Give your plants a hand by picking the perfect spot

Most gardeners relish a challenge. It may be that they like to harvest the earliest new potatoes on their allotments, pick raspberries out of season as late as November or force succulent bunch carrots in a cold frame. But this challenge is not limited to edibles.

Exploitation of an especially warm, dry or cool area to grow something special there is what gardening in micro-climates is all about.

Now this may be something as simple as allowing (just try to stop them) Mexican Fleabane or the yellow-flowered Corydalis seed themselves into every crack in your paving. This creates a lovely cottage garden effect but in the case of the Mexican plant the radiated heat from the paving will help this plant get through our winters.

Cool north-facing walls tend to remain damp and this suits most ferns, but for more colour the harebell Campanula portenschlagiana is a real winner and relishes the conditions there.

Dry stone walls offer all sorts of opportunities with pretty multicoloured Lewisia benefiting from the dry micro-climate there. Lewisia and many other alpine plants hate to have water on their leaves. The exception is in spring when the snow covering that keeps them dry all winter quickly melts and disappears.

At the base of the wall and on the sunny side, agapanthus and late flowering bulb Nerine will enjoy the dryness and reflected heat, and perhaps "think" they are back home in South Africa.

Some of the most reliable flowering agapanthus in my garden chose their spot by seeding into the edge of a path close to the house where it stays warm in winter and, because it has to fight for survival in such a small root space, blooms with profusion every year.

To grow anything under a dark dense conifer is perhaps the greatest challenge but Butchers Broom (Ruscus aculeatus) is sometimes found there in our native woods.

Here the soil must be poor and rock hard all of the year but somehow this plant finds those conditions to its liking. There are few other plants that will grow under yew trees but the evergreen Viburnum davidii (plant both male and female plants to get those stunning blue berries) will often succeed along with variegated Persian ivy as ground cover.

House leeks (Sempervivium) will grow on the roof tiles with a little bit of help to get them started. Once going, they gather enough water when it rains to see them through dry periods and enough food from the detritus that is in the air.

Rather than drain damp and boggy soils, Royal ferns and so-called marginal plants such as Astilbe, Arum lily, Ligularia, loosestrife and many others will relish such conditions and produce colour throughout the summer months with the minimum of attention.

Of course, walls present some of the best micro-climate opportunities as the old walled garden testifies. Tender plants growing against south or west-facing walls receive the best protection from winter cold and it is surprising just what can be grown outside if you really try. After all, succulents and even cacti from the Mexican and South American deserts are flourishing in a dry sheltered man-made crevice at the Cotswold Water Park.

Alan's Plant of the Week

Periwinkles – what a charming name.

Sometimes found carpeting deciduous woodland as a very pretty native plant, periwinkles (Vinca) are tough and very easy to please plants.

But not all have good manners in the garden and while the smaller leaf and lower growing Vinca minor varieties are suitable, I would think twice about planting a larger leaf and much more vigorous Vinca major variety in any but the largest garden.

Now Vinca minor is a great low-maintenance carpet former that can effectively smother all but the most persistent weeds. It grows well in shade or in sun and one of its greatest attributes is that it will form new roots where shoots touch the ground so that a dense and neat carpet is quickly formed. This is a perfect plant to cover the ground below shrubs and trees, and will quite quickly coat steep banks that would otherwise be difficult to mow if sown to grass.

Some varieties, such as the boldly gold variegated Illumination, look good trailing over the edge of containers or growing in winter planted hanging baskets, and the blue star-shaped flowers that appear at this time of the year are the perfect contrast to the trailing variegated leaves.

Not all periwinkles have blue flowers and Vinca minor Gertrude Jekyll is one to seek out, either to plant on its own or to combine with the best blue called Bowles Variety. However, purple flowered atropurpurea is not to be shunned, but I'm afraid that I can't get excited about double-flowered varieties.

In my view, one of the very best all-rounders is the silver variegated but soft-blue-flowered Ralph Shugart and this is a fitting tribute to a late American nurseryman who had an excellent eye for exceptional plants.

Alan's gardening tips for the weekend

Start spraying roses for blackspot, rust and aphids with Roseclear Ultra as soon as the leaves appear. Early spraying is essential.

Prune side shoots on winter flowering Jasmine back hard. Japonicas (Chaenomeles) can be cut back when they finish flowering too. This gives time for next year's buds to form.

Check trellis support for climbers and reinforce or replace before growth begins.

Divide overcrowded clumps of herbaceous perennials, discarding the older central part and replanting the younger more vigorous outer sections.

Make a concerted effort to get on top of weeds now, they are about to make a serious spurt of growth. Remove by hand or spray with the new weed killer Resolva.

Top dress alpine plants with horticultural grit to ensure that there is fast drainage around the base of the plant.

Prune blueberry bushes by removing weak, old and dead shoots. Cut out up to 25 per cent of all wood from established bushes (three years or older).

Plant strawberry runners if you missed autumn planting.

Regularly remove yellowing leaves from brassicas. These may be suffering from downy mildew and can carry this disease over to reinfect new crops.

Divide and replant overcrowded clumps of herbs.

Sow parsley, chervil, chives and fennel. Coriander can be sown under cover.

Open the greenhouse ventilators on warm days.

Remove the bubble polythene from greenhouses and make sure that the glass is as clean as possible.

Top-dress lawn hollows with turf dressing

Roll lawns (slowly) to even out bumps. This is especially effective when the soil is moist.

Reshape lawn edges using a sharp half-moon lawn edging iron. Consider installing lawn edging to support the edges.

Ask Alan