Plant therapy needed after the heat and wind

Judith Adam

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Rudbeckia nitida 'Herbstonne' (Photo by Brendan Zwelling)
Rudbeckia nitida 'Herbstonne' (Photo by Brendan Zwelling)
Rudbeckia nitida ‘Herbstonne’ (Photo by Brendan Zwelling)

The past summer’s intense high heat and forceful winds were challenging for plant health, causing leaf tissues to desiccate and raising soil temperature in the root zone (the top 6 to 12 inches/15 to 30 cm of soil). I’m just glad to have it over and move into a cool autumn season, but plants are more permanently affected. If they enter winter dormancy in a debilitated condition, we can expect to see twig dieback on woody plants and reduced size of perennial plant clumps next spring.

In fact, I’m already noticing signs of plant stress. Leaves on many trees (birches, in particular), and rose of Sharon (Hibiscus syriacus, Zone 6) appear drab and are losing their green chlorophyll. My guess is that some leaves will fall prematurely this autumn, perhaps two or three weeks earlier than normal. And I also notice some of my perennials, like ‘Jack Frost’ Siberian bugloss (Brunnera macrophylla ‘Jack Frost’, Zone 4) and Rudbeckia laciniata ‘Herbstsonne’ (syn. R. laciniata ‘Autumn Sun’, Zone 5), are smaller than other years. I think the roots of these plants are damaged, having been cooked in overheated soil.

Plant therapy

Restorative therapy for plants this autumn could make a much happier spring for gardeners. Fortunately, we’re having some days and nights of healing rain in Ontario, the kind that falls consistently for hours and allows moisture to percolate down to the root zone. This is the best therapy for plants, and also for the biological life of soil. The many different soil organisms that process organic materials into mineralized nutrients rely on consistent moisture as a foundation for their work.

I’m inclined to do a bit more to encourage plant roots to grow in the four to six weeks remaining before the ground is frozen. Cooling soil temperature generally inhibits root growth, but a little rooting hormone might overcome that hesitation, and produce root repair this autumn. I’ll give herbaceous perennials (and some woody shrubs) a drink of liquid transplant solution, which contains a low dose of fertilizer (5-15-5) and rooting hormone (I.B.A., or indole-3-butyric acid). I use it when dividing perennials in fall and re-settling the divisions in their holes, as well as in spring when installing new plants. It’s extra therapy I can provide for stressed-out plants that have been compromised by too much heat, and a bit of insurance against unnecessary winter dieback. That’s smart gardening.

Darwin tulips, again and again

If you like large-flowered tulips that are strong repeat bloomers, Darwins are your best bet. Tulip breeding goes back centuries and traits like size and repeat performance are the result of mixed genetics. Modern Darwin tulips have benefited from an infusion of genes from Fosteriana tulips (known for their ability to repeat and naturalize). Inherited red Darwin tulips have been blooming in my garden for more than 20 years! I’ve even tried digging them up, but there are still bulblets left behind that mature to produce flowers (those Fosteriana genes). Some bulb authorities say the older Darwins (mostly red and yellow) have the greatest longevity.

Darwin tulips are hardy to Zone 3 and bloom in May. They were originally dominated by colours such as blazing red (‘Appledoorn’) and yellow (‘Golden Parade’), but modern hybrids include pinks—from lightest apricot-pink ‘Apricot Delight’ to rosy ‘Pink Impression’—and milky white ‘Haakun’. My current favourite Darwin is ‘Daydream’, which starts out creamy butter yellow, gradually turning to apricot-orange, like two tulips in one. There are dozens of solid, striped and bi-colours available, so make yourself happy!

Plant Darwin tulips eight inches (20 cm) deep in a sunny location in soil that drains well. Be sure the soil is moist at planting time, and again in spring when the bulb tips show above ground. When the flowers are finished, break off the central seedpod so that all energy will be directed into the bulb, and allow the leaves to continue growing. Use a granular perennial plant fertilizer around the leaves to provide additional energy for making large flowers next year, and water the bulbs regularly. Expect the foliage to hang on for about six weeks, and cut leaves off at ground level when they are half brown. At that point, they’ve died back enough so that their ability to manufacture more energy is negligible. The bulbs won’t require additional irrigation in the summer.

Russian sage, begonias and salvia going strong

Russian sage (Photo by Brendan Zwelling)
Russian sage (Photo by Brendan Zwelling)

Still blooming and looking terrific in the garden are Russian sage (Perovskia atriplicifolia, Zone 4), and two summer annuals—fibrous root wax begonias and dark blue salvia ‘Victoria’. These last two may be ordinary gas station plants (that is, often seen in service station flowerbeds), but you can’t argue with success.

Shedding conifer needles

October is the month when evergreens drop about one-third of their foliage, called conifer cast. It’s part of their annual renewal cycle; each spring they replace the cast needles with new growth. You’ll notice the lovely mulch these fallen needles make all around the base of conifers. Where it’s generous, I’ll use some to mulch Cyclamen hederifolium corms (Zone 5) and the tubers of double bloodroot (Sanguinaria canadensis f. multiplex ‘Plena’, Zone 5), both of which lay perilously close to the soil surface. And no need to worry that conifer needles are excessively acidic, because they aren’t. In fact, they hardly affect soil acidity or alkalinity at all, but they are a wonderful mulch and soil amendment, improving drainage and bringing oxygen to the root zone.

Hope to see you back at Garden Making next week. Until then, cheerio!

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4 thoughts on “Plant therapy needed after the heat and wind”

  1. To Don McLean, Oct. 8

    Thanks, Don. Liquid transplant solution can be used on all kinds of plants, including food plants. Just follow the instructions on the container.

  2. To Alex, Oct. 7

    Hello Alex,

    You've been successful with your chocolate vine—perhaps too successful! Akebia quinata (zone 5) is an aggressive twining vine and rampant groundcover, with scented rosy purple flowers and attractive foliage on tendrils that travel in vertical and horizontal directions. There's nothing that will outright kill it, but you can begin work on eliminating it by digging out the original root ball planted 9 years ago. Then work on digging out roots where the vine has touched soil as it travelled. If you make a concerted effort at digging it out this autumn, and again next spring, you may get ahead of it. But I expect you'll be finding it around your landscape for some years to come. The general warming of our climate encourages the growth of aggressive plants, and we may all be struggling to control our vines! Good luck.

  3. This is an unrelated question I hope you can help with…I bought a chocolate vine 9 yrs ago and it has turned out to be extremely invasive sending 60ft runners anywhere it can. How can I kill it?


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