Sign up for the
Weekly Harvest Newsletter!

Published every Wednesday, the Weekly Harvest e-newsletter is a free Web digest of sustainable agriculture news, resources, events and funding opportunities gleaned from the Internet. See past issues of the Weekly Harvest.
Sign up here

Sign up for the Weekly Harvest Newsletter

What Is Sustainable Agriculture?

Master Publication List

Search Our Databases

Urban Agriculture

Energy Alternatives

Beginning Farmer

Field Crops

Horticultural Crops

Livestock & Pasture

Value-Added Food Products

Local Food Systems

Food Safety

Marketing, Business & Risk Management

Organic Farming

Pest Management

Soils & Compost

Water Management

Ecological Fisheries and Ocean Farming

Other Resources

Sign Up for The Dirt E-News

Home Page

Contribute to NCAT


Newsletter sign up button

· Privacy Policy · Newsletter Archives

RSS Icon XML Feeds

RSS 2.0: Events, Breaking News, Funding Opportunities Atom: Events, Breaking News, Funding Opportunities


NCAT strives to make our information available to everyone who needs it. If you are a limited-access or low-income farmer and find that one of our publications is just not in your budget, please call 800-346-9140.


How are we doing?


Home  > Question of the Week

Question of the Week

Permalink Can you tell me what the cross-pollination needs are for certain apple, pear, and berry varieties?

Answer: Apples should not present a problem. Arkansas Black is considered to be mostly pollen-sterile. Either the Enterprise or Williams Pride can pollinate it, but it can't pollinate anything. But you have three different varieties, so the Enterprise and Williams Pride will pollinate each other, as well as the Arkansas Black, so everything gets pollinated. By the way, the Williams Pride will start blooming most years a few days ahead of Arkansas Black and Enterprise, but there is plenty of overlap.

The potential problem lies with the pears. Like Arkansas Black apple, the Magness pear is understood to have mostly sterile pollen. It can be pollinated by the Shinko, but it cannot reciprocate. It might not be a problem if there are any other pears within two to three miles, but if you don't know if there are other pears in the vicinity, you should probably consider switching the Magness or adding a third pear to the mix. Since there are no more pollen-sterile pears, any pear would work.

Juneberries, raspberries, mulberries, and blackberries don't need cross-pollination, so you should be fine in that respect. Peaches and tart cherries are also self-pollinating. American persimmons need a male tree, but since there are so many around, that is rarely ever a problem. Japanese persimmon pollination is interesting and you can learn more about this in the ATTRA publication Persimmons, Asian and American, available at Blueberries do better if there are other varieties around, but cross-pollination is not essential.
ATTRA has several publications that can help you learn more about fruit production, including pawpaws, persimmons, pears, peaches, plums, apples, bramble fruits, and strawberries.

For more information on topics related to pollination, refer to the following ATTRA publications:

Tree Fruits: Organic Production Overview

Alternative Pollinators: Native Bees

Companion Planting: Basic Concepts & Resources

Send feedback » Permalink


Permalink Can I plant a cover crop with my asparagus for weed control?

Answer: The ATTRA publication Organic Asparagus Production addresses some of the research that has been done in this area. From the following information excerpted from that publication, however, doing so appears to be quite management-intensive.

Cover crops
Cover crops are another useful tool in asparagus weed management. Two cover crop systems that have potential in asparagus are "dying mulches" and "living mulches."

Dying Mulches
A dying mulch is a cover crop planted out of season. While growing it suppresses weeds; then it dies back out on its own without requiring the use of herbicides, mowing, or tillage. Winter rye—planted in the spring—has been used successfully in this manner in several agronomic and horticultural crops.

In asparagus here's how this might work. Following post-harvest tillage of the asparagus field, the field is over-seeded with winter rye at 120 pounds per acre to establish the living mulch. Since the winter rye is planted in late spring and consequently does not receive normal winter vernalization (cold treatment), it never tillers (i.e., it stays short) and eventually "cooks out" by mid-summer. By this time, the asparagus ferns form a thick canopy that shades out most underlying weeds.

The success of this system is dependent on proper timing and good luck. Timing is critical to get the rye established early enough to promote germination when the soil temperatures are still relatively cool, but at the same time, late enough that a cold spell is avoided. Vernalization can occur when the rye is exposed to only 10 days of 45° F nighttime temperatures.

Dr. Astrid Newenhouse, formerly with the University of Wisconsin, conducted cover crop research in horticultural crops and provided some preliminary insights into dying mulch and living mulch systems for asparagus. Dr. Newenhouse tried the non-vernalized rye system described above. She agreed that timing was critical with respect to a cool spell. As a result of a cold snap one year, her rye headed out and created additional management problems.

Living Mulches
Living mulches are cover crops grown in association with annual or perennial crops, primarily for weed suppression and as a soil management practice. The goal is to plant a low-growing cover that suppresses weeds without competing too much with the main crop.

In Wisconsin, Dr. Newenhouse's living-mulch work in asparagus focused on two cover crops: perennial ryegrass and 'Dwarf White' Dutch white clover. Both cover crops were fall-established and managed the following growing season with one to three mowings using a walk-behind sickle-bar mower. Preliminary results indicated that perennial ryegrass performed better than the Dutch white clover the first growing season. However, in the second growing season these results were reversed, with the Dutch white clover performing better. This research found that living mulches could be highly effective in weed suppression but also quite competitive with the crop, reducing asparagus growth 50 to 75% in some instances. Clearly, more research is required to find living mulch systems that are more viable."

The living mulch system, while it controls weeds, appears to compromise the asparagus yields too much to be economical.

Organic Asparagus Production is available at

Send feedback » Permalink


Permalink How can I raise lambs on irrigated pasture without having to use chemical wormers?

Answer: It is important to test for the amount and species of parasites that you may have on your pastures through fecal egg counts. Your veterinarian or your state veterinary diagnostic laboratory should be able to run these tests for you. Haemonchus contortus (Barber Pole Worm) is by far the predominant sheep parasite in the United States.

Successfully raising lambs on irrigated pasture while minimizing parasite infections can be accomplished through a three-pronged grazing-management approach:

1. Pasture rest period of 30 to 35 days
The rest, or pasture recovery, period is the time elapsed between the grazing of one paddock or pasture and its subsequent re-grazing. It is sometimes referred to as the grazing cycle time. On irrigated pastures in the dry Intermountain West, the infective larval populations of Barber Pole Worm tend to diminish after 30 days. Grazing periods that take advantage of this will limit the amount of parasite infection.

2. Paddock grazing periods of less than four days (one to two days is ideal)
The amount of time that livestock are in a particular paddock is the grazing period. The Barber Pole infective L3 larvae take four to five days to migrate out of a fresh fecal pellet and up the grass stem. Paddock grazing periods of less than four days minimize fresh ingestion of the L3 larvae.

3. Exit each paddock with a residual height of five to six inches
In general, most of the Barber Pole L3 larvae populate the first three inches of the grass stems. Leaving at least the bottom six inches of the grass plant intact when exiting paddocks results in less ingestion of the infective larvae. This practice also results in the trampling of residual grass, which will increase soil organic matter and soil fertility. This should be one of the primary objectives of any well-managed intensive-grazing system.

For more information on sustainable pasture management and parasite control, see the following ATTRA publications:

Integrated Parasite Management for Livestock

Managing Internal Parasites in Sheep and Goats

Tools for Managing Internal Parasites in Small Ruminants: Pasture Management

Why Intensive Grazing on Irrigated Pastures?

Irrigated Pastures: Setting Up an Intensive Grazing System That Works

Send feedback » Permalink


Permalink Can I use a cover crop of broccoli to limit Verticillium on my next crop?

Answer: The brassica family of crops can prevent certain diseases in crops, especially Rhizoctonia and Verticillium. All brassicas contain glucosinolates, which are believed to be effective against fungi and nematodes. Certain brassica plants are more effective than others, however, in the level of protection they offer. Plants with higher levels, such as Oriental and Idagold mustards, are believed to be the most effective.

According to Michigan State University's Department of Crop and Soil Sciences, brassica cover crops may reduce or suppress Verticillium in potato, and a host of other diseases and nematodes in various crops.

There is extensive information located in the E-Organics online article titled, "Brassicas and Mustards for Cover Cropping in Organic Farming." The following excerpt from this article summarizes some of the research on this topic to date. The full article is available at

"In Washington, a SARE-funded study of brassica green manures in potato cropping systems compared winter rape (Brassica napus) and white mustard (Sinapis alba) to no green manure, with and without herbicides and fungicides. The winter rape system had a greater proportion of Rhizoctonia-free tubers (64%) than the white mustard (27%) and no green manure (28%) treatments in the non-fumigated plots. There was less Verticillium wilt incidence with winter rape incorporation (7%) than with white mustard (21%) or no green manure incorporation (22%) in non-fumigated plots (Collins et al., 2006)."

While the brassica cover crop may help to reduce the incidence of Verticillium in the soil, it is advisable to take into account these other considerations when planting crops that are very susceptible to Verticillium. It is advisable to avoid planting your new crops where you had tomatoes or other Solanacea crops planted beforehand that are equally susceptible and often vector the disease many years beyond when they were planted (up to 10 years). Also, plant in an area with little weed pressure, as even Solanacea weeds can harbor Verticillium. Other common-sense preventive measures include planting in well-drained soil and using certified seed stock.

For more info on managing disease, see the ATTRA publication Sustainable Management of Soil-borne Plant Diseases, available at

Send feedback » Permalink


Permalink I want to use root-zone heating to grow cold-tolerant crops under floating row covers in my hoop house this winter. Is 16 inches too deep to run the tubing at 7,000-foot elevation?

Answer: Sixteen inches may be a bit deep for your situation as it may not provide effective root zone heating. It would be more effective to move the system closer to the root zone at 12 inches.

You could also install a thermal break (insulation) under the radiant tubing under each growing bed, and insulation around the perimeter of the tunnel. It may be possible to not use any energy inputs by doubling the layers of plastic on the tunnel with an air space between the layers. With the double plastic and plastic row covers inside the tunnel over each bed, you should be able to grow the right variety of crops over the winter with no energy inputs.

As a rough estimate, based on 750 Btu/hour/liner foot of radiant tubing, you need 270,000 Btu/day. Assuming an average of five sun hours a day in your location and a 24-square-foot collector, you need 11 panels and a 400-gallon solar storage tank. Again, these figures are for optimum production. You could start with fewer panels and a smaller tank and still get some benefit. The key will be to get the tubing close enough to the root zone to transfer heat to that area. If you could install a double layer of plastic with air blown between the layers, and use plastic instead of geotextile row cover cloths, you might be surprised at how well the right varieties of crops would do with no extra energy inputs.

For more information on season extension techniques for cold climates, see the ATTRA publication Specialty Crops for Cold Climates, available at

Send feedback » Permalink


Question of the Week Archives