Althea

Light and exposure

Althea wants as much sun as possible. A south or south-west facing spot, sheltered from cold, drying winds, gives the most generous flowering. In part shade it still grows and flowers, but less abundantly and with a shape that tends to stretch towards the light.

In the Herve region, where summers can stay cool and windy, a spot against a wall or in a sheltered corner of the garden makes a real difference to how many flowers you get. Avoid low spots where cold air pools in spring, since that only delays a leafing out that is already late.

Watering

Once well rooted, after two or three years in the ground, althea copes well with dry spells and needs no special watering. Young plants, on the other hand, need regular watering in the first and second year, while the roots settle in deep.

The point to watch is flowering. A summer that is too dry, with no watering at all, often makes the flower buds drop before they even open. A generous watering once a week during prolonged dry spells, from July to September, keeps the flowering going.

Soil and repotting

Althea is not fussy and is happy in ordinary garden soil, as long as it drains well. A little compost at planting helps young plants get off to a good start, but no further feeding is really needed after that.

The real weak point is too much water in winter. In heavy clay soil that stays waterlogged for weeks, the roots eventually rot. In poor, chalky soil, chlorosis can appear, with leaves turning yellow between veins that stay green, a dose of compost or iron usually fixes it.

Temperature and humidity

Althea is perfectly hardy here, coping without any damage with cold down to minus fifteen to minus twenty degrees once well established. It is a shrub built for our winters, unlike its indoor cousin, which cannot take any frost at all.

What often surprises gardeners in the region is how slow it is to start in spring. Even in a mild year, it keeps its branches bare long after every other shrub in the garden, sometimes right into May. That is not a sign of poor health, it is simply its nature, and you have to resist the urge to dig it out too soon.

Pruning and upkeep

Althea flowers on the current year’s wood, meaning on the shoots that grow during spring and summer. Pruning in late winter, in February or March, before the leaves come out, encourages vigorous regrowth and more, larger flowers in the growing season.

Cut back last year’s shoots by a third to half their length, just above a bud. This pruning is not compulsory, an unpruned althea still flowers, but it genuinely changes how generous the summer flowering is.

Pests and diseases

Althea is a generally healthy shrub that rarely causes real problems. Black aphids are the most common issue, settling in colonies on young shoots and flower buds in spring and early summer. A firm jet of water or some soft soap usually gets rid of them.

On poor, chalky soil, watch for chlorosis, yellow leaves with green veins. And if flower buds drop without opening in high summer, that is not a disease but a sign of too little water, corrected by watering more generously during dry spells.

Propagation

Taking cuttings is the most reliable way to get an althea identical to the parent plant. Take semi-ripe cuttings in July or August, from this year’s shoots that have already firmed up a little at the base, and root them in a light mix, in the shade.

Growing from seed is possible but really for the curious, since flowering only starts after several years and the flowers you get do not always match the parent plant, as garden varieties are often hybrids. Layering, bending a low branch down into the soil until it roots, also works well.

Month-by-month care calendar

Green Hub tips

• Never worry about seeing althea bare in April or early May, it is the last shrub in the garden to leaf out, it always gets there in the end.
• Prune in February or March, before it leafs out, althea flowers on the current year’s wood and regular pruning gives more and bigger flowers.
• Water generously during dry summers, especially at the height of flowering, otherwise the buds drop before they even open.
• Plant it in full sun and sheltered from the wind to make the most of its late flowering, from July to October, when the rest of the garden is already done.