Growing tomatillos and ground cherries in home gardens

• Have your soil tested. 
  • 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. 
• Ground cherry plants may not need more fertilizer.
• Tomatillos and ground cherries need about the same amount of nitrogen as any other crop.
• Too much nitrogen fertilization will lead to plants that are bushy, leafy, and slow to bear fruit.
• Do not use any fertilizer containing a weed killer ("Weed and Feed"), as it may kill your vegetable plants.

There are few cultivated varieties of tomatillo, and none has undergone formal trial in Minnesota. There are no tomatillo varieties grown specifically for northern gardens.

• Purple (1 ½-inch fruit, sweeter flavor)
• Green, also called Verde (2-inch fruit)
• De Milpa (1-inch fruit, tangier flavor)
• Tamayo (3-inch fruit)

The ability of a single tomatillo plant to set fruit may depend on the species and variety. Grow more than one plant for best fruit set. Cross-pollination between two plants of two different varieties is ideal.

Ground cherry varieties are also limited. ‘Goldie,’ ‘Pineapple’ and ‘Aunt Molly’s’ are all good for growing in Minnesota gardens. All have a distinctive, sweet and tangy flavor.

Start ground cherry seeds indoors six to seven weeks before planting outdoors. Start tomatillos only four to five weeks before setting out, a week or two later than tomatoes.

If you set tomato plants out at the end of May, sow ground cherry seeds in early April, tomato seeds on the fifteenth and tomatillo seeds at the end of the month.

1. Plant seeds one-fourth inch deep in flats containing sterile, soilless germination mix. Use a heating mat to keep the flat at 75°F to 85°F until seedlings emerge.
2. After emergence, a soil temperature of 70°F is ideal. Warm soil is better than cool. Monitor potting mix moisture, as heating mats will dry the mix faster.
3. Provide bright overhead light for the seedlings.
4. Thin or transplant seedlings after true leaves appear so that seedlings are two inches apart. Grow plants under bright light.
5. A week or so before you plan to set the plants out in the garden, reduce watering.
6. Place plants outside where they will receive a couple of hours of sunlight and wind protection.
7. Expose plants to more and more sunlight over the next week or two. Bring them indoors if night temperatures are below 55°F.
8. Transplant to the garden after all danger of frost has passed and the soil has warmed.

Allow ground cherry plants 18 to 24 inches of space in all directions.

Tomatillos need more space, as much as three feet, because of their bushy habit. Plan to trellis, cage or otherwise support tomatillo plants. Allow enough space between plants for good air circulation. If plants begin to crowd each other, prune them back. 

Many gardeners use season-advancing techniques such as plastic mulch and plant covers to get a head start on planting heat-loving plants. Plastic mulches, hot caps, water-filled insulators, and tunnels or supported row covers all help northern gardeners raise heat-loving plants.

• Tomatillo and ground cherry plants have strong root systems. They can withstand drought and heat. Keep soil moisture levels even to grow uniform, high quality fruits.
• Avoid overhead sprinkling. Wet leaves are more disease prone. Soil splashed up onto the leaves can contain disease spores.
• One inch of rainfall per week is good.
• Soak the soil thoroughly when watering, once or twice a week. If your soil is sandy, 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.

• Weeds may reduce air circulation through tomatillo leaves, leading to leaf diseases.
• Tomatillos plants are good competitors to weeds. They grow quickly in warm weather and shade out weed seedlings.
• Frequent, shallow cultivation with a garden hoe or trowel will kill weeds before they become a problem.
• Cultivate just deeply enough to cut the weeds off below the surface of the soil. Be careful not to damage the vegetable plants.
• Mulching with herbicide-free grass clippings, weed-free straw or other organic material to a depth of three to four inches can help prevent weed growth, decreasing the need for frequent cultivation.

• For assistance in diagnosing unknown problems, visit the University of Minnesota Extension diagnostic site “What’s wrong with my plant?”

• Temperatures above 90°F or below 55°F can cause flowers to abort.

• Too much nitrogen can cause the plant to grow more leaves than flowers.

• Cutworms chew stems of young transplants at the soil line, leaving the severed tops uneaten. 
• Tomato hornworm and the Colorado potato beetle feed on these plants.

• Tomatillos and ground cherries are vulnerable to many of the diseases that affect potatoes, tomatoes, peppers, and eggplant. These diseases can overwinter in the soil and affect the next year’s crop.
• Practice crop rotation. Use good cultural control practices to reduce disease problems to a tolerable level and allow for a successful harvest. 
• Rainy periods or humid windless days can encourage foliar diseases.
• Early blight, anthracnose, late blight and tobacco mosaic virus can affect tomatillos. 
• Verticillium wilt can cause yellowing and wilt in tomatillos and ground cherries.

Harvest

• For the highest quality fruit and best flavor, pick tomatillos when the fruit fills the husk, but while still green and firm. If left on the vine beyond this stage, the fruit will continue to ripen, become soft and develop a bland flavor.
• When fully ripe, ground cherry husks will be dry, and the fruit will drop from the plant.  A mulch of clean, weed-free straw will keep the fruits clean if they drop.
• Both tomatillo and ground cherry self-seed in the garden.
• It is a good idea to clean up any fallen fruit even if you do not intend to eat it, so that you will not have to deal with all the volunteer plants next year.

Storage

Tomatillos can last for months in a cool, well-ventilated place: 50°F to 60°F, with 60% relative humidity.

Spread fruits one layer deep, still in their husks. The fruit will spoil rapidly if placed in an airtight plastic bag for storage, but a paper bag of fruit can keep in the refrigerator for two weeks. After two weeks, chilling injury will lead to pitting of the skin and spoilage.

You may also can tomatillo fruits, or freeze them just like berries. In a dry, unsweetened pack, remove the husks, wash, dry and spread in a single layer on a baking sheet. Freeze until solid, then transfer to bags and seal.

If left in the husk, ground cherries will keep for a week or two. Because their fruits are truly ripe when picked, they have a shorter shelf life than tomatillos. You can keep ground cherry fruit as jam or preserves. You may also can or freeze them like tomatillos.