Winter Gardening – This is the talk I gave to the Wanaka Garden Circle a couple of weeks ago - a bit long but some useful info in there if you live as we do somewhere that has a definite winter.
Soil:

Soil moisture is a major factor in plant hardiness. Plants suffer more when their roots are in water logged soil. Wet soils are colder than drier soils and the roots freeze in the ground. Many plants can cope with severe cold if planted in well drained soils. Plants will generally succumb in clay soils that have high moisture content with these heavier soils being slower to warm in spring.

Understanding how plant growth is affected by frosty winter soil emphasises the importance of preparing the soil before planting. Applying mulch to the gardens will act as a blanket. Refrain from clearing the garden beds from fallen leaves during Autumn, it’s natures mulch which will protect plants and nourish the soil.

Freeze- thaw damage occurs when frozen cells defrost quickly in the morning sun. However, when temperatures start dropping, plant metabolism slows down, slowing growth down. As the plant reduces moisture content and stores sugars to provide growth for the next season, the sugar concentration increases. This forms a natural anti-freeze within the cells.
When planting in deep winter the frost will squeeze the plants & lift them out of the soil where they will dry out if exposed, so care needs to be taken to heel plants in periodically. If the ground is frozen for extended periods evergreen plants can dry out as there is no water available for their roots.
Cold wind:

We welcome light winds to keep the frost from settling but cold wind can be very harmful. If possible, shift pots to a sheltered spot out of the wind.

Remember healthy plants cope better with what winter throws at them. Healthy plants are also more disease resistant therefore it’s worth the effort to give your garden the care it requires. Do not however be tempted to bring out the fertilizer for a winter boost. Unlike us humans who take copious amounts of Echinacaea or Vitamin C in winter, count your plants out. Keep fertiliser well away until soil temperatures start to rise. Fertilizer will encourage new growth which will get zapped by the first sign of frost.
Use evergreens, multistemmed specimens and ornamental grasses to create a strong winter skeleton.
My favorite evergreens are Pittosporum and Holly (Ilex 'JC Van Toll' is a great choice for a small garden as it is self fertile) but there are a long list of evergreens to choose from. Use these to create a clean, green backdrop against which the other plants can sing out.

Choose plants with interesting bark or stem colours so that their true beauty is revealed in fall as the plants lose their leaves. Trees & shrubs with great winter bark that you might like to try include:
• Acer griseum, with its flaky peeling bark
• Prunus serrula, with its almost varnished stem
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For maximum impact, consider planting in groups or as a multistem specimen.
A family of shrubs that must be considered is the red and orange stems of dogwood. Cornus alba 'Siberica' or Cornus Spaethii are two of my favourites and look great planted with Bergenia and Ophiopogon planiscapus 'Nigrescens'. .

Add plants with winter flowers such as the pretty Prunus autumnalis. This winter flowering cherry is less blousy than its springtime counterparts but it is long flowering and works well as a cut flower if you cut a branch and bring it indoors. I love the delicate elegance of winter flowering plants - they brighten up the dark wintery day. Winter flowering viburnums Bodnantense for example has lovely pink flowers in late winter & spring.
Camellias Plant out of cold winds in a rich moist but well drained soil. Do not allow to dry out. Siting under deciduous trees is ideal. Planting away from early morning sun will reduce frost damage to flowers.
Hellebores Plant in a good garden soil and water in dry weather. Remove old leaves from H. x hybrids in early to mid-winter.
Hamamelis Prefer rich moist but well drained soils that are acidic rather than alkaline. Full sun to part shade and protection from strong winds.
Chimonanthus Most soils, prune only to tidy and immediately after flowering or you will lose next years blooms.
Daphne Rich, humusy soil, well drained and does not dry out. Avoid sodden soils. Protect from drying winds.
Snowdrops Prefer a soil rich in humus, moist but not wet. Divide and replant in 'the green' after the flowers have faded
Viburnum Good, moist but well drained soil.
Cornus Good, moist but well drained soil. Prune out 1/3rd of the oldest stems each year or so to encourage new growth as this gives the best colour.
Mahonia Most soils, very hardy.
Garrya elliptica Most soils. Withstands wind but better display with some protection.
Euphorbia Any soil, prefers full sun and good drainage. Cut back dead flowering stems with care - the sap is toxic and can cause a rash.
Nandina domestica Plant in good soil in partly shades position. Moderately frost hardy - more so in well drained soils. Prune old, tatty wood to the ground in spring. Growth becomes limp, discoloured and disfigured.