Weather: The winter of 2004/05 was generally mild, but with more mornings with snow lying than has been seen in recent years. Following on from a wet late summer and autumn the ground remained wet throughout, exacerbated by a wet spell in early January. (National records have this winter relatively dry, which is not my subjective impression.) November and December were mild, with occasional frost, and a colder spell with 4 mornings with snow lying at the end of December. January was similar with a colder spell at the end of the month, with 2 mornings with snow lying. A period of northerly winds gave a colder spell in late February and early March, with frequent frosts.
Plants were grown in 2 locations perhaps 400 yards apart, and in the ground and in pots. Survival differed significantly between these locations, and contrary to conventional experience, pot grown plants survived better, suggesting that waterlogging was a worse problem than frost. Microclimate would also seem to be important.
Annuals and Biennials: Annuals - Anoda cristata, Hibiscus trionum, Lavatera trimestris and Malope trifida - were removed without observing how late into the winter they would survive, as was Malva sylvestris 'Zebrina'.
Some plants of Malva linnaei (Lavatera cretica) and one plant of Malva verticillata overwintered. All plants of Malva australiana (Lavatera plebeia) and Malva durieui (Lavatera mauritanica) were killed, including self-sown autumn germinated seedlings.
Most ground-grown plants (1 exception) of Malva sylvestris that had flowered the previous summer died overwinter, even though in some cases the parent plant is perennial. However, they had suffered badly from hollyhock rust, which may have weakened them. Several pot-grown seedlings, cuttings, and plants also died, but some survived.
Herbaceous Perennials: Some specimens of Alcea rosea survived; others did not. Many seedlings of various forms of Alcea were lost.
The resting buds of Althaea officinalis and Althaea officinalis 'Alba' were scorched by frost, but the plants produced additional shoots from the rootstock.
Plants of Kitaibelia vitifolia came through the winter undamaged.
Most speciemens of Malva moschata come through the winter without ill-effect, but some of the older and less vigorous specimens were lost. All specimens of Malva alcea, Sidalcea ×hybrida and Sidalcea cf candida come through without ill-effect.
One group of Lavatera thuringiaca, were lost, perhaps due more wet conditions and slug and snail grazing than to frost, as were the weakest 3 seedlings of the last year's sowing. Other specimens of Lavatera thuringiaca lost some shoots; this may have been slug or snail damage. Pot grown specimens of Lavatera 'Summer Kisses', Lavatera 'Sweet Dreams' and Lavatera 'White Angel' overwintered without ill-effect.
Supposedly perennial specimens of Malva sylvestris ('Marina' and a sterile blue-flowered plant of 'Mystic Merlin') were lost. A specimen of "Malva" 'Park Allee' survived, losing all top-growth, thus behaving as a herbaceous perennial, rather than the sub-shrub it was labelled as.
Subshrubs: All specimens of Anisodontea capensis grown in the ground were lost. A pot grown specimen passed the winter without ill-effect.
The top growth of Lavatera ×clementii 'Candy Floss' was progressively lost, necessitating treating this as a herbaceous perennial (the basal shoots produced in the autumn were unaffected), except that a few side shoots remained, which were used as cutting material in April. A specimen of Lavatera ×clementii 'Burgundy Wine' was severely cut back - only a single shoot remaining - but this was probably due to waterlogging, having occured by November. A weak specimen of Lavatera ×clementii 'Memories' was finally lost. Lavatera ×clementii 'Lisanne' was unaffected by the winter.
A border grown specimen of Sphaeralcea ×hybrida 'Los Brisas' failed to survive; a pot grown specimen did survive. Pot-grown specimens Sphaeralcea 'Hopley's Lavender' and Sphaeralcea 'Newlease Coral' overwintered with some loss of top-growth, but with some protection for the worse of the February cold spell.
Shrubs: Pot grown specimens of Abutilon ×hybridum all lost their foliage progressively over the winter, but all survived without major damage. This was not the case for speciments grown in the ground; 3 specimens (of 2 clones) have definitely been lost, and the remainder don't look happy, and have no leaves as yet. Of those lost, the lethality may have been due to wet, or ring-barking by slugs or snails, rather than to cold. A specimen of Abutilon megapotamicum appeared dead by November, but new shoots finally appeared by mid-April.
A seedling of Corynabutilon was sucessfully overwintered outdoors in a pot.
Fremontodendron 'California Glory' was unaffected by the winter conditions.
Assorted cultivars of Hibiscus syriacus came through the winter without ill-effect.
A border grown specimen of Lavatera 'Bicolor' died during the March cold spell, having previously lost some shoots during earlier cold spells. A pot grown specimen was unaffected.
Cultivars of Lavatera ×clementii and Lavatera olbia generally came through the winter unscathed. Most of the top growth of ground-grown specimens of Lavatera ×clementii 'Barnsley' was lost.
© 2005 Stewart R. Hinsley