Posts Tagged ‘plasticulture’

Continuing Vegetable Sales in Fall and Winter

Friday, September 21st, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

While most vegetable growers finish up with fall crops around Thanksgiving, there is potential to produce throughout the fall and winter. There are fall and winter sales potentials with schools, institutions, and restaurants; for CSA’s; and for specialty wholesale markets.

One strategy is using storage to have products available out of season. This has been a common practice on a large wholesale scale with potatoes and apples where large controlled environment storage facilities are used. On a smaller scale, there are many vegetables that can be stored in sheds, cold boxes, or greenhouses as long as products are kept above freezing and have adequate humidity. It should be noted that critical minimum temperatures will vary according to the type of produce.

Probably the easiest vegetables to store are hard shelled winter squash such as butternuts. If kept around 50°F, most of the hard shelled squashes can be kept for at least 3 months, some for over 6 months. Potatoes store best at 45°F in high humidity and sprouting can be a problem for longer storage. Sweet potatoes, once cured, can be stored for months as long as the storage temperature is kept around 60°F. Colder temperatures damage the roots. Onion storage depends on the type but longest storage is just above freezing in dry conditions. Cabbage can also be stored for long periods. The key is to grow storage varieties that are dense. Longest storage is at 32 F° in high humidity. Napa type chinese cabbage also stores well in refrigeration (several months). Other crops successfully stored include carrots, parsnips, rutabegas, and turnips. In fruits, long keeping apple varieties can be stored for months in cool temperatures.

Field storage is another way to extend sales of some vegetables. Root crops such as carrots, parsnips, and beets can be kept for extended periods in the field if kept from freezing with row covers or straw mulch. Certain cabbage varieties can field store into winter if protected from hard freezes with row covers. Green onions and leeks also field store well.

An alternative strategy is to make used of high tunnels, low tunnels, row covers, or a combination to grow cool season crops for fall and winter harvest. Greens crops in the mustard family (mustard, turnip, kale, collard, cress, many asian greens); spinach, chard, and beet greens; and lettuces and endive can be planted in the late summer or fall and harvested repeatedly through the fall and winter in these protected systems without additional heat. Some day neutral strawberries can be harvested into the late fall in high tunnels or low tunnel/row cover systems. The use of row covers can also extend harvest periods for crops such as broccoli where side shoot production can be maintained after main heads are harvested, often through Christmas, and Brussels sprouts where sprout production can be extended into winter.

Of course, there is potential for production of many crops in heated greenhouses. The choice of varieties becomes important for greenhouse production because of the lower light and reduced daylength conditions in fall and winter. Specific greenhouse varieties of crops such as tomatoes, lettuce, and cucumbers have been developed for fall and winter production.

High Tight Beds for Plasticulture Strawberries

Friday, August 31st, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Highest yields in plasticulture strawberries require proper bed formation. While bed makers and plastic layers used for vegetables can be used, it is preferred to use bed makers specifically designed for plasticulture strawberry systems (such as a Kennco or Reddick machines). These produce beds that are 32 inches wide at the base, 30 inches wide at the top and 10 inches tall with a crowned top for good drainage. With this type of bed, you can have bed centers at 5 ft between beds. It is also important to lay the plastic so that it is tight against the soil. This allows for effective heat transfer that will promote good strawberry growth in the fall.

When to Plant Plasticulture Strawberries

Friday, August 10th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

In 2011, the common observation was that later planted Chandler strawberries out-yielded earlier plantings. This illustrates the dramatic effects that fall and winter temperatures can have on plasticulture production.

Chandler has been our main plasticulture berry and has shown consistently high yields. For most of Delaware, the recommendation has been to plant Chandler the second week in September. In conversations with Dr. Barclay Poling, who is the recognized expert in plasticulture production in North Carolina, he stated that Chandler is more sensitive to fall and winter temperatures than other varieties and in warmer conditions Chandler will put on too much growth, leading to small berries the following spring; therefore, knowing when to plant is difficult. If you could accurately predict fall and winter temperatures, you could adjust planting dates, but of course this is not possible.

One strategy has been to make multiple plantings of Chandler one week apart starting the second week in September. This will insure that a part of the crop will come out of winter with the proper number of crowns (not too many, not too little). Unfortunately, this means that part of the crop will be low yield and part will have small berries.

Another strategy is to switch to varieties that are less susceptible to putting on too much growth. This is where the variety Camarosa may have a fit, as it is less temperature sensitive than Chandler in the fall and is not prone to putting on excessive growth. Camarosa is however sensitive to high April temperatures which can halt flowering in the spring, but in normal years will extend the season better than Chandler.

Sweet Charlie, the early berry that also can put on a second late crop, is normally planted 7-10 days ahead of Chandler. It is not an option to replace Chandler. For other varieties being tried, such as Festival and Bish, we still do not have enough research in our region to know if they can be replacements for Chandler.

Another strawberry that should be considered by growers is Albion, a day-neutral variety. It too is not sensitive to when it is planted in the fall. While much less productive in the main Chandler season, it has some unique properties that make it valuable to growers. First, it will give some early production, ahead of Chandler. Second, even though production is lower, it produces evenly over an extended period of time from April through early July. In general it will give 5-6 weeks more production than Chandler. It is a large, firm berry, that, while not as sweet early in the season, has good quality in May and June. Because plants are smaller and there are fewer berries per plant, it should be planted at a higher density than Chandler.

Low pH in Plastic Mulched Beds

Friday, July 20th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Each year we see problems with vegetable crops related to low pH in plastic mulched beds. A common scenario is a field with sandy soil (loamy sand, sandy loam) that has not been limed in the last 2 years. The starting pH of beds in this situation will usually be 5.5-6.0. Granular or liquid nitrogen fertilizers applied prior to or at bed formation and nitrogen fertilizers applied through the drip irrigation system during fertigation will commonly consist of ammonium sulfate, urea, ammonium nitrate or UAN (urea-ammonium nitrate) solutions. All of these fertilizers are acidifying because the ammonium which they contain (urea releases ammonium nitrogen as it reacts with the soil). Ammonium will convert to nitrate in the soil, a process called nitrification, and will release hydrogen (H+) ions, thus dropping the pH. As a result, pH in the plastic mulched beds gets progressively lower throughout the growing season. Beds with a starting pH of 5.5 can drop down into the 4s. The largest drops in pH will be in the wetted area around the drip emitter and drier areas of the bed will have a higher pH.

As pH drops, availability of magnesium and calcium declines while manganese availability increases, often to toxic levels. Below pH of 5.2, the chemistry of the soil changes and aluminum is released into the soil solution at increasing levels, further acidifying the soil. This free aluminum also is very harmful to plant roots because aluminum interferes with calcium, can bind with phosphorus, and can interfere with cell expansion at root tips, effectively stopping root tip development. Most of the active mineral nutrient uptake occurs in the region just behind the root tips. Without further root tip growth, nutrient uptake will become limited. Effective rooting volume is also reduced, thus placing the plant under additional stress. In severe cases, plants can die.

Managing plastic mulched bed pH starts with making sure that fields are limed the fall before beds are to be made. Spring applications can also be made to the area but full lime reaction should not be expected. Manage fertilizer programs so that large pH drops do not occur. This means switching some or all of the nitrogen program to nitrate sources – calcium nitrate and potassium nitrate would be examples.

If marginal pHs are encountered after plastic is laid (below 5.8), consideration should be given to eliminating ammonium or urea containing fertilizers and switching to calcium nitrate and potassium nitrate sources for fertigation. Both these fertilizers cause a basic reaction in soils because plant roots excrete hydroxides and carbonates as they take up the nitrate. There are few other materials that can be used to raise the soil pH through the drip system once plastic is laid. One option is potassium carbonate which is alkaline and thus will raise the pH. It is fully soluble and can be made in liquid forms. Liquid lime products with ultrafine ground limestone can also go through a drip system; however, getting enough material into the soil to affect the pH will be difficult and expensive and agitation of supply tanks will be necessary.

Day Neutral Strawberry Production

Friday, June 1st, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Strawberry season started early this year and is now winding down. The heat over the holiday weekend has essentially shut down additional flowering and fruiting in our spring bearing varieties so expect limited production into June. The critical high temperature for strawberries varies but any temperatures in the high 80s or 90s will reduce or stop flowering altogether.

There has been significant interest in the use of repeat blooming strawberries for extended production. These “day neutral” varieties can provide good spring production with continued production into the summer and fall, depending on the planting date. Day neutral strawberries are different from spring bearing types because they are not triggered to flower by daylength and can flower and fruit repeatedly as long as temperatures are suitable. Day neutrals vary in their ability to flower during the summer, and have been classified as either weak or strong. Strong day neutrals produce flowers and runner sparsely during the summer, flowers form on runners, and plants tend to be small with a moderate number of crowns. Intermediate and weak day neutrals, have more of the spring bearing characteristics, such as a stronger tendency to runner in summer. We recommend strong day neutrals for summer and fall production in our area.

In the past, the day neutral varieties Tribute and Tristar were used in this region; however, berry size is small. Certain day neutral varieties bred for use in other regions (California and Northern Europe) have been successfully used in this region and have larger berry size and higher yields, Seascape, Evie 2 and Evie 3 for example. Unfortunately these varieties have soft berries. Albion has shown good promise as a day neutral with large firm berries, small plants, and long term, even production and low disease pressure. It is lower yielding than others but works well in our region. Other California bred day neutral varieties such as Monterey and Portola have shown promise for our area. The USDA breeding program in Beltsville, MD is currently selecting day neutral varieties that would be better adapted to our region.

Day neutrals can be planted in the spring for summer, fall and carryover spring production; planted in summer for fall and carry over spring production; and planted in fall for spring, summer and fall production the next year.

For summer production with day neutral varieties, the use of aluminized reflective plastic mulch with drip irrigation is recommended. Additional provision for heat abatement will be necessary. This may include low volume misters for evaporative cooling during hot daytime temperatures or the use of white or reflective shade cloth. Drip irrigation should be run during the day to further limit bed heating.

Remove runners from all plants throughout the season. Runnering decreases markedly after fruiting begins, so while this task is somewhat intensive early in the season, it becomes insignificant later.

Flowers should be removed for 6 weeks following planting to allow the plants to achieve sufficient size for fruiting. Failure to remove flowers will result in small plants and low yields. Extending the period of flower removal beyond 6 weeks will result in larger plants, berries and second-year yield, but less production in the first year. Varying the flower removal period will not affect the timing of production peaks.

Day neutrals benefit from a continuous supply of nitrogen and potassium. Additional phosphorus is not necessary provided an adequate supply has been incorporated before planting. Apply 5 to 6 lbs/A of nitrogen through the drip irrigation system every week. Calcium nitrate is the preferred source of nitrogen early in the season, UAN solution can be substituted when temperatures warm. Supplement preplant potassium with 10 lb/A of K2O at monthly intervals, or 2 lb/A at weekly intervals through the drip irrigation system during the growing season. Day neutrals tend to be heavy consumers of boron because of their large commitment to reproduction. Monitor leaves occasionally to ensure that boron levels do not fall below 30 ppm. An application of 2 lb/A Solubor may be required in midsummer if boron levels are too low.

Gray mold is the biggest disease problem of day neutral strawberries. Because berries are continuously present, mold inoculum tends to increase during the season. Remove moldy berries from the planting, and protect flowers every 10 days to 2 weeks with an application of fungicide, especially after rainy periods.

To extend production in the fall floating row covers, clear row covers, or a combination can be used to conserve heat. If fall production is to be targeted, mid-summer plantings on black plastic mulch would be recommended but overhead irrigation is essential for establishment.

Day neutral plantings can be carried over to a second year. Plants should be cut back and crown thinning may be necessary in some varieties.

Some information in this article was taken from this factsheet: http://www.omafra.gov.on.ca/english/crops/facts/89-099.htm

Plastic Mulch Beds and Dry Soils

Thursday, April 19th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Due to dry weather, a significant amount of plastic mulch has been laid this year in dry soils and in soils with more clods than normal. This can be problematic for a number of reasons. The first is related to bed heating. For effective heat transfer, plastic mulch should be laid tight on a firm bed and the soil should be moist. Moisture is also critical for heat accumulation, because water absorbs more heat than soil minerals. In dry and cloddy soils much of the heating benefit of the mulch is lost. Root growth will be slowed and crops will be delayed. Another issue is water movement in the bed. Clods create large air spaces that limit capillary water movement thus reducing how much of the bed that can be wetted during an irrigation event as drip irrigation is started.

With rain forecast for this weekend, soil conditions should improve for plastic laying. Where overhead irrigation is available, irrigating soils prior to working ground and laying plastic is also an option in dry conditions.

Updated Fertilization Recommendations for Drip Irrigated Crops

Thursday, April 19th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Extension specialists in the Mid-Atlantic have updated fertilizer recommendations for drip irrigated plasticulture production of crops in the Commercial Vegetable Production Recommendations. The following are recommendations for watermelons and tomatoes.

Suggested Fertilizer Program Using Trickle Irrigation for Watermelons

Days After Planting

Daily

Cumulative

Nitrogen1

Potash1,2

Nitrogen1

Potash1,2

——————–lbs/A——————–

Preplant3

25

50

0-14

1.0

1.0

39

64

15-28

1.5

1.5

60

85

29-56

2.0

2.0

116

141

57-78

1.5

1.5

137

166

79-93

1.0

1.0

150

175

1Adjust rates accordingly if you apply more or less preplant nitrogen and potash.
2Base overall application rate on soil test recommendations.
3Applied under plastic mulch to effective bed area using modified broadcast method. Adjust as needed.
Note: recommendations are based on 8 foot bed centers. If beds are narrower, fertilizer rates per acre should be adjusted proportionally. Drive rows should not be used in acreage calculations.

Suggested Fertigation Schedule – Fresh Market Tomatoes

Days After Planting

Daily

Cumulative

Nitrogen1

Potash1,2

Nitrogen1

Potash1,2

——————–lbs/A——————–

Preplant3

50

125

0-14

0.5

0.5

57

132

15-28

0.7

0.7

67

142

29-42

1.0

1.0

81

156

43-56

1.5

1.5

102

177

57-77

2.2

2.2

148

223

78-98

2.5

2.5

201

276

1Adjust rates accordingly if you apply more or less preplant nitrogen and potash.
2Base overall application rate on soil test recommendations.
3Applied under plastic mulch to effective bed area using modified broadcast method. Adjust as needed.
Note: recommendations are based on 6 foot bed centers. If beds are narrower, fertilizer rates per acre should be adjusted proportionally. Drive rows should not be used in acreage calculations.

Additional recommendations can be found in the Recommendation which is also online at this site: http://ag.udel.edu/extension/vegprogram/publications.htm.

Monitoring Nutrient Levels for Plasticulture Strawberry Production

Thursday, April 5th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

In last week’s Weekly Crop Update, I gave some recommendations for petiole sap nitrate and potassium levels in plasticulture strawberries. This is based on sampling leaf petioles from the most recently expanded leaves from plants in the field, extracting the sap, and using portable nitrate and potassium meters. The procedure can be found at this website http://edis.ifas.ufl.edu/cv004, along with recommended levels for different growth stages.

While this is a quick way to monitor nutrient levels, growers are also encouraged to take petiole and leaf samples for laboratory analysis. The recommended levels for petiole nitrate and leaf tissue contents from laboratory analyses can be found at this publication from North Carolina: http://www.ncagr.gov/agronomi/pdffiles/sberrypta.pdf. A description of how to sample is also given. We do now have a lab on Delmarva that can run tissue samples. Leaf tissue nitrogen levels should be maintained as follows: N (%) 3–4, P (%) 0.2–0.4, K (%) 1.1–2.5, Ca (%) 0.5–1.5, Mg (%) 0.25–0.45. Petiole nitrate content until the end of the month should be around 4000 ppm (3000 ppm is low and 5000 ppm is high).

Avoiding Failures with Early Planted Vegetables

Thursday, April 5th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

The mild weather has many growers eager to get an early start with summer vegetables. Early markets are often the most profitable with higher prices. However, growers should proceed with caution and realize that failures can occur if cold sensitive vegetables are planted when temperatures are sub-optimal. As we get back to more seasonable weather in April, there will be many nights ahead with temperatures in the 30s and frosts and freezes are still a concern.

Each vegetable crop has a minimal temperature at which growth will occur. Our summer vegetables such as tomatoes, peppers, cucumbers, watermelons, and squash simply do not grow if temperatures are in the 40s or 50s. Squash and cucumbers do not put on growth with temperatures below 60°F, cantaloupes, watermelons, tomatoes, peppers, and eggplants will not put on growth with temperatures below 65°F. If temperatures are below these minimums, plants will just “sit still” and will be at risk of cold injury, wind injury, and damage from early season insects and diseases. Cold soils will limit root growth, further placing plants at risk due to inadequate water uptake and the risk of desiccation. Excess cold can also stunt some summer vegetables so that they do not fully recover. This is especially true of cantaloupes.

When planting summer vegetables early, growers need to consider all the tools available to maximize heat accumulation and minimize heat loss. The following is a list of these tools:

  • · Use raised beds or ridges. Ridges that are oriented east-west with crops planted on the south side, will benefit from the additional heat accumulation from the increased solar radiation on that side. Sandy soils heat up quicker due to lower water content.
  • · Use planted windbreaks, most commonly rye, between beds or rows. Windbreaks reduce heat loss from cold winds and help to accumulate heat. Rye reaches full height by the end of April on most of Delmarva. Cold winds are the most damaging to summer crops. Sand blasting during dry wind storms can actually cut plants off at the soil level. Growers doing field plantings for early crops in unprotected areas should always use windbreaks.
  • · For direct seeded crops, choose cold tolerant varieties, plant shallower and into well drained soils, and choose protected fields for earliest plantings. Also till soils well ahead of plantings to allow for them to heat up. Plant as soon as soil temperatures are adequate for germination. Also choose seed that has high quality and performs well in a cold germination test.
  • · To warm the soil more quickly, use plastic mulches. Plastic mulches increase soil temperature and help hold heat during night periods. They can increase soil temperatures 5-20 F° depending on mulch color. In order of lowest to highest heat accumulation Black < Red < Blue < Olive/Brown < Clear in selecting mulches. Mulches should be laid tight on a firm moist bed that is clod free. This will allow for more effective heat transfer and accumulation. Loose plastic and cloddy soils will reduce plastic mulch benefits.
  • · Use clear poly plastic covers. Most commonly, these come with slits or perforations to vent excess heat. They can be placed over direct seeded or transplanted crops with wire hoop supports (low tunnels) or they can be placed over ridges with transplants or seeds planted in the depression between the ridges. Zip tunnels and vented systems, where clear plastic can be easily closed and opened, have also been used. High tunnels also use poly plastic for protection and heat accumulation. I will discuss high tunnel management further in additional articles.
  • · Use spun bond poly or woven poly floating row covers to insulate, frost protect, reduce wind, reduce heat loss from soils and beds, and accumulate some heat. They can be placed directly over low growing crops such as strawberries or can be used with wire supports for other crops. The insulation they provide can protect 2-8 F° depending on thickness. Usually a 0.9-1.2 oz. cover is used to provide protection but not limit light too much.
  • · For smaller plantings, use of additional heat sinks to absorb heat during the day and then release it at night can promote earliness. Heat collection devices are usually filled with water and may be clear or black plastic containers or tubes.

Combinations of these practices will provide greater cold protection, heat accumulation, and earliness. This could include plastic mulch + row cover, plastic mulch + clear row cover + floating row cover, plastic mulch + row cover + heat sink, plastic mulch + clear row cover + floating row cover + heat sink. Use of these combinations in a high tunnel will further enhance success with early planted summer vegetables.

Plasticulture Strawberry Fertilization

Thursday, March 29th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Plasticulture strawberries should have had nitrogen applications already, prior to bloom. Addition of 3-5 lbs of nitrogen per acre per week may be warranted. Nitrogen is critical prior to and during early bloom. Including potassium at a 1:1 or 1:2 ratio with nitrogen will often improve fruit quality (sugars). Use of tissue testing throughout the strawberry season is recommended to monitor nitrogen and potassium levels. Targets are 500 ppm petiole sap nitrate and 2500 ppm petiole sap potassium. Additional calcium may be needed as the season progresses.