Asthma Plant (Euphorbia hirta)

Asthma-plant (Euphorbia hirta) is a ground-hugging spurge weed whose branches can grow to 61 cm long. It blooms from summer through early fall, dying off after the first frost. A milky sap will seep from broken stems or leaves. It can be a nuisance weed that reproduces rapidly.

I. Appearance and Characteristics 

Euphorbia hirta (sometimes called asthma-plant) is a pantropical weed, originating from the tropical regions of the Americas.

This erect or prostrate annual herb can grow up to 60 cm (24 in) long with a solid stem that is furnished with many yellow to reddish coarse hairs, and produces an abundant white latex. There are stipules present. The leaves have an oblique base and are simple, elliptical to slightly rhombic, hairy (on both upper and lower surfaces but particularly on the veins on the lower leaf surface), with a finely dentate margin, the veins upperside being deep-set and conspicuous on the underside, and the leaf surface somewhat leathery. Leaves occur in opposite pairs on the stem. The flowers are unisexual and found in axillary cymes at each leaf node, held as dense balls of flowers and fruit capsules usually close to the stem, the flower glands with tiny white/pinkish petal-like appendages. The fruit is a capsule with three valves (creating 3 sides), uniformly appressed hairy, containing tiny (0.7–0.9 mm), oblong, four-sided orange to pink or red seeds. It has a white or brown taproot.

II. How to Grow and Care

Sunlight

Asthma-plant thrives in conditions of full sun, exposing it to abundant light that promotes vigorous growth and optimum health. The high light intensity facilitates robust photosynthesis, necessary for the production of energy in asthma-plant’s cellular processes. While asthma-plant tolerates a wide range of light intensities, any significant deviation from full sun, especially lower light levels, could lead to reduced growth rates and potential health issues such as diminished flowering or foliage vitality. Due to these preferences, asthma-plant is best sited in outdoor locations where direct sunlight is ample for most of the day. Any adaptive traits to light exposure would assist asthma-plant in managing less than ideal conditions, aiding survival but not necessarily optimal health.

Temperature

Genus Euphorbia is very large and diverse, so its different species can be found in various habitats, but the majority are well-adapted to a temperature range of -29 to 4 ℃. Many spurges, in spite of having succulent leaves, cannot handle long periods without moisture and need to be watered weekly during hot summer days. Some cactus-like species are well adapted to high temperatures and prolonged dry periods, but most species used for landscaping and decorative gardening require more moisture for proper development.

Watering

Asthma-plant thrives in its native tropical environments where consistent moisture and high humidity are the norms. This species has adapted to these conditions with a moderate drought tolerance, balancing its need for regular hydration without becoming waterlogged. For optimal growth, asthma-plant should be watered every week. As an herbaceous plant often grown indoors due to its air-purifying qualities, asthma-plant benefits from soil that mimics its tropical origins—well-draining yet consistently moist, avoiding extremes of drought or saturation.

Soil

Spurges aren’t picky when it comes to soil type. They can grow in a variety of soils. Some species of Euphorbia can even thrive in nutrient-poor soils, requiring only that the soil be well drained. If the soil is full of moisture and is prone to water retention, it will most likely cause root rot.

Fertilizing

Asthma-plant doesn’t require large amounts of fertilizer for normal growth and development. In fact, very little fertilizer is required. As mentioned earlier, some species can thrive even in very poor soils, as long as those soils are well drained. Fertilizer should only be applied when the plants start showing nutrient deficiency symptoms on lower leaves. When the lower leaves turn yellow, it is time to add half-strength liquid fertilizer to the soil. That will keep the plant well fed for several months.

Planting Instructions

Dig a hole twice as wide as the plant’s root ball before planting. Then, turn the container with asthma-plant upside down and let the plant slowly fall into your hands. Place the plant upright in the hole and slowly fill in around the roots with loose and fertile potting mixture, adjusting the planting depth until it is just right. Water it once. Do not overwater, as standing water is not good for the plant.

Pruning

In early spring, if there are any damaged stems, they need to be removed to keep the plants healthy and to optimize their nutrient management. It is advised to cut back a certain number of stems after blooming in order to stimulate consistent flowering and growth of new foliage. When cutting a stem, cut at the stem’s base. It is very important to use gloves while handling and pruning asthma-plant, because their tissues contain milky-white latex sap which is poisonous and can irritate the skin.

Propagation

Asthma-plant can be successfully grown from seeds, but the seeds are rarely commercially available because they are difficult to germinate and stay viable only for a short period of time. Asthma-plant is most commonly propagated via cuttings.

It is important to wear gloves while working with asthma-plant cuttings and to clean the pruning shears thoroughly after pruning, so that any unwanted contact with the sap is avoided. Before planting, it is necessary to leave the cuttings to dry for 2-3 days. This will prevent rot from developing and enable proper formation of the callus tissue. It is advised to plant the cuttings in a soilless medium, such as peat moss, because it provides an optimal environment for proper root development.

Cuttings should be misted regularly, and the pots in which they are planted need to be wrapped in either foil or a plastic bag to preserve moisture. The bag or foil needs to be removed for two hours each day to provide sufficient air and to prevent excess moisture in the medium. If this step is skipped, molds and rots can easily develop and damage the health of the young, sensitive cuttings. When the cuttings develop a root system, they are ready to be transplanted into soil.

III. Harvesting and Storage

Some species of Euphorbia can be cut for fresh flowers or foliage, such as snow-on-the-mountain (Euphorbia marginata), Euphorbia fulgens and Euphorbiaformosana. When harvesting cuttings, remember to wear gloves, as the sap can be irritating to the skin. It can be cut from the base of the stem. Soak the end of the cutting in hot water for 10 seconds to stop the milky sap from oozing. The vase life for the cutting will be about 5-7 days, and some flower food can extend its life.

When the fruits of Euphorbia plants are ripe, they burst and scatter the seeds over a large surface area. In order to harvest all the seeds, the individual fruits or the entire plant must be wrapped in in nylon, gauze, or similar material before the ripe fruit bursts and releases the seeds.