Growing lettuce, endive and radicchio in home gardens

• Have your soil tested. 
• The best pH range for lettuce and chicories is between 6.0 and 6.8.
  • Apply phosphorus (P) and potassium (K) according to soil test recommendations.  
  • Many Minnesota soils have enough phosphorus. Unless your soil test report specifically recommends additional phosphorus, use a low- or no-phosphorus fertilizer.
• Improve your soil by adding well-rotted manure or compost in spring or fall. Do not use fresh manure as it may contain harmful bacteria and may increase weed problems. 
• The soil should be well drained and moisture retentive. Till the soil deeply, and then smooth the surface.
• Use a complete fertilizer such as a 10-10-10, at the rate of two pounds per 100 square feet.
• When the plants are about four inches tall, apply a side-dressing of the same fertilizer at a rate of one pound for each 25 feet of row.
• Do not use any fertilizer containing a weed killer ("Weed and Feed"), as it may kill your vegetable plants.

• Non-heading: loose-leaf, including oakleaf and lolla
• Soft heads: butterhead and bibb
• Ruffled heads: French crisp, summer crisp, or Batavia
• Tall, compact heads: cos or romaine
• Dense, solid head: crisphead or iceberg

Loose-leaf varieties are easiest to grow.  

Chicories are close relatives of lettuce, and you can grow them in similar ways. The coffee substitute called chicory comes from the dried roots of these plants. Try these varieties to add color and texture to your garden and flavor to your salads.

• Endive is a versatile salad and cooking green. Mild and sweet, with slight bitterness, curly endive is a common salad green.
• Escarole is a form of endive with broader, smoother leaves.
  • Recipes usually call for cooked escarole.
• Belgian endive is an expensive winter specialty.
  • In fall, dig up Belgian endive roots and store them in a root cellar. Give them complete darkness to produce small dense heads of pale leaves.
  • It is very difficult for a home gardener to grow Belgian endive successfully.
• Radicchio forms dense, bitter heads.
  • Plant in summer for fall harvest. Treat it the same as endive or lettuce.
  • Radicchio needs about 60 to 70 days to mature, much longer than lettuce or endive.
  • Although radicchio has some cold hardiness, it may not form a head before winter comes.
• Italian dandelion is another form of radicchio, a bitter green for salads or cooking. It is easy to grow.
  • Direct seed Italian dandelion in spring, summer or fall.

Lettuce and chicory seed are very small and difficult to see.

Starting seeds indoors gives you the chance to handle the seed in controlled conditions while it is still cold outside, as well as during the heat of the summer.

Indoor air temperatures, easily managed fertility and water, and bright lights on a timer will produce strong plants. You can space young plants correctly in the garden without stooping to hand thin.

To direct seed lettuce, it is important that you prepare the soil ahead of time.

• A cloddy, clumpy seedbed will reduce seed germination and emergence.
• Seeds of these plants are very small.
• It is easy to seed these crops too heavily or too deeply.
• The raw, untreated seed is difficult to see and handle.

Consider buying pelleted seed.

• Inert clay-based material coats pelleted seeds and increases the size of the seed.
• They are easier to plant sparingly and precisely.
• The seed coating can also help with germination by taking up water and conducting it to the seed.

Although the price of pelleted seed is higher than the unmodified seed, many gardeners get better results with less effort when they use prepared seeds.

Place the prepared seeds evenly every two to four inches. You will waste less seed and reduce the need to thin the plants as they grow.  

If using unmodified seed, seed lightly and evenly down the row.

• Sow seeds in the spring as soon as the soil is workable.
• For a fall crop, sow seed about three months before the average first fall frost date.
• Plant seeds 1/4 to 1/2 inch deep, in rows 18 to 30 inches apart.
• Thin the seedlings when they are still small. Try to do this without damaging the remaining plants.
• Clip off unwanted plants with a pair of small shears to avoid disturbing the other plants.
• Final plant spacing depends on the variety. Rows should be at least 18 inches apart.
• Loose-leaf lettuces can fill a wider spacing in fall, when the plants are likely to grow well and are less likely to bolt.
• When bolting, the plant sends up a flowering stalk and stops growing.

• Purchase transplants from a garden center or grow your own by planting seeds indoors in early April or about four weeks before transplanting.
• For fall crops, plant seed in July.
• Harden seedlings by reducing water and temperature for two to three days before transplanting.

Blanching endive will grow white leaves in the heart of the plant and prevent excessive bitterness.

About a month after transplanting, or six weeks after direct seeding, carefully tie the outer leaves up around the heart of the plant with string or rubber bands.

Blanching takes about two weeks.

If you space the plants closely, they will develop more upright growth and will self-blanch to some degree.

Both lettuce and the chicories do best in cool weather. Ideal conditions are a nighttime low temperature of 50°F, and up to a 68°F daytime high temperature.

Along the Lake Superior shore and in other cool parts of the state, you can grow lettuce and endive during most of the summer.

For most places in Minnesota, June, July and August conditions are too hot for these crops.

These plants may bolt in response to long days, high light intensity, and heat. Bolting causes extreme bitter flavor.

While lettuce breeders continue to grow varieties that are slow to bolt, there is always a chance that a planting will flower. Bolting ends the possibility of harvest.

• Watering is important to grow these salad crops, as they have small, shallow root systems.
• One inch of rainfall per week is adequate.
• If your soil is sandy, it is better to water more often than once a week.
• An inch of water will wet a sandy soil to a depth of ten inches, a heavy clay soil to six inches.
• Use a trowel to see how far down the soil is wet. If it is only an inch or two, keep the water running.
• When rainfall or watering follows a dry spell, the plants will suddenly resume growth. This leads to “tipburn,” or the browning of the leaves.
• Lettuce, endive and radicchio will be crisper if you water them often in the days prior to harvesting.

• Frequent, shallow cultivation with a hoe or hand tool will kill weeds before they become a problem.
• Scratch the soil just deeply enough to cut the weeds off below the surface of the soil. Be careful not to damage the plants when cultivating.
• Mulching with herbicide-free grass clippings, weed-free straw, or other organic material to a depth of 3 to 4 inches can help prevent weed growth, decreasing the need for frequent cultivation.

• Harvest single leaves as soon as they reach a usable size.
• If you harvest individual leaves at the "baby" stage, leaving most of the small leaves on the plant, multiple harvests are possible.
• You can also remove the whole plant by cutting it off at or just above the soil surface.
• For the spring crop, flavor is best if you harvest the plants before the weather becomes hot and dry.
• Heat will slow growth and the leaves will become tough and bitter as the plant bolts.
• For the fall crop, the cooler the weather, the better the flavor.
• Freezing temperatures stop growth.

• Cutworms can cut young plants off at the base.
• Snails and slugs may cause holes in the leaves.
• Flea beetles chew many small, round holes in leaves.

Aster yellows is a disease of many garden plants spread by leafhoppers, small insects that feed on plant juices. Symptoms include stunted, yellow plants.

• Lettuce leaves can develop a bitter taste if exposed to periods of hot weather.
• Multiple days of high temperatures (greater than 75° F) can cause lettuce plants to flower. This is often called bolting.