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Home  > Question of the Week

Question of the Week



Permalink Can I plant figs in an unheated greenhouse in Zone 6?

Answer: The biggest variable in whether this endeavor will be successful is the duration of cold. For example, three fig growers in northwest Arkansas have had the same experience the last three years. They all achieved whole-plant survival and fruit in years 2012 and 2013, despite temperatures that once dipped down to -18 degrees F in 2012. However, it was -18 degrees F for only 12 to 24 hours, and that very cold temperature was preceded and followed by more temperate temperatures. However, this past winter, which dipped to zero only a couple of times, all of the three growers' figs were killed to the ground, including the cold-hardy Celeste, Brown Turkey, and Hardy Chicago cultivars (they're now re-sprouting from the roots). This is because temperatures stayed below freezing for a week or two several times.

The good news for you is that you do have a structure that should buffer the rate of temperature change and protect from desiccating wind. My best advice is to stick to the cultivars with the reputation for cold hardiness and be ready to supply supplemental heat from some source if it's going to get below 10 degrees F for extended periods. You might also consider some sort of framework that would allow you to drape tarps or blankets over the trees and provide some heat lamps or some other relatively safe source of heat for those coldest nights. It shouldn't take much to heat such a setup within the already wind-protected greenhouse. In fact, you'll need to be careful that temperatures inside such a structure don't get warm enough to predispose the tree to worse cold damage. You might also consider walling off some section of the greenhouse that you can dependably heat during the coldest periods—just enough to keep it above freezing, perhaps.

I wish I had better advice or word of some new miracle cultivar or invention that would make it easier, but at least I doubt that a fig in a greenhouse like you describe would ever freeze below ground—you should always at least get a breba crop.

For more information on fig resistance to cold, visit www.planetfig.com/articles/fareng2589.html.

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Permalink I've heard rainwater has a lower pH than municipal water. Would this be an advantage in a rainwater-collection system?

Answer: Rainwater starts out close to a neutral pH of 7. However, even the amounts of naturally occurring carbon dioxide (CO2) in the atmosphere lower the pH of rainwater. So rainwater has a natural pH of 5.4 to 5.7. With the increased amounts of manmade CO2 in the atmosphere, rainwater, especially in the industrial eastern United States, can have an even lower pH (referred to as acid rain). Rainwater can also pick up other pollutants like sulfur dioxide and nitrogen oxide as it falls. The amounts of contaminates and ranges of pH in your rainwater depend on location, but the rainwater you collect will almost certainly have a lower pH than the city-supplied water.

There is no definitive answer to the question of whether rainwater is better for the plants than city water. City water contains chlorine and sometimes fluoride. Chlorine will dissipate but may have an effect on soil microbes before it does, which would affect the nutrient availability to plants. Fluoride can build up in the soil and can be taken up by plants in small amounts. This last point is more of a concern about safe levels of fluoride for human consumption than about plant nutrient uptake.

Nutrient uptake in plants is mostly determined by organic matter content of the soil, microbial life in the soil, and the pH of the soil. Since acid rainwater can lower the pH and, in turn, the microbial life of the soil, it can have a negative effect on plant nutrient uptake. On the other hand, urban soils tend to have a high pH because of all the concrete used in urban development, so acid rainwater may help balance the pH of your urban soil. Also, rainwater may contain dissolved nitrogen that can help with increased nitrogen availability to plants. Good-quality handheld pH testers are available to take the guesswork out of soil pH. You can and should test your pH levels and adjust with lime for acid soils and with organic matter such as peat moss for a soil pH that is too high.

More important than the question of what type of water to irrigate with is whether you have enough water to irrigate with. Soil moisture is the biggest factor in plant nutrient uptake. If you irrigate with rainwater, do you have enough surface area and storage capacity to collect and store a sufficient amount to do the job? You can fix a pH problem, but if soil is too dry the microbial life shuts down, nutrients become immobile, plant roots die and plant growth stops. If you decide to go with a rainwater system, design and capacity is important, as well as a city water backup if it doesn't rain enough.

For more information, see ATTRA's Starting a Farm in the City at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=21.

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Permalink My soil was contaminated with an herbicide after I applied composted manure from animals that ate sprayed hay, and it’s stunting my crops. How can I remediate the contamination?

Answer: You’ll want to create conditions favorable to microbes (mostly fungi and bacteria) in order to break down the herbicide. The conditions that will favor microbes are moist and relatively warm, and perhaps diluting the contaminated organic matter with uncontaminated organic matter (“clean” leaves, grass clippings, and even manure). Also, keep the area well-aerated so the microbes have plenty of oxygen to thrive and break down the herbicide.

Another option is to apply several applications of compost tea (made from uncontaminated compost), and add some soil to help remediate the contaminated compost.

For more information, consult the following resources:

Notes on Compost Teas, ATTRA
https://attra.ncat.org/attra-pub/summaries/summary.php?pub=125.

Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings, North Carolina Cooperative Extension
www.ces.ncsu.edu/fletcher/programs/ncorganic/special-pubs/herbicide_carryover.pdf

Recommendations for Accelerated Remediation of Persistent Herbicides, Green Mountain Compost
www.greenmountaincompost.com/all-about-compost/compost-persistent-herbicides-fact-sheet/recommendations-for-accelerated-remediation-of-persistent-herbicides/

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Permalink What can you tell me about planning the basic infrastructure for small to mid-size vegetable operations, specifically for harvest/packing shelters, walk-in coolers, and washing facilities?

Answer: First, be mindful of the fact that the new Food Safety Modernization Act (FSMA) being written up by the FDA will have a lot of impact on your packing and storage facilities. The Act is not being enforced yet, but it soon will be. To learn more, visit http://www.fda.gov/Food/GuidanceRegulation/FSMA/ucm334114.htm. It is recommended that you really study this page and all the internal pages to which it directs you. These food safety regulations will limit some of the designs of packing sheds that used to be acceptable.

As far as sizing of each of the operations, e.g., the packing line, the wash tub, and the coolers, you need to think about how much product you will be harvesting and how long you intend to hold it on your property. Let's use the crop of summer squash as an example. Let's say your projected yield is about 1,000 boxes per acre, you will harvest that acre over a four-week period, and you will pick the crop twice per week. That means that you will harvest that acre of squash eight times, with an average harvest of 125 boxes. But remember you won't get harvests of 125 boxes each time. At the start (and finish), you will get less than 125 boxes per harvest. In the middle of the harvest, you will get much more than 125 boxes per pick. My experience with summer squash was that the third week of the harvest actually produced 40% of the total yield, so each of the harvests that week would deliver 200 boxes, for a total of 400 boxes that week. So your facilities have to be designed to process up to 200 boxes per shift even though the average harvest for that one acre is 125 boxes. As a rule of thumb, your packing line needs to be designed to run double the product flow from what you think your average will be.

Unless you also have the time and space and staff available to completely dry your produce after you wash it, I would not wash it in the first place. Back to the example of summer squash, unless the squash is really dirty when harvested it because it rained that day or the day before, it's a better approach to simply not get the squash wet. Boxing up squash that is not completely dry is a recipe for disaster. The product will have no shelf life. The same goes for tomatoes, cukes, peppers, melons, etc. Greens are an exception, as they are generally always washed.

Regarding sizing a walk-in cooler, the following webpage shows the correct storage temperatures for different fresh produce items: www.freshpoint.com/produce/handling_guide.html#. This is important as you don't want to store everything together in the same place at the same temperature just because items were harvested at the same time. In addition to questions about what products to store with each other (and what NOT to store with each other), you need to consider how long you think you will have to hold a given harvest. A cooler should probably be sized to hold one week's worth of production. If you hold a given harvest of something in your cooler for more than one week, chances are that it is not worth taking up that space in the cooler. Back to that acre of summer squash again, your weekly harvests over the four-week period will be 100 boxes, 300 boxes, 400 boxes, and then 200 boxes. Your sales will have to match up with that input flow as close as possible or you will be building up inventory in the cooler.

You could make the same calculations for one acre of whatever else you are harvesting, add all those boxes/week together to see how many boxes you probably will need to be storing. Each box you store will take up about 1.5 cubic feet of space. You don't want to store boxes on the ground in a refrigerated cooler, nor do you want to stack them all the way to the ceiling. You don't want to block air flow within the cooler. So if you had a cooler that was 8 feet tall, 20 feet long, and 15 feet wide and you stored boxes four inches off the floor and four inches from the top, you would have available approximately 2,200 cubic feet of storage. Dividing that by 1.5 and allowing for walking space, you could store about 1,300 to 1,400 boxes within that cooler, not considering issues of different temperatures needed for different crops.

For more information, see the ATTRA publication Postharvest Handling of Fruits and Vegetables, available at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=378.

Also refer to resources available from the Postharvest Technology Center, University of California http://postharvest.ucdavis.edu/.

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