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

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20180416F wagwalking.com & www.handinorme.com .jpg

Giant hogweed (Heracleum mantegazzianum) is a good example of a phototoxic plant: don’t handle it on sunny days! Source: wagwalking.com & http://www.handinorme.com, montage: laidbackgardener.blog

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.

Whodunit?

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

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

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

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

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

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 wagwalking.com & www.handinorme.com .jpg

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Only January, Yet Already Time to Sow Seeds?

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20180103 ENG worldartsme.com, rdkate.blogspot.ca & mzayat.com.jpg

It’s only January! Surely it’s too soon to sow seeds? Source: worldartsme.com, rdkate.blogspot.ca & mzayat. com

The new year has barely begun, yet now and over the coming month it’s already time to start certain seeds indoors.

This is a very select group of especially slow-to-mature plants. January is far too early for most seeds (think March or April instead), but you need about four to five months of indoor culture to bring the following plants to the right state of growth for outdoor planting.

  1. Agastache (Agastache foeniculum)
  2. Datura (Datura metel)
  3. Fairy Snapdragon (Chaenorrhinum origanifolium, syn. glaerosum)
  4. Lisianthus (Eustoma grandiflora)
  5. Spike dracaena or cabbage palm (Cordyline australis, syn. indivisa)
  6. Tritome (Kniphofia )
  7. Tuberous Begonia (Begonia × tuberhybrida)

No Easy Feat!

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Artificial light is almost essential for seeds started in January. Source: laidbackgardener. blog

Starting seed in January in the Northern Hemisphere is not simple. The days are short, the sun is weak and, in many areas, the weather is gray more often than sunny, meaning light is seriously lacking. Also, temperatures in front of the average windowsill are cool, yet almost all seeds need warmth—and fairly even temperatures—to germinate well. As a result, you pretty much have to start these under artificial lights, such as fluorescent or LED plant lights, and in the warmest part of your home.

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Germinate the seedlings under glass, possibly over a heating pad, as above. Source: www.amazon.fr

Always start winter-sown seeds “under glass” (under some sort of transparent covering) to maintain high humidity and stable temperatures and in a room that is at least moderately warm (72 to 75˚ F/21 to 24˚ C) or place the seed containers on a heating pad (one specifically designed for plants). Use a timer to set the day length of your lamp at 14 hours to simulate the long days of summer and place the containers of freshly sown seeds about 6 to 12 inches (15 to 30 cm) below the lamp. Now, wait patiently for germination to occur. (One reason that certain seeds need early sowing is that they are slow to germinate.)

Seeds That Require a Cold Treatment

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Many tree, shrub and perennial seeds need a cold treatment before they will germinate. Source: laidbackgardener. blog

January (or December or February) is also a good time to start seeds that need a cold treatment (cold stratification) to germinate well. This group includes most trees and shrubs from cold and temperate climates, but also many perennials and even a few annuals.

These seeds will not germinate until they have received a given number of days of cool, moist conditions, from as little as one or two weeks to four months or more, information you would (hopefully) find on the seed pack.

The number of weeks given is the minimum requirement for that species, but there is no maximum. So, if you keep seeds that need, say, a two-week treatment in the cold for two months, that’s not a problem. That’s nice to know, because the information on the minimum cold treatment for seed X is not always available, especially for seed you harvested yourself. If you don’t know, I suggest giving seeds of perennials a six to eight-week cold treatment: that’s usually enough. For trees and shrubs, I’d recommend three months.

Simply sow these seeds in a container as you would any other, then seal them inside a clear plastic bag and pop them into the refrigerator or cold room for at least the minimum number of weeks. Afterwards, move them to a warm, well-lit spot, on a windowsill or under lights, for germination to start.

100 Seeds That Need a Cold Treatment

Here are 100 plants that germinate best with a cold treatment (there are thousands of others!). Check the seed envelope or the seed supplier’s web site for more information.

  1. Abies (fir)
  2. Acer (maple, mosts species)
  3. Aconitum (aconite)
  4. Alchemilla (lady’s mantle)
  5. Allium (ornemental onion)
  6. Amelanchier (serviceberry)
  7. Aquilegia (columbine)
  8. Asclepias (milkweed, some species)
  9. Astrantia (masterwort)
  10. Baptisia (false indigo)
  11. Buddleia (butterfly bush)
  12. Caltha (marsh marigold)
  13. Caryopteris (bluebeard)
  14. Cercis canadensis (redbud)
  15. Chelone (turtlehead)
  16. Cimicifuga (bugbane)
  17. Clematis (clematis)
  18. Cornus (dogwood)
  19. Corydalis (fumitory)
  20. Delphinium (delphinium)
  21. Dicentra spectabilis, now Lamprocapnos spectabilis (bleeding heart)
  22. Dictamnus (gas plant)
  23. Dodecatheon (shooting star)
  24. Echinacea (purple coneflower)
  25. Eremurus (foxtail lily)
  26. Eryngium (sea holly)
  27. Eupatorium (Joe Pye weed)
  28. Filipendula (meadowsweet)
  29. Forsythia (forsythia)
  30. Fragaria (strawberry)
  31. Fuchsia (fuchsia)
  32. Gentiana (gentian)
  33. Geranium (perennial geranium, cranesbill)
  34. Goniolimon (German statice)
  35. Helianthemum (rock rose)
  36. Helianthus (perennial sunflower)
  37. Heliopsis (false sunflower)
  38. Helleborus (Christmas rose)
  39. Hemerocallis (daylily)
  40. Heuchera (coral bells)
  41. Hibiscus moscheutos (perennial hibiscus)
  42. Hypericum (St. John’s wort)
  43. Iberis (perennial candytuft)
  44. Ilex* (holly)
  45. Incarvillea (hardy gloxinia)
  46. Iris (iris, many species)
  47. Kirengeshoma (waxbells)
  48. Knautia (knautia)
  49. Lathyrus (perennial sweet pea)
  50. Lavandula (lavender)
  51. Leontopodium (edelweiss)
  52. Lobelia (hardy lobelia)
  53. Lonicera (honeysuckle)
  54. Macleaya (plume poppy)
  55. Magnolia* (magnolia)
  56. Malus (apple, crabapple)
  57. Mazus (creeping mazus)
  58. Mertensia (Virginia bluebells)
  59. Muscari (grape hyacinth)
  60. Myrrhis odorata (sweet cicely)
  61. Nepeta (catmint)
  62. Oenothera (evening Primrose)
  63. Opuntia* (beavertail cactus)
  64. Paeonia* (pivoine)
  65. Penstemon (beard-tongue)
  66. Persicaria (fleeceflower)
  67. Persicaria orientalis, syn. Polygonum orientale (kiss-me-over-the-garden-gate)
  68. Phlox (phlox)
  69. Physalis (Chinese lantern)
  70. Picea (spruce)
  71. Platycodon (balloon flower)
  72. Primula (primrose)
  73. Pulsatilla (pasque flower)
  74. Quercus (red and black oaks)
  75. Ranunculus (buttercup)
  76. Ratibida (prairie coneflower)
  77. Rosa (rose)
  78. Rudbeckia (black-eyed Susan)
  79. Sambucus (elderberry)
  80. Sanguinaria (bloodroot)
  81. Sanguisorba (burnet)
  82. Saponaria (soapwort)
  83. Saxifraga (saxifrage)
  84. Scabiosa (pincushion flower)
  85. Sedum (stonecrop)
  86. Sempervivum (houseleek)
  87. Sidalcea (prairie mallow)
  88. Staphylea* (bladdernut)
  89. Stokesia (Stokes’ aster)
  90. Syringa (lilac)
  91. Thalictrum (meadow-rue)
  92. Tiarella (foamflower)
  93. Tricyrtis (toad-lily)
  94. Trillium* (trillium)
  95. Trollius (globeflower)
  96. Tsuga (hemlock)
  97. Vernonia (ironweed)
  98. Veronica (speedwell)
  99. Viola (violets)
  100. Vitis (grape, some species)
*Some species in this genus require a double cold stratification: that is, two cold treatments separated by warm one, to germinate well. Try two to three months of cold followed by two months of warmth, then again two to three months of cold. When you expose them to warmth after these repeated treatments, most will germinate quite readily.

Good growing!20180103 ENG worldartsme.com, rdkate.blogspot.ca & mzayat.com.jpg