The Hibiscus Trio

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Perennial hibiscus (Hibiscus moscheutos) left, Chinese hibiscus (Hibiscus rosa-sinensis) middle, rose of sharon (Hibiscus syriacus) right. Photo: http://www.plant-world-seeds, http://www.amazon.ca & http://www.villagenurseries.com

I receive a lot of gardening questions and a surprising number concern hibiscus. Either a lot of people are growing hibiscuses or a lot of people are having trouble with them! 

The problem is, I can’t answer a question about a hibiscus plant without knowing which hibiscus you’re referring to. So, it would help me (and you) to know which hibiscus you are growing. 

Yet, to many gardeners, a hibiscus is a hibiscus, period. How complicated can it be? 

Very complicated, actually.

Three Out of Hundreds

There are actually hundreds of species of Hibiscus found all over the world, including annuals, perennials, shrubs and—yes!—even trees! Some are grown as ornamentals, others for their edible flowers and fruits and even some for their fibres! All, of course, are in the mallow family (Malvaceae) and their flowers look a lot like mallow blooms, but bigger.

However, when most people refer to hibiscuses, they have one of three species in mind, all, initially, with similar flowers: large and disc-shaped with 5 broad petals and a striking central column composed of anthers surrounding an even longer style. All come in various colors and can be simple, semi-double or double and most have flowers that last but a day, sometimes two, but, of course, all bloom repeatedly.

Let’s look at all three.

Perennial Hibiscus, Hardy Hibiscus, Rose Mallow or Swamp Rose Mallow (H. moscheutos)

Perennial hibiscus (Hibiscus moscheutos ‘Pink Elephant’). Photo: http://www.perennialresource.com

This hibiscus is a herbaceous perennial and is hardy from USDA hardiness zones 5 to 9, even zone 4 with a little winter protection. It can be very tall (up to 15 feet/4.5 m!), but modern cultivars are usually in the 3 to 7-foot range (1 to 2 m). Its stems are quite woody for a perennial and need to be cut back in spring.

Most modern cultivars of perennial hibiscus (Hibiscus moscheutos) have overlapping petals. Photo: amazon.com

Perennial hibiscus starts its growth cycle very late in the spring, often a full month after other perennials have started to sprout, but then grows quickly. It produces huge flower buds that open into giant flowers, often said to be dinner-plate size and that’s scarcely an exaggeration: some are 9 inches (25 cm) in diameter, by far the largest flower of any perennial. They come in a wide range of shades, from white to pink, red and purple, often with a red eye. 

It can be a very late and brief bloomer colder climates, but has long blooming period, from July to September, in milder ones.

The leaves of perennial hibiscus (Hibiscus moscheutos)are quite variable in shape, but usually mid-green. Photo: http://www.monticello.org

Its leaves are quite variable and can be broadly ovate to lanceolate, even heart-shaped, and sometimes bear 3 to 5 shallow lobes. Curiously, the shape can vary on the same plant. They are usually medium green (some cultivars have bronze foliage).

It’s the only one of the three commonly grown from seed.

Rose of Sharon, Shrub Althea and Shrubby Hibiscus (H. syriacus)

Rose of Sharon (Hibiscus syriacus) is a temperate-climate shrub. Photo: amazon.ca

This hibiscus is a shrub adapted to temperate climates: USDA hardiness zones 5 to 8, even 4 with winter protection. It reaches 7–13 feet (2–4 m) in height and branches abundantly. 

Rose of Sharon (Hibiscus syriacus) offers an interesting color range. Photo: spaldingbulb.co.uk

It has the smallest flowers of the three, but still, they are about 1½ to 4 inches (4 to 10 cm) in diameter and very showy. They come in white, pink, red and “blue” (blue-violet), often with a red or purple eye. It also has the smallest leaves of the three, with three distinct lobes.

Chinese Hibiscus, Tropical Hibiscus or China Rose (H. rosa-sinensis)

Chinese hibiscus (Hibiscus rosa-sinensis) is, outdoors, a large tropical shrub. Photo: http://www.kalliergeia.com

Of unknown origin, this plant is a tropical shrub and is only grown outdoors year-round in tropical or subtropical climates (USDA hardiness zones 9 to 11). That said, it is also widely available in temperate climates as a houseplant and patio plant. 

The Chinese hibiscus (Hibiscus rosa-sinensis) comes in a remarkable range of colors. Photo: rsrevathi.blogspot.com

Chinese hibiscus can be anything from 1 to 12 feet in height (30 cm to 4 m) and has woody branches. The flowers, usually about 3 to 8 inches (7.5 to 20 cm) in diameter, come in a wide range of colors: red, pink, white, yellow, peach, orange or purple.

The Chinese hibiscus (Hibiscus rosa-sinensis) is often sold as a houseplant or patio plant. Photo: http://www.lowes.com

It can flower all year long, although generally mostly heavily in spring and summer when grown as a container plant or houseplant. Leaves are dark green (sometimes variegated) and ovate with toothed edges.

Obviously, since it’s a tropical plant, it tolerates no frost.

Synopsis

So, three hibiscuses, all with far too many common names: one a perennial (H. moscheutos), one a temperate shrub (H. syriacus) and one a tropical shrub used as a houseplant or patio plant (H. rosa-sinensis). Give all of them full sun, never let them dry out completely, fertilize occasionally and apply whatever special conditions they need to get them through the winter. But you do need to know which is which if you’re going to succeed with them … or if you want to ask questions about them. 

Only January, Yet Already Time to Sow Seeds?

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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.

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