When and How to Plant Garlic in Fall in Zone 6

Garlic is one of the few crops you plant in fall and forget until summer. Get the timing, depth and mulch right in October, and the cloves root before winter, sit out the cold, and come up as soon as the soil wakes in spring. This guide is written for zone 6 gardens and draws on extension advice from Penn State, Cornell, the University of Minnesota, Oregon State, Purdue and the University of Hawaii.

1. Time it by frost, not by the calendar

The University of Minnesota Extension and Cornell give the same rule: plant cloves one or two weeks after the first killing frost. Cornell adds that garlic is usually the last thing planted in the vegetable garden, after the first hard frost in early to mid-October. Penn State's master gardeners put the planting window at mid- to late October, and Penn State's fall-planting article adds a deadline from the other side: plant a good three weeks before the ground freezes.

Use your own first-frost date as the trigger. The cloves send out roots before the hard freeze, but shoots usually stay underground until spring, according to Minnesota Extension. That is what you want: roots without tender leaves going into winter.

2. Choose hardneck garlic and plant seed cloves

Penn State's Allegheny County master gardeners say hardneck (stiffneck) varieties grow best and are more cold-hardy than the softneck types used for braiding; Cornell calls hardnecks the most popular choice for its region too. Common hardneck groups are Rocambole, Purple Stripe and Porcelain; softnecks include Artichoke and Silverskin.

Buy cloves from a garlic seed producer, not the grocery store. Minnesota Extension warns that store garlic, mostly softneck, does not do well under Minnesota conditions, and Purdue notes that storage above 77 °F can inhibit bulb formation, which makes grocery garlic a poor bet for planting.

Elephant garlic, if you see it in catalogs, is a type of leek, not true garlic.

3. Prepare the bed

Garlic grows best in well-drained soil that still holds moisture, with a pH between 6.0 and 7.0 (Minnesota Extension). Test the soil first. Work in well-rotted compost or manure, never fresh manure, and loosen the bed so bulbs can swell.

Feed lightly at planting. Extension advice varies, so here is who says what:

• Purdue: about half a pound of 12-12-12 per 100 square feet, worked into the top 4 to 5 inches of soil.
• Cornell: ammonium sulfate and potassium sulfate, about 1 pound of each per 100 square feet; the sulfur helps garlic flavor.
• Minnesota: garlic has a moderate to high demand for nitrogen; work some in before planting, and you may not need more in spring if you added enough compost in fall.

If your soil test comes back high in phosphorus, Minnesota Extension recommends a low- or no-phosphorus fertilizer; it counts 10-10-10 among the high-phosphorus ones.

4. Plant the cloves

Break the bulbs into cloves a day or two before planting, and save the biggest cloves for the bed. Set each clove pointed end up.

Extension recommendations for depth and spacing overlap but do not match exactly:

Cornell notes the trade-off: plant closer and you get more garlic, but smaller cloves.

5. Mulch for winter

Cover the bed with 3 to 4 inches of straw or shredded leaves. Minnesota Extension gives three to four inches; Penn State's fall-planting article says a good four inches; Cornell suggests a few inches of straw a few weeks after planting. Mulch keeps soil temperature steady, stops freeze-thaw cycles from heaving cloves out of the ground, and holds back weeds.

Use straw free of weed seed. On a windy site, Penn State suggests laying branches over the bed to keep the straw in place.

6. Spring care

Once hard freezes are over, Minnesota Extension says you can pull the mulch back so the soil warms, or leave it in place for weed control and moisture.

• Feed: top-dress with nitrogen as soon as shoots emerge and again two to three weeks later. Stop after the first week of May, or bulbing may be delayed (Minnesota). Penn State's master gardeners simply say fertilize in March.
• Water: soak the soil to a depth of at least an inch each week, more often on sandy soil, and stop two weeks before harvest (Minnesota).
• Weed: early and shallow; young garlic cannot compete.
• Scapes: hardnecks send up a flower stalk, the scape. Oregon State recommends removing it in May or early June to increase bulb size; Minnesota suggests cutting scapes just after they start curling, and they are good to eat.

7. Harvest and cure

Expect harvest between late June and late July (Minnesota); Penn State gives early to mid-July and Cornell mid to late July.

Watch the leaves, then check a bulb:

• Minnesota: start when the lower leaves turn brown and half or slightly more than half of the upper leaves are still green.
• Penn State: harvest when the leaves begin to brown and at least four are still partly green.
• Oregon State: do not wait for the leaves to die back. Pull one plant and cut the bulb crosswise; it is ready when the head is divided into plump cloves and the outer skin is thick, dry and papery.

Too early gives small bulbs; too late and the cloves start popping out of their wrappers, which shortens storage.

Lift the plants with leaves attached, knock off the soil, and cure them somewhere airy and out of the sun. Minnesota Extension says a warm, dry, airy place for three to four weeks; Penn State's articles say a shaded, well-ventilated spot for two weeks to a few weeks. The bulbs are ready to store when the wrappers are dry and papery and the roots are dry (Penn State). Then trim the stems half an inch to an inch above the bulb and trim the roots. Keep the largest bulbs for next fall's planting.