Watering Container Trees

If you are growing figs in containers, it is absolutely critical that you water them correctly.  Any tree-sized plant, particularly one that produces fruit, must be watered carefully,  because it relies exclusively on the garden caretaker for all its water.  Overwater, and you're facing waterlogged roots and root rot.  Underwater, and your fig is in serious danger of drying out completely and possibly damaging the tree.

Soil must be moist for plant roots to take up nutrients

. Nutrients in the soil must dissolve in water to form a solution, which roots then absorb. Without sufficient moisture, nutrient uptake is impeded, reducing root growth and causing plants to starve or dehydrate. Excess watering, however, will quickly wash nutrients through the soil and out the bottom, causing a lack of growth and stagnant fruit development.

Watering starts with a well-draining soil, based on coconut coir, sphagnum moss, and perlite.  Including in your containers anything like garden soil or compost is a recipe for a muddy mess that promotes moldy roots and other disease. You also want to cover the soil and shallow roots with a layer of mulch, to prevent the sun from baking away the upper level of moisture.

The objective is to completely saturate your soil with water once a week.  Note that this doesn't mean flood your container and wash away your fertilizer.  You simply want to bring your water volume just to saturation, so that the growing medium is evenly moist throughout the column.  Then, you want to let the soil dry down over the succeeding days as the plant takes up water and nutrients.  Before it becomes too dry, you will water again, but again, only as much water as the plant needs.

Step One.  Check on the rainfall totals in your area.  To do this, go to Precip.ai and type in your zipcode to get started. Of particular interest is the record for Rainfall in the Last 7 Days.  You can also go to Weather.gov and check for rainfall for the last 72 hours/3 days. If it  hasn't rained in the last 3 days, you'll probably need to water your fruit trees in containers. Each of  these will give you an idea of how much watering your figs have received naturally.  

Figs generally need 1" to 1.5" of watering (rainfall or artificial) per week in the Summer to produce healthy fruit.  This can increase depending on the size of your tree and the number of fruits developing.  You should be watering more than once per week if there's no rain. The time to be careful about watering is during fruit ripening, but leading up to that, you can be more free with water.

Step Two.  Determine field capacity.  For this, we are going to need the garden hose.  Record the rainfall for the last 3 days and the last 7 days, using your resources above.  Now, use the hose in 3 second bursts to add water to your container.  Then pause at least 30 sec, to let the water work its way into the growing medium.  You are looking for the water to work its way entirely through the medium, until you see it eventually run out the bottom of the container.  

Work in 3 second bursts of water followed by 30 second intervals to allow the water to be absorbed.  Count the number of 3 second bursts, and when you observe the water running out the bottom holes of the container, record the number of bursts it required.  This will tell you how much water is required to fully irrigate that particular container.  For my 24" by 13" whiskey barrel, that could take 5 or more 3-sec bursts of water.

Step Three.  Repeat 3 days later.  Make a note of any rainfall accumulation in the past three days (Weather.gov) and average temperatures.  Then repeat the field capacity experiment, which will probably be smaller than your first trial.  What  you now know is that starting from saturation on Saturday, and with a known temperature and rainfall, how much watering it will take to bring the container up to field capacity again on Tuesday.  This is a rough gauge for how much you need to water and how frequently.

Again, remember that drawing down the water in the containers is key to avoiding mold and disease problems.  You never want to be completely dried out in the container.  If the Tuesday reading is the same as your initial field capacity test, then you know that your containers are drying out quickly, and so you must decrease your watering interval.  If, however, your container is quickly at capacity on re-wetting, then you know you probably need to stretch the interval between waterings to a few more days. 

   

Persephone

The Persephone period is the time of year when growing light hours fall below 10.  It is named for the time of year when the Greek goddess Persephone visits the underworld and her mother Demeter is stricken with grief.   

Below 10 hours of growing daylight, plants generally become dormant and cannot put on new growth or produce fruits or flowers.  This is true, regardless of the ambient temperature.  For example, even in a greenhouse where the temperatures are regulated, in the dark of winter, plants generally do not grow during the Persephone period without supplemental light.

 

In Virginia: 

On October 11th, sunrise is 7:25 am and sunset is 6:25 pm for a total daylength of approximately 11 hours.  

The threshold of 10 hour days is typically when plants stop growing and developing.  On October 31st, daylength is approximately 10 hours.  Actual daylight hours, including twilight, is about an hour longer.     

On December 21, day length is 8:23 hours long in Virginia, the shortest day of the year.  On February 10th, daylength again crosses the 10 hour threshold when the most cold-hardy plants begin growing again.

Note that this is different from temperature patterns, where February is typically the month of the year with the greatest potential for winter snow. 

 

Greenhouse Modifications

 OK, so you've got your greenhouse kit waiting to be assembled.  What follows are a few modifications that will improve the experience, recommended by gardeners who have lived with and experimented with their greenhouses over a few seasons.

 

Modifications #1 

1.  Use some kind of treatment on the lower wooden panels.  These are the panels that will see the most wear from rain, dust, mud abrasion.  Even if the wood is already cedar or pressure treated,, use some kind of weathering treatment to extend the life of the whole greenhouse.  Water seal, polyurethane, whatever you can get by the gallon.

2.  Ventilation is key in the summer.  The inside of the greenhouse will become an oven if the doors and windows remain closed.  Make sure that all ventilation remains open and unobstructed.  Find a way to secure doors open.  Are there temperature regulated windows or louvered vents that can be used in shoulder seasons to regulate the temperature?  This is key in June when the nights would benefit from the greenhouse being shut, but daytime temps can spike to dangerous levels when the sun is beating down.  

3.  Strategies for the height of summer - July and August.  

• Consider covering with shade cloth at the hottest months.  Even partial covering, of the back half for example, can give you some escape from the intensity.
• Find ways to open as many panels as possible.  
• Put some of the lower panels on hinges to fully open but add cabinet hardware to seal securely in the winter.  
• Add additional screened vents that can be closed or sealed with plastic in the winter, but will pull more air into the interior in the summer.  

 4.  Interior plumbing.  

• Add a hose bib, 
• draining into a basin inside to rinse off vegetables and water seedling trays.  
• Supply water with a garden hose on the outside, but use actual plumbing on the inside.  
• Consider a  rain barrel collection system off the roof 

 

5.  Electricity for working in the evenings during the fall and spring.  Use a heavy duty extension cord to run temporary power to the greenhouse.

• Overhead lights 
• Ventilation fans
• Diesel heater
• 
  

6. Heat.  What can be done to keep the interior above freezing overnight:

7. Lighting.  

• Overhead lights 
• seed starting lights
• Solar exterior lights. 

8.  Wire frame shelves for seed trays 

9.  Plant some flowering around the greenhouse, and even inside to attract pollinators.

10.  For deep winter cold,  plan for layers of frost protection.  

• Seal the gaps in the outside envelope of the greenhouse. Use a clear silicone to calk the seams.
• Consider adding bubble wrap on the roof, or reflectix around the solid perimeter walls for extra insulation.
• Create a smaller area within the greenhouse by enclosing it with plastic sheeting.  This could be a tent within the greenhouse, or section off one bench or one wire shelving unit.  Make bags out of agricultural fabric with a draw string around the opening that you can pull tight over individual pots.
• Within these small microclimates, you can introduce smaller, more efficient elements of heat, such as a seed-starting heat mat, or C7 string lights that can heat a much smaller area without a heavy electrical demand.
• Place water barrels within the zones to add thermal stability.  They absorb heat during the day and radiate it again at night time when outside temperatures are the lowest 
• Create "propagators" out of clear plastic tubs that will hold a seed starting flat or 10x20 tray. Place a heat mat in the bottom as a heat source.
• The use of a space heater with the thermostat set to a minimal 40 F can be effective to keep plants from freezing without being excessively expensive.  This will not produce tomatoes in January, but it may allow some already cold hardy winter greens from pushing through an outside freeze.