Althea

Light and exposure

Althea wants as much sun as possible. A spot that catches the midday and afternoon sun, 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 a climate with cool, windy summers, a place against a sunny wall or in a sheltered corner of the garden makes a real difference to how many flowers you get: the wall stores the day’s heat and gives it back after sunset, and it is that summer heat that drives the flowering. Avoid low spots where cold air pools at the end of winter, 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, right through the flowering season, keeps the display 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 thoroughly hardy in the open ground, from USDA zone 5 to zone 9: it copes without damage with cold down to minus fifteen to minus twenty degrees once well established. It is a shrub built for cold winters, unlike its indoor cousin, which cannot take any frost at all. For the first two winters, while the roots are still shallow, a good mulch at the base settles the question.

What surprises people most is how slow it is to start. Even after a mild winter, it keeps its branches bare for weeks after every other shrub in the garden. That is not a sign of poor health, it is simply its nature, and it is exactly what puts it out of reach of late frosts, so 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, 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 the middle of summer, 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 still bare when the whole garden has already greened up, it is the last shrub to leaf out, it always gets there in the end.
• Prune in late winter, 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, which runs from midsummer to the first frosts, when the rest of the garden is already done.