It's Not Too Late to Plant Garlic!

Gardeners have many beliefs about when to plant garlic. The moon planting folks like the night of October’s first full moon, which always feels magical, or the third quarter, because the waning moon is supposed to stimulates root growth with its downward pull.

This year, those dates would have been October 7 and 13, about a month too early for planting garlic in most temperate climates. Seed garlic that is planted while the soil is still warm can quickly grow green tops, which are often killed back by harsh winter conditions. A few inches of winter tipburn is one thing, but garlic that is nipped back more than once is less likely to produce big, perfect bulbs in early summer.

The Best Time to Plant Garlic

It's much better to wait until soil temperatures 4 inches (10 cm) below the surface drop to 50°F (10°C) when measured between nine and ten in the morning. At this temperature, seed garlic quickly strikes roots, but is not triggered to grow green shoots. The cloves slowly develop roots for a month or more, and then enter their vernalisation phase as soil temperatures in the root zone fall to 40°F (4.4°C) or below and stay there, despite warm or frozen conditions at the surface. After eight weeks of serious chilling, the rooted cloves are ready to grow into plants.

Why all these details? Because of climate change, which is raising soil temperatures, especially in autumn. Warmer summer soil is slower to cool down, and the onset of winter is delayed in many climates as well. Both have a direct bearing on garlic, which is grown from fall to spring.

For example, in the UK, data gathered over the last 80 years by the University of Reading shows a rise in soil temperatures of 1.5C (3°F), with suitable temperatures for planting garlic now stretching into December. Longer autumns also are happening in North America, such that seasoned garlic growers like Pam Dawling delay planting until November in USDA Zone 7.

Autumn vs Spring Planting

Late planting allows more time to properly prepare a planting bed, which must be fertile and well drained for good garlic. In winter, the main job of garlic cloves is to grow roots, all of which emerge from the base of the clove. Amending the root zone with compost and a balanced organic fertiliser ensures plenty of available nutrients, which won’t be washed away by winter rains when they are well buried. Late planting also may reduce problems with allium leafminers, which lay eggs on tender young garlic leaves during spells of mild winter weather.

How late is too late? In a trial in frigid Minnesota, garlic planted in November was subject to winter injury, but not all varieties were bothered. In the Minnesota study and others, Chesnok Red and other purple stripe garlic strains from Northern Europe showed better vigor under cold conditions.

Just don’t wait until spring if you want the biggest bulbs. A two-year study in Missouri showed little negative effect to planting garlic in early November, while garlic planted in February produced little bulbs with puny cloves. Even when seed garlic is kept chilled through winter to simulate vernalisation, spring-planted crops never catch up.

You can certainly plant garlic in large weatherproof containers where the plants can grow undisturbed through winter, but don’t try starting cloves in small pots and transplanting them. Like beetroot and poppies, new garlic roots are incredibly sensitive and rarely recover from moving about, even when lifted with care.

Should You Mulch?

Regardless of planting date, garlic always benefits from mulch. Grass clippings, straw, shredded leaves or even strips of cloth make good garlic mulches, which suppress weeds while keeping the soil cool and moist. In addition, mulches cushion the soil from compaction caused by heavy rain, which is important with garlic, which can suffer under waterlogged conditions. Mulches also insulate the tender young shoots from cold injury, and may reduce issues with fusarium and other common garlic diseases. When it comes to garlic planting, mulch is the icing on the cake.

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