Atlantic St. John’s-wort (Hypericum tenuifolium)

Atlantic St. John’s wort is distinguished by its slender, thread-like leaves and prolific bright yellow flowers. These delicate blooms often signal the start of summer in its native habitat, flourishing under ample sunlight. Well-suited to rocky or sandy soils, Atlantic St. John’s wort’s hardy nature allows it to thrive in environments that challenge less adaptable species. Its compact growth habit renders it a favored choice for ornamental garden borders and rockeries.

I. Appearance and Characteristics

Hypericum tenuifolium, known as Atlantic St. John’s-wort and sandhill St. John’s-wort, is a species of flowering plant in the St. John’s wort family, Hypericaceae. It is native to the Southeastern United States.

Atlantic St. John’s-wort is a small, spreading shrub, growing 10–50 cm (3.9–19.7 in) tall and forming mats. The leaves are very narrow, hence its name tenuifolium (from Latin tenuis ‘thin’, and folium ‘leaf’), and are only 0.4–0.8 mm (0.016–0.031 in) broad and 4–11 mm (1⁄8–3⁄8 in) long, with rounded tips and revolute margins. The flowerheads are narrowly cylindric, producing 1-7 flowers. Each flower is 10–14 mm (3⁄8–1⁄2 in) broad with 5 sepals, 5 bright yellow petals, and 50-90 stamens. The ovaries are three-parted, forming cylindric capsule fruits. It flowers in the summer, typically June through September, but sometimes as late as December.

Atlantic St. John's-wort (Hypericum tenuifolium)

II. How to Grow and Care

Sunlight

Atlantic St. John’s wort needs sufficient sunlight but doesn’t tolerate direct light. Grow the plant in the shade of other plants or on a balcony away from strong, hard light. Expose it to more sunlight in the spring and fall to help it grow, but in the summer, place the potted plants in half-shaded places and mist them with water to cool the temperature and increase humidity. Otherwise, symptoms like drying leaf tips may appear.

Temperature

Plants of the Hypericum genus are widely distributed. They like warm, moist environments; the best temperature range for the plants is 20 to 26 ℃, but they can tolerate temperatures as low as -10 ℃. They require little water and endures drought, but don’t tolerate waterlogged soil. Avoid watering so frequently that the soil gets waterlogged.

Watering

Atlantic St. John’s wort can withstand drought but is intolerant of waterlogged soil. In the first year after planting, about 2.5 cm of water every week will be enough. In areas with plentiful rain, no additional watering is needed. From the second year on, atlantic St. John’s wort doesn’t need any additional watering, as normal precipitation will meet its needs for water. If over-watered, its roots are likely to rot due to waterlogging, and leaves will wither and dry up.

Soil

Atlantic St. John’s wort can adapt to a wide range of soil types. It grows well in most common soils (except for heavy clay) and prefers sandy loam with good drainage. A slightly acidic loam with a 5.5-7.0 pH value is ideal. Atlantic St. John’s wort is tolerant of barren soil and drought, but if the soil can’t drain water well, waterlogging can cause the roots to rot.

Fertilizing

Atlantic St. John’s wort requires very little fertilizing. Usually, no additional fertilization is needed after the initial planting, unless obvious symptoms of slow growth appear. If that happens, apply some low-concentration balanced compound fertilizer (10-10-10 NPK ratio).

Planting Instructions

Plant Atlantic St. John’s wort in the early spring or early fall. Choose a cool, shaded place, such as within tree shade. Remember to clear the soil first and remove weeds. Dig a planting pit slightly shorter than the diameter of the root ball and 3 times wider. If you’re planting more than one sapling, avoid planting them too close, or low light and poor ventilation may result in powdery mildew. P

ile some soil around the root collar (the juncture of trunk and roots) to form a gentle slope, and this helps disperse water. After planting, press the soil firmly and water thoroughly. Note the distance between each

Some plants in the Hypericum genus have subterraneous rhizomes that tend to expand in all directions. To prevent excessive expansion, it’s a good idea to fence the planting spots or set brick perimeters around them to control their growth.

Pruning

Atlantic St. John’s wort doesn’t need much pruning. To promote more lush growth, trim 1/5-1/4 of the total branch length by the end of spring or early summer, which promotes new branches to sprout. Atlantic St. John’s wort buds and leaves both grow in pairs. Generally speaking, cutting one branch off promotes the pair of buds beneath the incision to develop into two branches.

For Atlantic St. John’s wort with robust growth and branches crossing inward, winter is the time for an overall pruning. As perennial herbaceous plants, you may just clip them flat with a sickle and they will revive. Atlantic St. John’s wort has a short life span, so you can also consider getting new seedlings to replace the old ones once they start to decline.

Propagation

Atlantic St. John’s wort can be propagated by seeding, cuttage, or plant division. To sow seeds yourself, sow them in a sand bed. Dust a thin layer of soil on them, water once, and sprout the seeds in temperatures of 10 to 12 ℃. Keep the potting soil moist. Transplant seedlings when they grow to 5 to 10 cm tall.

For St. John’s worts with dense branches, propagation is usually performed at the end of summer by soft-branch cuttage. Choose some robust, soft branches that sprouted in the current year. Cut 10 to 15 cm-long from the tip, making sure to keep at least 2 full leaves on each branch. Insert the cut branches into the soil and keep half the length aboveground. Keep the soil and the environment moist. When the seedlings reach 20 cm tall, transplant to pots. Seedlings need to grow to 70 cm tall to move outdoors or wait until the end of the next summer.

III. Uses and Benefits

Atlantic St. John’s wort can be used as a foundation plant, along a border or edge, or in a mass planting.

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