Sunnyvale Teaching and Demonstration Garden

Third Year, 2008

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Overview

The Sunnyvale Teaching and Demonstration Garden is located in a corner of the Charles Street Community Garden in Sunnyvale. The working team has included over 20 Master Gardeners, with 10 of us volunteering most weeks. The garden has four raised beds, two in-ground beds with California native plants for pollinator attraction, a blueberry hedge, a pot corral, and six other in-ground beds with a variety of edible plantings.

This year our projects included growing a variety of cool weather and warm weather vegetables, ornamental edibles, perennial vegetables, herbs, vegetables in containers, and cover cropping demonstrations. Several of our growing beds are in significant shade, which has enabled us to experiment with various crops to see what we can grow in the shade and demonstrate that for the public. Our trial of physical isolation as prevention for tomato russet mite was continued this year. We had russet mites in the garden and our isolation screen was not effective. The garden’s harvests were plentiful and allowed us to donate 25 pounds of fresh produce to the Charles St. Gardens' Food Forest/Sunnyvale Cares weekly produce collections and 78 pounds to Mountain View's Community Services Agency.
We presented nine talks to the public, including blueberry cultivation, seeding, garden infrastructure, harvesting, cover cropping and more. Two of these talks were in the nearby Sunnyvale Public Library. The talks in the garden were followed by "grand rounds" in the community garden, where we looked for successes and challenges in the garden beds with the class attendees. These rounds are always a favorite for everyone. We had 346 attendees at our 2008 talks.

Tomato Irrigation Trials – Dry-Farmed Tomatoes

The team at the Sunnyvale Teaching and Demonstration Garden (STDG) grew two “dry farmed” tomato plants in the Summer 2007 growing season. These plants were irrigated until the fruits reached approximately 1 to 1 1/2 inches in diameter. On June 26, 2007 the irrigation was turned off. The plants continued to grow and produce fruits whose taste was intense and almost unanimously preferred over the two sets (four plants total) of comparison treatments (watered weekly, watered twice weekly). The 2007 "experiment" was of such interest to the team, with the dry-farmed tomatoes tasting so much better than all the others, that we decided to repeat it in 2008 with the introduction of some scientific rigor. Our overall goal was to better understand just how much water is needed to produce excellent home-grown tomatoes. We wanted to be able to provide better answers to the public when asked how much to water. Aziz Baameur, a County Farm Advisor, advised us on our experiment, and recommended we involve of the water district.

Method

We planted tomatoes in three different locations and used three different irrigation methods:
1) weekly: regardless of need, the irrigation was run weekly
2) "as-needed": irrigated as needed based on tensiometer readings
3) "dry-farmed": irrigated as needed based on tensiometer reading until there was significant fruit set, at which time the irrigation was stopped for the remainder of the season.

We used Early Girl and Ed’s Millenium tomatoes, one of each in the weekly and as-needed groups, and two of each in the dry-farmed group. We also grew a Kellogg’s Breakfast in the dry-farmed group. We had a total of nine plants in our trial: two "weekly", two "as needed", and five "dry-farmed".

The Santa Clara Valley Water District provided nine tensiometers, which were installed in groups of three around three different tomato plants. Tensiometers give a measurement of moisture in the soil based on direct measurement of "soil suction." This is the force that plants have to overcome to get needed water (stated in centibars.) Each plant had a tensiometer measuring the soil at three different depths (12", 18", 24").

Execution

Tomatoes were planted on May 20, when nighttime temperatures were consistently above 50°. The tensiometers were installed the next day. Readings on all nine tensiometers were taken daily until July 15, when the measurement readings were stopped. By July 8 the fruit size of our dry-farmed tomatoes reached 1 to 1 1/2" in diameter so irrigation was stopped after that day. Until July 15 the other irrigation protocols were adhered to. Then, after July 15, the 'as needed' protocol was changed from relying on the tensiometers to relying on the gardeners to determine when to water, which was mostly every two weeks.

Working with the tensiometers
The tensiometers were read daily. The guidelines we were given indicated at what point we should irrigate. For the first three weeks, the readings indicated the soil was adequately moist. We were concerned about not watering the newly planted tomatoes but did not until the readings indicated that we should. Beginning in mid-June the readings began to indicate the need for irrigation much more frequently than we believed was necessary. For most of June we stuck to the plan, in spite of our reservations, which were backed up by the use of our hand-held moisture meters. In July the tensiometers led us to irrigate 11 of the first 14 days. We knew this was not necessary and decided, on July 15, to stop the readings. Our contact at the water district came out and checked and re-installed the tensiometers but the readings continued to be misleading in our opinion. They indicated the need for daily irrigation. We knew this was not true. We stopped the readings again on August 1.

Harvest and Taste
When we began harvesting fruits, we counted and weighed each method’s output. We also used a refractometer to get the Brix measurement, which indicates the sugar to water ratio of the solution measured. Higher Brix measurements correlated, for our group of tasters, to a better tasting tomato.

Sue Van Stee speaking to attendees at a talk in the garden.	Tensiometers installed around one tomato; each instrument goes to a different depth.	Using the refractometer to get a Brix measurement.

Outcomes

(see data table at end of report)

Dry-farmed tomatoes
These plants were smaller and less robust than any of the others. We concluded that the under-watering at the beginning of the season when we were relying on the tensiometer readings affected the health and size of the overall plants. The tomatoes were smaller with thick (sometimes tough) skin but with much sweeter and intense flavor.

Weekly irrigated plants
These plants were healthy and robust with good-sized fruits. The taste varied from bland, like a supermarket tomato, to respectable but unremarkable flavor.

As-needed irrigated plants
These plants were heavily watered during the early part of July. Consequently they were large plants with thick, lush foliage. The fruits ripened later and continued longer into the season. The taste varied from bland to very good; tomato fruit flavor seemed to improve as the plants received less irrigation.

Conclusions

We knew from the beginning that, as a scientific experiment, the design of our trial was definitely lacking. There were too many variables and too few samples (nine plants, two varieties, three irrigation methods.) We were using equipment whose results we didn’t believe almost from the beginning. In spite of all that we attempted to stick with the plan as long as possible.
In the end we did learn something about soil moisture, and continue to be interested in trying to come up with a way to better quantify "the right amount at the right time." We also confirmed, for the second year, that it is possible to grow delicious tomatoes with no irrigation after a certain point – at least in Sunnyvale.
Next year, we plan to irrigate tomatoes as we believe they should be – irrigate well to get the plants established, water only as needed until there is good fruit set, and then, if dry-farmed tomatoes are the goal, stop watering completely.
We have recommended that the water district work with the Nine Palms team where they have the space to conduct a more scientific trial.

Data from 2008 Tomato Irrigation Trial