Phototoxic Plants: Don’t Touch When the Sun Shines!

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Giant hogweed (Heracleum mantegazzianum) is a good example of a phototoxic plant: don’t handle it on sunny days! Source: &, montage:

With the outdoor gardening season starting up, it may be useful to remind gardeners (and hikers!) to avoid, if possible, any contact with phototoxic plants, present in both our gardens and in fields and forests, or at least, to avoid them on sunny days.

20180416B Vincent, WC.jpgA phototoxic plant is one that causes a cutaneous reaction in humans or animals when there has been contact with the skin followed by exposure to the sun. You only have to brush against one to be affected, although actually handling the plant will make things worse. So, unlike plants that cause skin reactions under any circumstance, such as poison ivy (Toxicodendron radicans) or stinging nettles (Urticaria spp. and Laportea spp.) and where the reaction can therefore take place at any time, even at night, phototoxic plants only wreak havoc on beautiful sunny days … when gardeners and hikers are most likely to be outdoors. And unlike allergic reactions, there is no need to have been exposed to the plant in the past.


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Wild parsnip (Pastinaca sativa) is a common field weed that is a frequent cause of phytotoxicity. Source: Westdelta,

The main chemical compounds that cause phototoxic reactions are furocoumarins, produced by plants to protect themselves from predators. They are mainly found in two plant families: the Apiaceae (ombellifers) and the Rutaceae (the orange family). Some are wildflowers or weeds, such as giant hogweed (Heracleum mantegazzianum) and wild parsnip (Pastinaca sativa), while others are garden plants, such as rue (Ruta graveolens), a medicinal and edible herb, and gas plant (Dictamnus albus), an ornamental perennial.

Susceptibility to phototoxic plants (called photosensitivity) varies greatly from one individual to the next. Some people can manipulate many phototoxic plants with no reaction whatsoever while others are only affected quite lightly, with a reaction the equivalent of a mild sunburn. However, in other people, the affected skin darkens or becomes covered in painful blisters that may even leave permanent scars. Extremely sensitive people sometimes end up in the hospital! Children tend to be more photosensitive than adults, but, as with allergies, some adults become more seriously affected after repeated contacts.

Which Plants to Watch Out For


Rue (Ruta graveolens), an herb, is a frequent cause of phytotoxic reactions in home gardens. Source:

Phototoxic plants were not all created equal. Some are much more dangerous than others. Giant hogweed is considered extremely phototoxic and most people need to avoid it, but some people react to plants that are rarely a problem for the average human, such as wild carrot (Daucus carota), a weed common in fields almost everywhere and to which only a small minority of people react. Several common garden herbs and even a few everyday vegetables can cause phototoxic reactions in very sensitive people, especially when they handle their foliage, although furocoumarins can be present in some roots as well. It you know you’re sensitive to furocoumarins, it might be wise to touching anise, angelica, celery, carrots, coriander, dill, fennel, lovage, parsley and – above all! – rue (about a third of all people are sensitive to the latter). Among tropical edibles, reactions to limes, lemons and sour oranges are not rare and some people develop lip blisters from eating figs (from another family, the Moraceae). It’s perhaps best to eat these in the shade or at night!

Be Prepared


This worker is collaborating in a campaign to eliminate giant hogweed. You should dress similarly if you have to handle phototoxic plants. Source:

Even if you have never reacted in the past to plants known to be very phototoxic, such as giant hogweed and wild parsnip, it is always best to avoid contact with these plants, especially on a sunny day. Even on a gray one, it’s always wiser to wear gloves and long sleeves and pants if you’ll be handling potentially phototoxic plants … and to wash well with soapy water once back at home!20180416F & .jpg


2016: The Year of the Carrot


20160102AEach year the National Garden Bureau declares a “year of” that features four plants: one vegetable, one perennial, one annual, and for the first time in 2016, one bulb. Let’s first take a look at the vegetable of the year, the carrot. I’ll discuss the other laureates in upcoming blogs.



Wild carrot root.

The wild carrot (Daucus carota) is a biennial of the Apiaceae family. It was originally native to temperate regions of Eurasia, but has since spread extensively, naturalizing in many parts of the world, including in North America where it is a common field and roadside weed.


Umbel of white flowers.

The first year the wild carrot forms a rosette of finely cut leaves as well as a long tuberous tap root. The root is normally white inside but purple in parts of its range. The second year the plant flowers, producing a 1 to 2 foot (30 to 60 cm) high stem bearing an umbel of white florets (rarely pink), often with one red flower in the center to better attract pollinators. At maturity, the umbel dries up and drops to the ground where, aided by its rounded shape, is pushed by the wind, rolling away like a tumbleweed to ensure a wide distribution of its seeds.

The root of the wild carrot is edible at first, although bitter, but quickly becomes too tough and stringy for human consumption. Moreover, originally humans used to eat the foliage rather than the root, much like we use parsley (Petroselinum crispum), actually a close relative, today. The aromatic seeds were also harvested and eaten.

It is believed that domestication of the carrot took place in Persia (now Iran and Afghanistan) about 5000 years CE. The domesticated form is treated as a subspecies under the name D. carota sativus. Through generations of selection, the original tough root has become softer and sweeter without a woody core and much of the bitterness of the original root is now a thing of the past. An edible root that might well be a carrot was mentioned in Roman writings in the 1st century CE, but it seems to have disappeared from Europe shortly thereafter and was only reintroduced by the Moors in the 8th and 10th centuries. The carrot then reached China in the 14th century. At that time, carrot roots were white, purple, red or yellow.

It wasn’t until the 17th century that the orange carrot as we know know it was first developed in the Netherlands. Its intense coloration is due to the great concentration of beta carotene it contains.

Growing Carrots


Sowing carrot seeds.

Today we grow carrots as an annual, harvesting it the first year, so we never see it bloom. Sow it as soon as the soil warms up in the spring. In cold climates, usually only one sowing is carried out per year, because carrots mature very slowly, taking pretty much an entire growing season to reach their maximum size, but gardeners in mid climates can do successive plantings. Cold-climate gardeners can also try a second sowing if they decided to harvest baby carrots (immature ones) only.


Rocky and heavy soils give forked roots.

Soil quality is of utmost importance important in growing carrots, although it is quite adaptable when it comes to soil acidity: a pH of anywhere from 5 to 7.0 is fine. It’s when it comes to soil structure that the carrot needs special attention. For long, straight carrots, the soil should be sandy loam. Avoid rocky soils. If not, when the root encounters even a pebble, it will start to fork. Carrots are not a good choice for heavy clay soils either: they tend to grow slowly and irregularly in soil that dense. To obtain good roots in clay soil, ideally you’d have to mix in a abundant amount of organic material to loosen it up. However avoid both fresh manure and fresh compost, as well as nitrogen-rich fertilizers, as they also stimulate the formation of forked roots.

If your soil is clay or rocky, another option is to grow round carrots: since their root is short and rounded, they aren’t affected by poor quality soil.

You can also grow carrots in container gardens. You’ll need a pot at least 1 foot (30 cm) deep to allow for reasonable root development… or grow round carrots or baby carrots.

Sow the seeds 3/16 inches (5 mm) deep, covering them with loose soil or sand (never clay, otherwise the soil may become caked, preventing the fragile seedlings from emerging). Germination will take 1 to 3 weeks. The young seedlings grow more slowly than most other vegetables, especially early in the season. If you grow them in rows, leave 12 to 16 inches (30 to 40 cm) between the rows. In square foot gardening, sow 16 plants per 1 foot (30 cm) square. In the French intensive method, sow loosely, then thin to about 2 to 3 inches (5-8 cm) apart in all directions. (You can harvest and eat the young carrots you thin out.) When plants are about 2 inches (5 cm) high, mulch to prevent the root’s shoulder (top section) from turning green due to sun exposure. This will also do deter carrot flies and will help keep the soil evenly moist, something carrots will appreciate.

Carrots can be harvested at any stage of their development. Round carrots mature in about 50 to 60 days, most standard carrots in 75-120 days, depending on cultivar. Carrots can be left in the ground well into the fall, allowing you to harvest them as needed. Cooler fall temperatures not only encourage a sweeter taste, but harden the roots off so they will store better.

To store carrots, remove the tops and clean well. Carrots will keep for 2-4 weeks in the refrigerator and most of the winter in a root cellar, layered in sand. Don’t store them near apples or pears: they give off ethylene, a gas that makes carrots bitter.

Carrot tops are also edible. They are delicious cooked, in soups, in quiches or added to mashed potatoes. They can also be used as a condiment, finely chopped, just like you’d use parsley.


The carrot is a very nutritious vegetable, containing antioxidants, anti-inflammatories, vitamins (mostly C, K and all the B vitamins except B12), lots of fiber, and an abundance of minerals, especially calcium, magnesium, potassium and iron. However it is primarily recognized for its exceptional richness in beta-carotene (which the body converts into vitamin A). One 1/8 cup (25 g) meets more than half of an adult’s daily requirement of vitamin A.



Carrots come in a wide range of colors.

There are hundreds of carrot varieties in a wide range of shapes and colors.

In North America, the following system is often to classify carrots:

Chantenay: conical, rather short root, wide neck, rounded tip.

Danvers: thick, cylindrical root, pointed tip.

Imperator: long, narrow and tapered root, pointed tip (the typical supermarket carrot).

Nantes: cylindrical (hot dog-shaped), clearly rounded tip.

Round: globular, for early harvests.

Fun Facts About Carrots

You need to sow carrots directly in the garden, as transplants won’t form the carrot’s famous tuberous root.

True enough, carrots contain carotene, a precursor of vitamin A, and vitamin A is important in eye health, but the belief that eating carrots significantly improves night vision is strictly an urban legend.


Longest carrot competition.

The world’s longest carrot measured 20 feet 5.86 inches (6.245 m). The world’s heaviest carrot weighed a whopping 22.44 pounds (10.17 kg).

Eating too many carrots will turn the skin orange, an effect that disappears after a few weeks if you cut back on their consumption.

You can leave winter carrots in the ground all winter for a spring harvest.

You can’t grow carrots in hydroponically because in an aqueous environment, they form only fine roots, leaving you nothing to harvest but the foliage.

There are carrot varieties that are resistant to carrot fly, like ‘Resistafly’ and ‘Fly Away’. They contain little or no chlorogenic acid, the component whose strong scent would otherwise attract to the fly to its host.

Bagged, peeled “baby carrots” found in supermarket are not really baby carrots, but rather standard length carrots that have been cut to fit the desired shape.

There you go! All you wanted to know about carrots (and probably many more!). Let’s celebrate the Year of the Carrot together by sowing our own carrots this spring!