Japanese Snowball Care: Watering, Feeding and Leaving It Alone

Water deeply, and rarely

This shrub likes soil that stays evenly moist but never sits wet, and the way to deliver that is infrequent deep soaking rather than frequent sprinkling. A light watering wets the top inch of soil, evaporates by the following afternoon, and trains the roots to stay near the surface where they are most vulnerable to the next dry spell.

In the first two seasons after planting, soak the rootball once a week in normal weather and twice a week in real heat, putting on enough water to wet the soil eight inches (20 cm) down. After that, an established plant in reasonable soil needs nothing at all in a normal season and a deep soak every ten days or so through genuine drought.

The reliable signal is the leaves at dawn. Wilting in the afternoon heat is normal and means nothing: the plant is closing down to save water and recovers by evening. Leaves that are still limp first thing in the morning mean the roots are dry, and that is when to water. Push a finger into the soil under the mulch as a check, because the same limp appearance can be caused by roots standing in water.

Feeding: mulch first, fertilizer almost never

Japanese snowball is not a hungry plant, and overfeeding does visible harm. Excess nitrogen produces long soft vertical shoots that break the tiered outline, flower poorly, and are exactly what viburnum beetle prefers to lay eggs on. An annual mulch of compost or well rotted manure over the root area supplies everything the plant needs and improves the soil at the same time.

Leave the shape alone

The main skill in growing this plant well is restraint. The horizontal tiers develop from long unbranched extensions that push out sideways each season, and those extensions look untidy for most of the summer, which is precisely why people cut them. Left alone, they become next spring's flowering layer.

That means no shearing, no rounding off, no shortening the long ones because they stick out. It also means no tidying in autumn or winter. If a branch really is in the way, remove it whole in the window just after flowering rather than trimming it at whatever moment it annoys you.

Two things are worth doing. Cut out dead or broken wood whenever you notice it, at any season, because dead wood carries no flowers and hides pests. And remove any strong vertical shoot that comes up through the middle of the plant, since those grow twice as fast as the tiers and will wreck the layered profile within a couple of seasons if left.

Through the seasons

Spring is the mulch and the beginning of the watch for beetle larvae on the leaf undersides. The weeks after flowering hold the one pruning window. Summer is watering in drought and nothing else. Autumn is the season for planting and for clearing fallen leaves if the plant has had leaf spot, and it is when the lacecap forms carry their fruit.

The plant is fully hardy in most temperate gardens and needs no winter protection once established, though a young plant in an exposed spot benefits from a thicker mulch over the roots in its first winter. Snow load is the real winter risk: heavy wet snow settles on the flat horizontal tiers and can split a branch at the fork. Brush the worst of it off with an upward sweep rather than knocking it down.

Keep a short record each year: the date the flowers opened, the date they finished, the date you pruned, and the width of the plant measured in autumn. Those four entries turn vague impressions into something you can act on, and they are what tell you whether a poor flowering year was the weather, a late frost on the open buds, or something you did with the pruners nine months earlier.

If a mature plant flowers poorly two years running and has not been pruned late, look up rather than down. Overhanging tree growth that has closed in gradually is the most common cause, and it is easy to miss because it happens a little at a time.