22 February 2016

Page topic: Plants to Beware Of

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Changes in purple       21st November 2015

Plants to beware of:

Ann N         13 March 2015

“A friend of mine has a Monkshood plant in an overgrown border which has very compacted soil. As she has young grandchildren she wants to get rid of it. She is unable to dig it out.

Has anyone any suggestions as to how she could tackle this?  Small green shoots are just beginning to appear.”

Sydney replied, “I should expect that glyphosate (Round-Up) would be effective, though if the enemy is long established it might require a second treatment. The bonus of this herbicide is that it is harmless to people and pets.”  There are applicators you can buy that apply Round-up leaf by leaf, as I hope the friend’s Monkshood has now discovered.

Certainly, children or none, I would not choose to grow Monkshood or any other Aconitum - nearly all have deadly poison in the sap: poisoning can occur from the leaves through ungloved hands. Besides, they are rather gloomy flowers.

Sydney, 21 February 2015, including material from Kay and with later additions on 15-05-2015

I thought members might like to contribute warnings against plants that people living in our area should not buy: either because they don't earn their keep or they make a lot of trouble if neglected. Apart from Kay’s Euphorbia problem, nobody told on any plants while my list was in the members’ web-log, but here's my list, now fortified:

Invasive by seed: Leycesteria formosa; Alchemilla mollis; Paeonia lutea (though easy to control).

Too tender for outdoors: Convolvulus cneorum; Rhododendron (azalea) 'General Wavell'; R. (azalea) x mucronatum 'Noordtianum'; Viburnum tinus 'Eve Price'; almost all Cistus.

Short-lived: Broom; most Daphne; Halimiocistus; Laburnum; most Lilies; Rosa xanthina and most non-shrub roses !

Feeble flowerers: Hebe 'Mrs Winder'; Prunus x subhirtella 'Autumnalis'; Viburnum farreri (ex V. fragrans 'Bodnantense'), (PS farreri was good in January 2013, but did it really deserve the space?).

Invasive below ground: most bamboos; Gaultheria shallon; Phygelius x rector Moonraker et al; Romneya coulteri (but worth it).

Dirty flower colour: most Olearia, Rhododendron (azalea) 'Blue Danube', R. niveum, Viiburnum rhytidophyllum,

Prone to disease: most low-growing Juniperus, Camellias now that petal blight is on its way here.

Too prickly (a new category): Poncirus

Too floppy (a new category): Helleborus corsicus; fully double lactiflora Paeonies like ‘Sarah Bernhardt’, unless under covers.

To reinforce the warning about Leycesteria, we have now proved that the seed can lie dormant for twenty years - maybe longer.

There are one or two plants whose bad habits are forgivable though: of Romneya coulteri, the Californian tree poppy, wikipedia says,  “Eight feet tall and if in a light soil forever wide”. It spreads by deep rhizomes, but takes a few years to develop its ambition in our medium loam, taking advantage of the easy root run along the footings of the house walls.  Excavation, supplemented by judicious application of glyphosate, has controlled this poppy so far.


The finest shrubs for even slightly acid soils include evergreen Rhododendron and Camellia, but if there are any scale insects in your neighbourhood you must do without almost all these.  The exceptions are the few Rhododendron that have lovely furry leaf undersides, which seem to prevent the scales from attaching to the leaf.

Kay had a problem with an un-named Euphorbia that was very invasive: my mother had, too. Since I have never seen a(n) Euphorbia I liked, I have been free of that particular trouble.  There’s one kind of invasiveness that I positively enjoy seeing, though: the gentle climbers. The viticella and texensis classes of Clematis are good examples: for us at least they never smother their hosts, but always enhance them, and to me they never look happy on artificial supports without the company of more robust genera. Val and I couldn’t agree about the Heavenly Blue low-growing Lithodora diffusa, which gradually climbed up and up into a trio of apricot Potentillas, still allowing them enough light to show their flowers above the lithodora foliage. I thought it gentle enough

Helen Dillon confessed to scrapping Sisyrinchium ‘Aunt May’  because it clogged up with black dead leaves, and a Lady’s Slipper orchid because it couldn’t stand up.  She found May Queen, the oriental poppy, too invasive to remain.  She introduces an additional category, Ugly Variegation, to which she assigns a Fritllaria, ‘Argentovariegata’, the variegated version of Abutilon megapotamicum, and the blackberry ‘Variegatus’.  I would add every variegated plant that is inconsistent in its patterning,  but most gardeners might consider that intolerant, even bigoted!

If any of you can remember the reasons Maurice Parkinson gave us for warning against Escallonias, Forsythias, or Hebes, please let me know them!

members #hs_168