Mallow Care: Keeping It Upright, Unfed and Free of Rust

Feeding is what makes it flop

The commonest mallow complaint is a plant that splits open at the base in midsummer and lies flat across its neighbors. This is almost never a staking problem. It is nitrogen. Fed mallow makes long, soft internodes and huge leaves, and the crown cannot carry the weight once the stems are wet from a night of rain.

Give it nothing. Mallow grown in ordinary garden soil with no feed at all makes shorter internodes, thicker stems and more flowers per foot of stem than the same plant given a general fertilizer. If the ground is genuinely exhausted, a single low-nitrogen feed as the flower buds form is the most it needs, and even that is optional.

If a plant has already gone soft, do not try to prop the whole thing. Cut the worst stems back by half to a strong side shoot. The plant rebuilds on shorter, stiffer growth within three weeks and flowers again on it.

If you must stake, do it in early summer with a ring or a grow-through support the plant grows up into. Tying a collapsed plant to a cane in midsummer strangles the stems and leaves the middle of the clump as a still, damp pocket.

Pinch once, early, and get a wider plant

Left alone, mallow tends to make one dominant stem with side shoots strung along it. A single pinch when the plant is eight to ten inches (20 to 25 cm) tall breaks that dominance and produces four or five stems of roughly equal strength from low on the plant.

The result is a shorter, wider, sturdier plant that carries more flowers and is far easier to pick from, because the flowering stems are at chest height rather than over your head.

1. Pinch the growing tip at eight to ten inches Take out the top inch (2.5 cm) of the leading shoot with your fingernails, cutting just above a leaf joint. Do it before any flower bud is visible; pinching later costs you three weeks of flowering.
2. Leave the side shoots alone Do not pinch the resulting side shoots as well. A second pinch delays flowering badly and produces a congested, twiggy plant that holds damp air in the middle.
3. Skip the pinch on late sowings A plant sown after early summer has no time to spare. Let it run straight up to flower rather than spending three weeks rebuilding a branched frame.

Water the ground, not the leaves

An established mallow with its taproot down rarely needs watering at all. It wilts in the afternoon heat and recovers by evening, and that afternoon wilt is not a signal to water. Push a finger four inches (10 cm) into the soil instead: if it is damp at that depth, the plant is fine.

When you do water, deliver it at the base of the plant, slowly, and enough to soak down. A gallon (4 liters) poured at the crown once a week in a drought does more than a daily sprinkle. Overhead watering wets the leaves, and wet mallow foliage is how hollyhock rust gets established and spreads.

1. Water in the morning if you water at all Any splash on the lower leaves needs to dry within a couple of hours. Evening watering leaves the base of the plant damp all night, which is precisely the condition rust spores need to germinate.
2. Mulch instead of watering more An inch (2.5 cm) of coarse mulch kept clear of the stem itself holds moisture and, more usefully, stops soil splashing spores from old debris up onto the lowest leaves.
3. Containers are the exception A potted mallow has no taproot escape route and will need watering most days in hot weather. Water until it runs from the bottom, then let the top inch dry before the next one.

Strip the lower leaves and keep the base open

The oldest leaves at the bottom of the plant are the first to catch rust, the slowest to dry after rain, and contribute almost nothing to the plant by midsummer. Taking them off is the highest-value ten minutes you will spend on a mallow all year.

Remove the bottom six to eight inches (15 to 20 cm) of foliage once the plant is knee high, and keep that zone clear all season. Anything you remove goes in the bin, not the compost pile, because rust spores survive composting at garden temperatures.

Never compost mallow foliage that shows orange pustules, and do not leave stripped leaves lying on the soil under the plant. Both routes bring the disease straight back next season.

Cutting back for a second flush

Mallow flowers in a long first flush and then starts putting energy into seed. Once roughly three quarters of the flowers on a stem have gone over, cut that stem back by a third to a half, to just above a healthy pair of leaves. New shoots break within two weeks and carry a lighter second flush that runs to frost.

Do this stem by stem over a week or two rather than shearing the whole plant at once. Shearing takes every flower off in one go and leaves you with a bare plant for a fortnight; staggering it keeps something in flower throughout.

1. Cut above a leaf joint, not into bare wood Find a pair of healthy leaves low on the stem and cut a quarter inch (6 mm) above them. A stem cut into a bare section between joints often dies back to the next joint down anyway.
2. Take out the worst stem entirely There is usually one stem that is rustier or floppier than the rest. Cut it to the ground rather than shortening it. Removing it opens the middle of the plant and costs almost no flower.
3. Do not feed after cutting back The instinct is to feed the plant to help it recover. Resist it. The regrowth will be soft and rust-prone, and the plant regrows perfectly well on what is already in the soil.

The care notes worth keeping

Mallow behaves consistently on the same ground year after year, so the notes you take this season are directly usable next season rather than being general advice.

Record the dates of the interventions and what the plant did afterwards, not just the fact that you did them. The gap between a cut back and the first new flower is the most useful single figure you will collect.