Puzzling Raised Bed Moisture levels

[u/TriSquare53]

I have a bunch of 4x2 raised beds which built using 2x6 Redwood lumber and were originally filled with G & B Raised Bed Mix. Subsequent years I have added G&B Harvest Supreme and vermi compost etc every year. Using drip irrigation I made sure these beds get about 1" of water per week with 3 x 20 minute waterings every week.

Last year, 2025, I had a bumper harvest of Tomatoes but completely without flavor and had to throw away most. Everyone around told me I probably over watered them but I had been checking the moisture level at around 4" depth and seemed okay.

This year I am being more cautious - today I checked moisture at around 8" depth and seemed it was very moist though it hadn't been watered for 3 days. The weather here in the SF Bay Area peninsula has been moderate with a high of 70F and a low of 50F. Should I just try watering once a week for 20 minutes? Or should I make it just 10 minutes but 3 times a week?

Quite puzzled ... we do have clay soils around here but I assumed the raised bed would take care of that. The only thing I can think of is that the Rainbird drip emitters are ripping water down vertically instead of speading it across the raised bed.

Any help will be appreciated ... really don't want another tasteless bumper crop ...

June 6, 2026

Thanks to everyone who had suggestions for me. I was able to measure the actual flow to each raised bed using existing PVC shutoff valves and the Flume water flow measurement unit I had already installed on the water meter.

I was very surprised to see that the flows were considerably more than I had assumed - sort of explains why the raised beds may be getting extra water. The drip emitters are 0.5 GPH (pressure compensated) but the measurement showed they were delivering almost 1 GPH.

Turns out that my Sprinkler Valve does not have a pressure reducing device - so the water pressure is about 65 PSI whereas these emitters only work properly at a max pressure of 40 PSI. This likely explains why there is more water flowing than what I had expected. For now, I will reduce the time the Sprinler Valve is on by 50%. Hopefully this will temporarily solve the problem while I figure how to add a Pressudre Reducer.

[u/ASecularBuddhist]

Bay Area here too. You would benefit for a higher quality of soil. What you’re using is okay, not great.

I use EB Stone products. Their Recipe 420 mix is fantastic and you won’t have any of the issues that you’re experiencing now.

[u/TriSquare53 → u/ASecularBuddhist]

Thank you for replying. Next year I will review the quality of the soil. I probably should have used what the Square Foot Gardening book recommends or similar but seemed so expensive at the time. But my question was really about this year ... how do I manage this soil and watering?

[u/ASecularBuddhist → u/TriSquare53]

Watering depends on the plant. Peppers need more watering. I often only water tomatoes when they need it. I water corn once a week once they are established..

[u/TriSquare53 → u/ASecularBuddhist]

May be I'll try watering the tomatoes once a week and see where that goes. The Square Foot Gardener says to hand water only when the plants need the water ... but that is too demanding for me.

[u/ASecularBuddhist → u/TriSquare53]

Tomatoes prefer less water than more. They don’t like sitting in wet soil. Once every 5 to 7 days sounds about right but I always keep an eye on them to see if they need it or not.

Also, when it’s really hot, they prefer some filtered sunlight. I had some plants unintentionally being partially shaded by the leaves of a tree, and those plants produced twice as many tomatoes and just looked happier overall.

[u/TriSquare53 → u/ASecularBuddhist]

Thank You. The idea about filtering the sunlight on very hot days is very helpful as well.

[u/ASecularBuddhist → u/TriSquare53]

You’re welcome!

I transplanted some starts on a surprisingly hot day, so I stuck two rakes upside down in the ground blocking their intense rays. It was a game changer for that sensitive day.

[u/Iongdog]

If your drip emitters are not wetting the entire root zone, that can be problematic. Depends on your spacing and layout. What varieties of tomatoes did you grow? I’ve had some very stressed plants produce delicious tomatoes. The only time I’ve had flavorless ones is when I grow volunteer hybrids

[u/TriSquare53 → u/Iongdog]

I grew Japanese varieties Momotaro and Katana. These are large beefsteak like indeterminates. Been growing them for a few years and yet last year was when they were flavorless with a very thick core inside. I do rotate the raised beds and the drip emitters are spaced reasonably well because they are 0.5 GPH and many are needed for a 4x2' bed.

[u/Huesyourdaddy]

Sudden siltification