Rio portulaca for hot spots

Rio Yellow Purslane at Variety Trial in 2012 at Missouri State University.

Rio Yellow portulaca at plant trials in 2012 at Missouri State University.

I’ve been gardening for 30 years, but it’s still a new day when I trip over a problem and discover growing insights. First, the happy solution. A beautiful pot of annual Rio Series yellow portulaca (Portulaca oleracea) has been the key to understanding unexpected problems on my front walk gallery of ornamental plants and tomatoes in containers. It’s been a few years since I last looked at portulacas, and my goodness, what changes the hybridizers have wrought in these pretty, serviceable plants.

Older versions of portulaca looked a bit hairy, crawly and primitive, as would be expected from a plant not far evolved from its purslane origins. A South American breeding program in Cartago, Costa Rica, took genes of species portulaca (P. oleracea, P. umbraticola and P. grandiflora) and produced the Rio Series (8 x 16 inches / 20 x 40 cm), a noticeably improved generation of colourful plants with stouter stems, an arching posture and svelte, succulent foliage. The large ruffled flowers (yellow, white, scarlet or orange, all with yellow centres) close at night, but stay open under overcast skies, unlike older portulacas that close on cloudy days.

Now, for the distressing problem. Last year’s removal of a large fern-leaf beech tree (sadly missed, but it was too big) in the front garden created a very bright planting space. Some areas have become too hot for certain plants, such as ‘Sum and Substance’ hosta, while a few, like perennial salvias, penstemons and Russian sage (Perovskia atriplicifolia), have shown enthusiasm for the increased light. I’ve been moving new plants into these hot spots, looking for potential sunbathers that could form a new and permanent collection.

The brightest area is along the front pathway, where I put containers of tomatoes, knowing they would excel in the heat and sun. (Please restrain your laughter and pity the misinformed gardener.) I had forgotten a sharp lesson learned last year, when tomatoes in that location developed strange white blotches on their foliage and their growing tips stopped expanding. When they were moved to less intense light, the blotches disappeared and growth resumed. This year, the tomatoes had brown colouration creeping inward from the leaf edges, and some had markedly stunted growth. Both years, the changes in leaf colouration and retarded plant growth occurred quite rapidly.

The brown-leaved tomatoes were swiftly pulled back to parts of the path with less intense light, and I retreated to the computer for some Internet research. The American Horticultural Society’s heat zone map is a most illuminating resource (pun intended!) with information about how plants use light during climate change (see ahs.org/gardening-resources/gardening-maps/heat-zone-map).

Nowadays, we have more intense heat and sunlight than when my grandfather was growing tomatoes, and this directly affects how much is absorbed by plants, and what they do with these resources. And not all the effects are good. Full-spectrum light can enter plant foliage, but only rays with shorter wavelengths can exit. Longer-length light rays are trapped inside foliage, accumulating heat over successive sunny days with high temperatures.

Heat resistance and tolerance of environmental stress are related to the evolutionary location of a species. Some plants (presumably like tomatoes) begin to suffer physiological damage from heat accumulation at temperatures over 86°F (30°C). Others, like portulaca, can endure greater heat accumulation in their foliage and continue healthy growth. As foliage tissues accumulate heat, biological changes occur, such as the dispersal of chlorophyll and tissue discolouration. I learned that heat-stressed foliage will change from green to white or brown — and doesn’t that sound familiar?

Well, I guess all has been revealed. Tomatoes can’t take so much sun-generated heat, and portulaca doesn’t mind at all. It’s always something.

Comments

  1. Judith Adam says

    Hi Marie,

    Thanks for your information about the portulaca Fairy Tale Series. I haven’t grown it, but did look at some pictures – and wow! What a bombshell flower.

    I found a reference to Fairy Tale Series seeds on the Internet, but no source. You might be interested to read the grower comments on Dave’s Garden site: http://davesgarden.com/guides/pf/go/67558/ . (Scroll down the page for the growing comments.)

    Most often, reference is made to growing this plant from cuttings, and that seems to be easy and successful. The plants apparently make little if any seeds. The reason for this is apparent, as their centres are packed with petaloids resulting in the extreme doubleness that is so attractive in this portulaca.. Petaloids are stamens that have been partially converted to petals, to achieve the double centres. But that process leaves the plant devoid of the sexual organs necessary for seed production. Hence, few or no seeds at all.

    The plants will strike from cuttings quite easily, and that would be the way to go if you want to make more. It would be possible to take cuttings from healthy plants in mid or late summer, and grow them on in a sunny window through winter. If they remain vigorous, the plants could go outside next spring.

    —Judith Adam

  2. Marie says

    I agree with you about the Rio portulacas -they’re really very nice. I’ve bought hanging baskets two years in a row now with a combo of the yellow and pink varieties for an especially hot spot, and they’ve done wonderfully well. The orange toning on the pink flowers complements the yellow in the baskets so well. I especially appreciate that they’re water misers and don’t mind being a little dry, and haven’t needed watering more often than every 2-3 days.

    Searching for more info on them, I came across the ‘Fairy Tale’ portulaca series. The most photographed one is ‘Cinderella’, with absurd double flowers of yellow around a boss of fuchsia pink. Though they’re rather garish, I find them enchanting nonetheless – for the right spot. But where to buy them?? Can’t get seeds because they must be propagated by cuttings. Have you come across them, Judith? Any suggestions of who might carry them?

    I always look forward to reading your columns – thank you!

    Marie

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