Posts Tagged ‘transplanting’

Plasticulture Troubleshooting

Friday, April 25th, 2008

Gordon Johnson, Extension Ag Agent, Kent Co.; and Tracy Wootten, Extension Horticulture Agent, Sussex Co.

There is a large acreage of vegetables grown using plasticulture in Delaware. The following are some common problems that we often encounter with vegetables grown on plastic mulch.

Fertilizer Damage
There are several ways that fertilizers can injure plants grown on plastic. The most common problem is salt injury. In bed forming and plastic laying operations, caution must be used when using banded applications of fertilizers. Fertilizer banding attachments on plastic layers should be set well to the side of where the plant row will be (>6 inches). Bands too close to where plants are set may lead to salt injury. It is better to distribute the fertilizer over the area to be covered and incorporate it 4-6″ before bedding and laying plastic. Some growers use dilute fertilizer solutions with the plant water. Care must be taken to keep the salt levels low (less than 1% solution is safe – see the specific label recommendations for the fertilizer product being used). Ammonia volatilization and toxicity can be a problem with use of urea or high ammonium containing nitrogen fertilizers under plastic. At least 50% of the nitrogen source should be in nitrate form.

pH Issues
We often see problems with low pH in plastic beds. In cantaloupes, this has led to manganese toxicity in the past. Make sure that the soil pH is corrected by liming well ahead of laying plastic. Remember that pH will drop some with the use of ammonium nitrogen fertilizer sources under the plastic and soils with a marginal pH (around 5.8 for example) can drop down to levels that will affect plant growth (5.3 or lower).

Transplants With Small Root Balls
A common problem we see is the use of plants with inadequate root balls that are then susceptible to wilting and desiccation with high winds, especially during cold snaps.

Planting Depth
Poor plant performance or plant loss can result from setting plants too deep, especially with smaller plants where the soil covers growing points and from setting plants too shallow where part of the root ball is exposed, causing plant desiccation.

Excessive Transplant Shock
Plant loss often occurs by allowing plants to dry out too much prior to setting (sitting long periods in the wind on wagons for example), by allowing plant trays to heat up too much in the sun, or by planting into black plastic on very hot sunny days.

Heat Necrosis
As black plastic heats up, the temperature right around the plant hole can get so hot that it will kill the plant tissue nearby, right at the soil line, causing the plant to die. This occurs most often where plant stems touch the plastic mulch and with plants that have small stem diameters.

Improper and/or Malfunctioning Drip Irrigation
Vegetables grown on plastic mulch require more attention to providing proper irrigation. Common problems include under-watering (keeping beds too dry), over-watering (leaching out plant nutrients), plugged drip emitters causing dry spots, holes in drip tape causing wet areas at the leak and a under-watered bed beyond the leak, and pressure losses resulting in drip tape not operating properly and giving poor water distribution.

Cold Effects on Early Transplanted Vegetables

Friday, April 18th, 2008

Gordon Johnson, Extension Ag Agent, Kent Co.;

The frost we had this week should remind growers that as you try to get a jump on the growing season, cold weather effects need to be considered. Over the years, many of our early plantings of summer vegetables have suffered because of early cold damage and inadequate provisions to protect plants.

There has been a tendency to risk earlier and earlier plantings as growers try to hit the early market.

Earliest plantings of watermelons, cantaloupes, summer squash, and tomatoes will begin in the next 10 days. First transplanting of crops such as peppers and eggplant will begin in early May. One of the characteristics that all of these crops have in common is that they are warm season vegetables that are sensitive to cold temperatures, both in the root zone and above ground.

Considerations for early transplanted warm season vegetables:

1. Choose the lightest ground that warms up quickly for early plantings. Plant higher sections in the field first. Avoid areas that receive any shade from woods or hedgerows. Early fields should be protected from extreme wind and should not have frost pockets.

2. Lay plastic mulch well ahead of time to warm soils. Black plastic mulch should have excellent soil contact. Loose mulch is much less effective in warming soils.

3. Consider using IR plastics that trap heat (green and brown plastics). Clear plastics can be used but weeds are an issue and a good herbicide program will be needed

4. Make sure that there is good soil moisture when forming beds and laying plastic because soil water will serve as the heat reservoir during cold nights.

5. Careful attention needs to be paid to hardening off warm season vegetable transplants that will be planted early. Gradual acclimation to colder temperatures will reduce transplant shock. Do not transplant tender, leggy plants or plants coming directly out of warm greenhouse conditions for these early plantings.

6. Use vegetative windbreaks such as rye. This will reduce heat transfer by wind. Consider using windbreaks between each plastic bed in early plantings.

7. Consider using covers to protect from cold and wind and to increase accumulated heat. This includes slitted and perforated row covers and floating row covers.

8. Watch extended weather forecasts and plant at the beginning of a predicted warming trend.

9. Monitor soil temperatures in plastic beds and do not plant if they are below 60°F. Soil temperature in beds should be measured at the beginning of the day when at the coolest. When soil temperature conditions are not favorable, wait to plant.

10. Avoid planting in extended cloudy periods, especially if plants have come out of the greenhouse after an overcast period. These plants will not perform well.

11. When transplanting, make sure that there is good root to soil contact and there are few air pockets around roots.

Transplanted warm season vegetables vary in their ability to tolerate adverse weather after being set out. Tomatoes will stop growth but will grow out without much damage once warm weather returns. Summer squash also handles adverse conditions fairly well. Watermelons will hold if they have been hardened off properly. Cantaloupes can be permanently stunted if exposed to excessively harsh early conditions. Peppers and eggplants will not put on any root growth until temperatures are warm enough. Remember that all of these vegetables are susceptible to frost damage and will be killed by a late freeze.

In years with cold, cloudy, windy weather after transplanting, we have had large losses of transplants in the field. In many fields considerable hand labor was used to replace dying plants and in some cases whole fields were replanted. It is critical to have warm soil conditions after transplanting to allow roots to grow out into the bed quickly. What happens in cold, cloudy conditions is that plants shut down physiologically. Little root growth occurs and the existing roots on the transplant do not function well. If there is any wind, plants lose more water than they can take up and they die due to desiccation. This is accelerated when the sun does come out – the first sunny day after an extended cold, cloudy period is when you will see the most wilting of weakened transplants.

Later on in the growth cycle, cold weather during flowering can lead to problems with pollination and fruit formation resulting in reduced fruit set and malformed fruits.