?
Well-established, mature St. John’s wort plants are quite drought tolerant, and some growers note that older plants grow better under dry conditions, watering just often enough to keep them from wilting.
Does St. John’s Wort Need Full Sun?
A lot of herbs, medicinal and culinary, prefer full sun. However, St. John’s wort isn’t too picky.
St. John’s Wort grows best in partial shade to full sun. Too much direct sun can lead to leaf scorch while too much shade will slow its growth and lead to leggy plants.
One of the best advantages of growing in containers is that you can move your plants around depending on the weather conditions. The best location for St John’s wort grown in containers is somewhere where it will get direct sun in the morning and some shade in the hot afternoons. An example would be along an east-facing fence or on the east side of a row of taller vegetables, herbs, or shrubs. You can even plant them around an arbor where they can get some shade in different parts of the day.
Is St. John’s Wort a Perennial or Annual?
St. John’s wort is a perennial, but is grown as an annual in northern climates, tolerating mild frosts, although it can sometimes be hardy down to -10°F (-23°C).
If you live in an area with freezing winters, you can either save the seeds or make cuttings for next year, or you can protect your St. John’s wort so it can grow back the following year.
How Do You Winterize St. John’s Wort?
There are two approaches to overwintering St. John’s wort: winterizing with heavy mulch or overwintering indoors.
Whether you’re growing in containers or in the ground, applying a thick layer of mulch (wood chips, pine needles, leaf mulch, straw, etc.) will help protect the crown. In addition, wrap your container with garden fleece or burlap to insulate the sides, since soil in containers get colder and freeze more easily. For added protection, cover your St. John’s wort with garden fleece as well.
Pro-Tip: You can also move your container against a south-facing wall where the microclimate is a few degrees warmer due to the sun and radiating heat from your home.
Alternatively, you can bring your St. John’s wort indoors, such as in an unheated garage or shed. In this case, mulching and extra protection isn’t necessary if it rarely gets below freezing.
You do not need to prune St. John’s wort before overwintering.
When Should I Cut Back St. John’s Wort?
The best time to prune St. John’s wort is in early spring before new growth begins. Flowers bloom off new branches, so cutting back your St. John’s wort by about 1/3 of the plant’s height every spring is recommended.
There are a couple reasons to cut back your St. John’s wort. First is to encourage new growth and flowers. But the other reason you should cut it back is to keep its growth under control as it can spread and take over a garden bed if left unchecked.
Should I Deadhead St. Johns Wort?
One strategy when growing multi-stemmed flowering plants is to remove the dead flowers (deadheading) to encourage new growth.
After St. John’s wort begins blooming in early summer, it will continually produce new flowers until fall. To encourage more blooms, prune off wilting or dead flowers.
Deadheading St. John’s wort also keeps your plant more tidy, as it can quickly turn into a dense shrub. You can pick off individual dead flowers or cut back entire flower clusters.