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How and when to plant garlic
This article appears in the October 2010 issue of Growing for Market, and is typical of the practical, detailed information you will always find in GFM. Published 10 times per year, Growing for Market is available as a print magazine or an online subscription with access to an archive of more than 1,200 articles. Click here for more information about how to subscribe.
By Pam Dawling
In the May 2008 issue of Growing For Market I wrote about garlic harvest. This article is about garlic planting, which should be occurring soon on your farm. Although it is possible to plant softneck garlic in the very early spring if you have to, better yields are obtained by fall planting. And hardneck garlic is definitely better off if fall planted. In general, the guideline is to plant when the soil temperature at 4" deep is 50°F. The usual time for thermometer readings is 9 a.m. If the year is unusually warm, wait a week. (Instructions from Texas A&M say: less than 85°F at 2" deep.) We plant in early November, here in zone 7 central Virginia. In New Hampshire, mid-October is the time. The guideline for areas with cold winters is two to three weeks after the first frost and before the ground freezes solid for the winter. In California it can be planted in January or February.
Photo by Gayle M. Volk
If you miss the window for fall planting, ensure that your seed garlic gets 40 days at or below 40°F before planting, or the lack of vernalization will mean the bulbs will not differentiate (divide into separate cloves).
The garlic roots will grow whenever the ground is not frozen, and the tops will grow whenever the temperature is above 40°F. In colder areas, the goal is to get the garlic to grow roots before the big freeze-up arrives, but not to make top growth until after the worst of the winter. In warmer areas, the goal is to get enough top growth to get off to a roaring start in the spring, but not so much top growth that the leaves cannot endure the winter. If garlic gets frozen back to the ground in the winter, it can re-grow, and be fine. If it dies back twice in the winter, the yield will be decreased from the theoretical possible amount if you had been luckier with the weather. When properly planted, garlic can withstand winter lows of -30°F. If planted too early, too much tender top growth happens before winter. If planted too late, there will be inadequate root growth before the winter, and a lower survival rate as well as smaller bulbs.
Store seed garlic at 50-60°F. Avoid temperatures of 40-50°F during the summer, as this will cause sprouting before you are ready to plant. In other words, don't refrigerate. We keep our seed garlic on a high shelf in the shed from June to November and the conditions are perfect. If you need to store the bulbs over the winter, aim for 27°F. If you are buying seed stock, it is usually recommended to buy from a supplier in a similar climate zone. Having said that, I'll tell you that our hardneck garlic originally came from a bag of Chinese garlic bought at the wholesale produce market! We have been carefully selecting seed stock from this for about 20 years now, and it does great. Cloves for planting should be from large (but not giant) bulbs and be in good condition.
A yield ratio of 1:6 or 1:7 seems typical, and makes complete sense when you consider you are planting one clove to get a bulb of 6-7 cloves. If you achieve a yield ratio of 1:12 you are doing very well indeed. Divide the amount you intend to produce by six to figure out how much to plant. For large areas 750-1,000 pounds/acre are needed for plantings in double rows, 3-4" in-row, beds 39" apart. Eight pounds of hardneck or four pounds of softneck plants about 100 ft. In the US, one person eats 3-9 pounds per year. If you love growing garlic, move to Korea, where each person reportedly eats 60 pounds of pickled garlic each year.
Popping the cloves
The seed garlic bulbs should be taken apart into separate cloves not long before planting. We often do this while holding our annual Crop Review, with the crew coming together to collectively make notes on the past season. This task is a good group activity. Twist off the outer skins and pull the bulb apart, trying not to break the basal plate of the cloves, as that makes them unusable for planting. With hardneck garlic, the remainder of the stem acts as a handy lever for separating the cloves. We sort as we go, putting good size cloves in big buckets, damaged cloves in kitchen buckets, tiny cloves in tiny buckets, and outer skins and reject cloves in compost buckets. The tiny cloves get planted for garlic scallions.
Fusarium shows itself as small brown spots on the cloves, yellowed leaves and stunted browned roots. I learned from Dorene Pasekoff that Fusarium levels can be kept down by adding wood ashes when planting and then possibly dusting the beds with more ashes over the winter. (Don't add so much that you make the soil too alkaline.) To eradicate bulb or stem nematodes, if your seed stock could have these, soak separated cloves for 30 minutes in 100°F water containing 0.1% surfactant. Soak for 20 minutes in the same strength solution at 120°F, then cool in plain water for 10-20 minutes. Allow to dry for 2 hours at 100°F or plant immediately.
Garlic does best with a sandy or clay loam with very good drainage and a pH of 6.0-8.4, with 6.8 optimum. Onion maggots thrive if the soil is alkaline, so it pays to watch the acidity. A rotation of at least five years away from alliums is a good practice to reduce the likelihood of disease. Generally 1-2" of water per week during the growing season (not during the winter), is about right, until the leaves start to yellow and the bulbs start to dry down, when irrigation should be stopped.
Fertile soil with lots of organic matter and a full range of nutrients is needed to grow good garlic, and so is full sun. Most growers spread compost or soybean meal at planting time. Foliar feeding, although recommended by some sources, provides no gain in yield if the soil had adequate fertility at planting time. Also, it is technically tricky to get foliar fertilizers to stick on the waxy near-vertical garlic leaves - it tends to run off, so a good spreader-sticker is essential. And foliar feeding (or side-dressing with compost or organic fertilizers) is wasted after the fifth leaf, and certainly after the bulb starts to enlarge. If soil fertility is uncertain, northern growers may feed every two weeks in early spring until there are four leaves. In the south, spring is too late for foliar feeding, as garlic reaches a four-leaf size before winter. It is unwise to over-fertilize in the fall or the growth will be too fast and tender to survive cold conditions, and the storage life of the garlic will be reduced. So if your garlic typically reaches four leaves before winter, forget about foliar feeding and side-dressing.
Spacing and depth
We plant at 5" spacing in the row, and 8-10" between rows, usually with four rows in a bed. The beds are 3.5-4 ft wide. That's 40 sq. in. each. 32 sq. in. is a minimum, and 72 is recommended for very large bulbs (which might win ribbons at the fair, but might not give you the highest yield for the area). Many growers plant at 6" in-row. Research was done at Colorado State University Specialty Crop Program 2004 and 2005:
They found that 3" was too close. The shading of one garlic by another reduces the yield. For best use of drip tape, you can run a length of tape and plant a double row, one row each side, with all plants 6" apart in all directions, and 40" or less between drip lines.
Cloves are usually planted with 1.5-2" of soil over the top of the cloves in the south, and 3-4" of soil in the north. (The deeper planting helps prevent too much top growth and also moderates the soil temperature the clove is growing in.) In Arizona, some growers set the cloves on the soil surface, then cover with 6" straw. This makes for a clean crop and an easy harvest. Organic mulch can be added immediately after planting, or if you live in a colder area than we do, after the tops get frosted off. In Michigan, planting time is six weeks prior to the ground freezing, giving enough time for root growth only, to avoid freezing the leaves. Planting depth there is 6". Avoid planting deeper than necessary, as you may get worse mold problems.
Do ensure the cloves are planted the right way up, if you are planting a hardneck variety! Hardneck cloves planted with the points down suffer a 30% reduction in yield. Softneck cloves can be planted any way up, so are easier for mechanical planting. Our method is to make furrows with pointed hoes, then lightly press the cloves into the furrows at the chosen spacing, using pre-cut measuring sticks. After that we pull soil over the cloves using regular hoes or rakes, and tamp the soil down with the back of the tool. Some other growers who also plant by hand make a planting jig to make four or more holes at a time in loose soil, rather than make a furrow. A clove is then planted in each hole and covered with the right depth of soil.
If you can't squat to hand plant, or you are planting from the seat of a tractor, use a 3' length of pipe to drop the cloves into the furrows. Dropped from that height, through a tube wide enough for the garlic to tumble end-over-end, the cloves will land the way they need to be.
I read a fascinating article in the Natural Farmer, Fall 1992: Grace Reynolds of Hillside Organic Farm in New York converted a Cole one-row corn planter on the toolbar of her tractor to plant garlic. She attached a long tube to the planter and an angel food cake pan to the top of the tube. She sets the tractor in crawler gear and walks behind it dropping cloves through the pan into the tube. She also added a mark on the turning plate in the corn planter, so that she drops a clove down the tube each time she sees the mark, giving a regular spacing.
There were efforts in Virginia in 2003-2005 to develop no-till planting methods for garlic, planting in the fall into a frost-killed cover crop. sorghum-sudan hybrid, lab-lab bean and sunn hemp were planted in the first week of August in raised beds. As soon as frost had killed the cover crops (October 24) the beds were rolled to flatten the crop residue, and garlic cloves were planted 5-6" deep in holes made with a soil probe. (This seems surprisingly deep to me.) Some plots were then covered with thick straw. All were given organic fertilizers. The disappointing results were that no-till caused a 32-44% bulb loss, with sorghum-sudan by far the worst. So don't reinvent the wheel on that one. The speculation was that the cover crop residues tied up the available nitrogen. Adding straw mulch was found to be beneficial, always.
David Stern in upstate New York successfully plants into oats that have reached 6" tall. He cuts slots through the oats with a disc-furrower and plants the cloves in the slots. The oats continue to grow until winter-killed, and they continue to protect the garlic. Timing is obviously critical and site-dependent.
Mulching or not
We like to roll round bales of spoilt hay over our beds immediately after planting. We come back a couple of weeks later and free any shoots trapped by clumps of over-thick mulch. Then we leave it all alone until late February, when we start weeding (once a month for four months). Organic mulches in the south help keep the soil cool once the weather starts to heat up. It is also possible to add mulch after the garlic has started to grow. This is more difficult than rolling bales across the bed, but if you have planted while it is still warm and you want to allow the soil to cool before mulching, in order to prevent too much top growth before winter, this is an option. Myself, I would just plant later.
Organic mulches will protect the cloves from cold winter temperatures to some extent. It is also possible to use thick row cover to protect garlic over the winter, even a double layer of row cover in very cold areas - whether or not you use mulch..
Yet another option is to over-sow the garlic plot with oats to hold the soil and reduce erosion. The oats grow in the early winter and then die at 18-20°F, and the dead plants continue to hold the soil in place. Because the oats are sown after the garlic is planted, this involves sowing oats much later than you would for a good stand as a winter cover crop. An alternative is to no-till plant into oats which are growing.
As with all alliums, removing weeds is important. Yield can decrease by a phenomenal amount (as much as 50% in total). Because garlic is an overwintering plant in most regions, it will be necessary to kill the spring cool-weather weeds, and later kill the summer weeds.
Growers not using mulch will need to cultivate fairly frequently to deal with weeds. Hillers will deal with the between-row weeds and some of the in-row weeds, but be careful not to cover too much of the leaves as this will reduce yields. Many growers use hand hoes and those with mulch will hand weed. Keep the leaves in good shape as best you can - take care when hoeing or cultivating. Each leaf damaged or removed will cause about a 17% yield reduction.
Five applications of 10% acetic acid vinegar spray during the growing season has been shown to be a useful technique in controlling broadleaf weeds, but has no effect on grass weeds. Start when the garlic is 18" tall and spray about every 10 days. Spraying from both sides of each row is the most effective. Wear a mask and gloves, as well as long sleeves and long pants when spraying this caustic strength of vinegar. It is possible to reduce labor by 94% using vinegar rather than hand weeding, so if broadleaf weeds are what you get, this is a good solution. See the 2004 SARE Grant report by Fred Forsburg.
Growers who prefer not to mulch need to start weeding sooner. Flame weeding can achieve as good results as hand weeding using one-third of the labor. Flame weeding can be used for relatively mature garlic, but young plants (four or fewer leaves) are too easily damaged. The flame is directed at the base of the plants, in the morning, when the plants are turgid. Naturally, if you have used straw or hay mulch, flame-weeding is not such a smart idea!
Diseases and pests
The major diseases are mostly fungal: White Rot, Fusarium, Botrytis, Rust, Penicillium Molds, Purple Blotch, Powdery Mildew, Downy Mildew. Bacterial soft rots are also sometimes seen. Remove isolated moldy plants as soon as you see them. Always remove garlic debris from the field at the end of the season, or till it in and plant a non-allium crop. In summer, soil biological life is very active, and soil organisms will quickly break down the debris.
White Rot is most active below 75°F, and leads to yellowing and dying of older leaves, tip burn, and then destruction of the root system and rotting of the bulb. This fungus can persist in the soil for 10 years, and requires assertive action to reduce the problem. A clever trick is to spray garlic extract on the soil when the temperature is 60-70°F and you have no garlic growing. The fungal mycelium may grow and then die off in the absence of food. Several weeks later, garlic can be planted and will escape the rot.
Fusarium usually attacks plants that are under stress. In our garden it is the plants on the gravelly edge of the patch which get this disease. It grows during hot weather, with symptoms similar to White Rot, but slower to develop. The browning of the leaves spreads from the tips. Good sanitation and fostering strong plant growth are the main organic approaches to controlling Fusarium.
Botrytis symptoms include "water-soaked" leaves, and can lead to bulbs rotting, sometimes during storage. This fungus grows best (worst!) in warm wet weather. Good air flow during growth, curing and storage will reduce the chances of Botrytis problems.
Rust shows up initially as small white flecks on the leaves, developing into orange spots. Favorable conditions include temperatures of 45-55°F, high humidity but low rainfall, and low light. Stressed plants are the most likely to be stricken. Infected bulbs may shrink, yellow and die. Once again, good sanitation and rotations are the organic approaches.
Pests include nematodes, thrips, onion maggots, cutworm, armyworm, and mites. Weekly scouting is a good practice.
Nematode infestations show up as distorted, bloated, spongy leaves and bulbs, perhaps with brown or yellow spots. Top growth yellows and may separate from the root system. Farmscaping (planting flowers which attract beneficial insects which also feed on your pests) can work for thrips, which are on the menu for lady bugs and minute pirate bugs. Beneficial nematodes have been shown to be effective against onion maggots, and ground and rove beetles, birds and braconid wasps all prey on some life stage of the maggot. Row covers can exclude the fly (mother of the maggots).
The end of growth
The start of bulb formation (and the end of leaf growth) is triggered by day length exceeding 13 hours (that's April 10 here in central Virginia on the 38th parallel), with temperatures above 68°F as a secondary trigger. Hot weather above 91°F will end bulb growth and hasten maturation or drying down. Therefore, it is important to get plenty of good rapid growth in before the plant dies back. In warmer areas, temperatures will thus exert a bigger effect on harvest date than in cooler areas, where the day length will have a bigger impact. For example, in Michigan, bulbing begins in mid-May, almost entirely triggered by the day length.
Garlic can double in size in its last month of growth, and removing the scapes (the hard central stem) of hardneck garlic about 3 weeks before harvest can increase the bulb size 25%. Watering should stop two weeks before harvest (one week after starting to harvest scapes), to help the plants dry down.
Growing Great Garlic by Ron L. Engeland.
ATTRA publication Organic Garlic Production.
The Garlic Seed Foundation, an informal organization of growers and eaters, also has good information.
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Pam Dawling is garden manager at Twin Oaks Community in Louisa, Virginia. The gardens provide the 100 residents with virtually all of their fresh and preserved produce each year.