Lingonberry

Plant with a second cultivar as a pollinizer

Plant in spring as soon as the soil can be worked, in full sun, setting roots 2 to 3 inches deep and spacing plants 8 to 18 inches apart. Add a second cultivar such as Red Pearl or Sussi at roughly one plant in ten, and keep it near the others so bees will move between them. Fall planting also works. Lingonberry will set some fruit on its own, but the berries stay small. Pollen from a different cultivar, carried by bumblebees, honeybees, and flies, is what produces full-size berries and the highest yield, and it is needed for both the spring and the summer bloom.

⚠ Wind does almost nothing to pollinate lingonberry, so a sheltered site with active insects matters more than airflow. Heavy rain or high wind during bloom hampers pollination.

About half an inch a week, and never bone dry

Apply 0.5 to 0.75 inch of water a week, by drip if you can manage it. Water without fail through the first summer after planting to establish the roots and prevent sunburn. On heavier soil, hold back rather than push. Two opposite mistakes kill lingonberry. Letting the soil dry out concentrates salts in the soil water, which this species tolerates very poorly. Overwatering a heavy soil invites Phytophthora root rot and Pythium, which is exactly how Koralle plantings died in Oregon trials.

⚠ Test irrigation water for pH, chloride, sodium, and calcium before relying on it. Lingonberry is damaged by even modest chloride and sodium levels.

Renew the acid mulch each spring

Keep at least a 2 inch layer of peat moss, partially decomposed sawdust, or bark mulch over the root zone each spring, and renew the deeper 4 to 6 inch planting mulch every 3 to 6 years as it breaks down. Lingonberry roots run right at the soil surface, so mulch is what holds moisture and smothers weeds. It matters because the alternative does not exist here: cultivating deeply enough to control weeds would shred the very roots you are trying to feed.

⚠ Do not use preservative-treated wood mulch.

Feed lightly in spring, ammonium nitrogen only

Give one light spring feeding of nitrogen in the ammonium form: urea, or ammonium sulfate where the soil pH also needs pulling down. Commercial rates are only 20 to 40 pounds of actual nitrogen per acre through the first five years and about 40 pounds a year after that, so at garden scale this is a scattering, not a handful. When in doubt, give less. This is a lean boreal heath plant. Nitrogen above roughly 60 pounds per acre pushes leafy growth at the expense of flowers and actually reduces the crop, and overapplication causes a brown-to-black dieback that looks so much like Phytophthora root rot that growers misdiagnose it as disease.

⚠ Use only chloride-free fertilizer. Chloride salts severely damage lingonberry, and high sodium or calcium is also toxic. Koralle and Red Pearl are more sensitive to high rates than other cultivars.

Leave it unpruned for five years, then mow alternate rows

Do not prune at all for the first four or five years after planting. Once the planting is five years or older, cut alternate rows down to about 2 to 3 inches above the mulch in very early spring, and repeat every 3 to 6 years. Never cut the whole planting in one year. Lingonberry blooms on the tips of last year's growth, so cutting removes the coming crop outright. It also stimulates dense, vigorous, unbranched one-year wood that carries many more fruiting stems the following season. Alternating rows buys that renewal while leaving half the planting in bloom wood.

⚠ Extension notes there is still no established best practice for pruning lingonberry, so treat the mow as renewal on a long cycle rather than annual maintenance.

Cover open flowers when frost threatens

If frost is forecast while the bell-shaped flowers are open, cover the planting with floating row cover or run overhead irrigation through the freeze. Take covers off once temperatures rise so pollinating insects can reach the flowers. Frost at temperatures as mild as 28F damages lingonberry flowers and prevents pollination and fruit set, and a freeze during flowering or fruiting can cost up to half the berries. The damage is to the flower itself, so once it is done there is no second chance at that crop.

Protect only when hard cold arrives without snow

Where winter temperatures drop below about 10F and snow cover is thin or absent, protect plants with straw mulch, floating row cover, or overhead irrigation. Under reliable snow, do nothing. Lingonberry has come through 2F unharmed in Oregon, Washington, and Wisconsin plantings. Snow is the insulation this species evolved under, so it is bare, snowless cold that injures the evergreen leaves and buds, not low temperature by itself.

Take the fall crop dark red, after a sharp frost

Pick when the berries are light to dark red; any green left on the fruit means it will taste bitter. Favor the fall crop and let the lighter summer crop go, and pick it after a sharp frost. A hand rake of the sort used for lowbush blueberries and dry cranberries works well. Refrigerate at 32 to 45F: extension figures for clean, not-overripe fruit range from 3 to 5 weeks for fresh-pack shipping (PNW 583-E) up to 8 to 12 weeks (Cornell). Freezing holds the fruit for many months. The summer berries drop from the plant by the fall harvest anyway, and the fall crop is both heavier and better quality. The fruit's own high benzoic acid content is what gives it an unusually long shelf life once picked.

⚠ A frost just before harvest does not hurt fruit on the plant, but a prolonged freeze will destroy the crop. Berries left too long are overripe, will not store, and should be processed at once.