Foxglove is a flowering plant in the genus Digitalis, best known for its tall spikes of bell-shaped blooms and its role as the original source of a widely used heart medication. It grows 2 to 5 feet tall, thrives in gardens across much of the United States, and is highly poisonous if eaten. Whether you’ve spotted one in a garden, on a hike, or in a seed catalog, here’s what you should know about this striking but dangerous plant.
What Foxglove Looks Like
The most common species, Digitalis purpurea, belongs to the plantain family (Plantaginaceae). In its first year, foxglove stays close to the ground, forming a tight rosette of large, coarse leaves up to a foot long. The leaves are simple and lance-shaped with prominent veins, covered in fine gray-white hairs on top and woolly underneath. They feel distinctly velvety to the touch.
In the second year, the plant sends up a tall, upright flower stalk from the center of that leafy base. The stalk produces a dramatic one-sided column of large, drooping, tubular flowers. Each bloom is funnel-shaped and bell-like, typically purple or pink on the outside, with a whitish interior dotted with dark purplish spots. Those interior markings act as guides for bees, which crawl inside the tubes to pollinate. Cultivated varieties also come in white, yellow, peach, and rose.
Biennial Life Cycle
Foxglove is technically a biennial, meaning it completes its life cycle over two growing seasons. The first year is all foliage: that low rosette of fuzzy leaves. The second year brings the flower stalk, seed production, and then the plant dies. Some varieties self-seed so freely that they appear perennial, with new plants filling in every year. It’s hardy in USDA zones 4a through 9b, which covers most of the continental United States.
Foxglove prefers partial shade and moist, well-drained soil. It naturalizes easily in woodland edges and disturbed areas. In California, it’s classified as a limited invasive species, meaning it can persist locally and become problematic in certain ecosystems, though its ecological impact is considered minor statewide.
Why Every Part of It Is Toxic
All parts of foxglove, including the leaves, flowers, stems, and seeds, contain compounds called cardiac glycosides. These chemicals directly affect how the heart beats. If ingested, they interfere with a pump on the surface of heart muscle cells that regulates sodium, potassium, and calcium levels. The result is a dangerous buildup of calcium inside heart cells, which can force the heart into abnormal rhythms.
Symptoms of foxglove poisoning include nausea, vomiting, weakness, fatigue, and stomach pain. The more serious effects are cardiac: irregular heartbeat, dangerously slow heart rate, and various types of heart block where electrical signals through the heart are delayed or interrupted. Ingesting even a small amount of the plant can be fatal. Foxglove leaves have been mistakenly eaten after being confused with borage or comfrey, two edible plants with somewhat similar-looking foliage. The key differences are foxglove’s distinctly velvety texture, its gray-white hairy surface, and its prominent leaf veins.
Pets are also at risk. Dogs, cats, horses, and livestock can be poisoned by eating any part of the plant or even drinking water from a vase that held cut foxglove flowers.
From Folk Remedy to Modern Heart Drug
Foxglove’s medicinal properties were known in folk medicine long before they were studied formally. In 18th-century England, a physician named William Withering learned from a local herbalist that foxglove could treat “dropsy,” a term for the severe fluid retention caused by what we now call congestive heart failure. In 1785, Withering published the first systematic report on using foxglove leaves to treat the condition, carefully documenting dosing and side effects. That publication became a landmark in pharmacology.
The active compound eventually isolated from the plant, digoxin, remains in clinical use today. It’s FDA-approved for treating mild to moderate heart failure in adults and for controlling heart rate in chronic atrial fibrillation, a condition where the upper chambers of the heart beat irregularly and too fast. In controlled pharmaceutical doses, digoxin does exactly what makes the raw plant so dangerous: it strengthens heart contractions and slows heart rate. The difference between a therapeutic dose and a toxic one is extremely narrow, which is why patients on digoxin require regular blood monitoring.
Interestingly, the pharmaceutical version of digoxin is extracted from a related species, Digitalis lanata, rather than the common foxglove found in most gardens. But both species contain the same class of compounds.
Growing Foxglove Safely
Foxglove is one of the most popular cottage garden plants, valued for its height, its ability to thrive in shade, and the vertical drama its flower spikes add to a border. If you choose to grow it, plant it where children and pets won’t have unsupervised access. Wear gloves when handling it, since the cardiac glycosides can be absorbed through skin in large enough quantities to cause irritation, and wash your hands afterward.
Because it’s a biennial, you’ll want to plant seeds or starts two years in a row to ensure blooms every season. Let the flower stalks go to seed at the end of the season if you want the plants to naturalize, or deadhead them to prevent spreading. In the right conditions, foxglove will reseed itself and return reliably year after year without much effort on your part.