Watering Veggies on a Dripline


#1

I’ve set up my zone schedules but I’m concerned about my vegetable garden. I don’t see any listing for “Vegetables” so I’ve selected “Perennial” as the vegetation. I also selected “Loam” for the soil, “Lots of sun” for the exposure, and “Flat” for the slope. I also input a custom nozzle. This resulted in a watering time of 1 hour 23 minutes. That’s about half of what I used to water, and the plants are looking mighty thirsty. Has anyone nailed their settings for a raised bed vegetable garden that would care to share their info?

In case it would help get an accurate recommendation, here are my specs: My vegetable garden is made up of three 4’ x 8’ raised beds. I’ve got Netafim drip line installed in these beds, which have built-in emitters every 18", and the lateral lines are 18" apart. The Netafim label specifies these emitters deliver water at .92 GPH. I found a gallons per hour to Inches per hour convertor online which gave me a figure of “.66” to put in the “Precip” area. This resulted in a 1 hour 23 minute watering time about twice a week. Our temps hover in the mid 90s to lower 100s most of the summer. Does my Flex schedule sound about right? Should I just relax and let it do it’s thing?


#2

Your settings sounds similar to what I used for my raised bed last summer when I was trying Flex daily to irrigate it. If you’re expecting deeper watering you might look at the root depth setting. Increasing it will increase the runtime, but also spread apart the intervals. To increase the amount of water you deliver without changing the interval, drop your custom nozzle precipitation rate.

I’m surprised that you’re doing OK with twice a week. I was at every day here in the desert, but our temps were higher and maybe drier air. I eventually moved to a fixed schedule for my pots and veggie garden, based on a recommendation by a resident expert here, @sunny. In my case I needed to water more than once a day and Flex daily is limited to watering only once daily. If you’re interested in reading more, check out Dante’s Garden.

If you decide to play around with Flex some more, take a look at this article. The ‘Zone Attribute’ table about midway down is particularly helpful.


#3

For planters, I use dripline with embedded drippers at 6" spacing that’s rated at 0.52 GPH. I set a precipitation rate of about 0.6" per hour. This basically assumes about an 8" radius wetting circle since 0.52 gallons is ~120 cubic inches and an 8" radius circle is ~200 square inches. 120 cubic inches per hour / 200 square inches = 0.6" per hour. The wetting area is the tricky variable since it depends on soil type, etc. With the relatively porous soil I am using in my planters I found that even 12" spacing created dry spots so I started using 6" everywhere. Not sure I’ve nailed the settings and I’m not a gardener but so far some pumpkins are growing pretty happily in the hot Arizona summer, so maybe the settings aren’t too far off.


#4

Here’s a pumpkin on the 6" drip line - it was planted in June. Currently I’m using AW = 0.12, root depth = 12", AD = 35%, efficiency = 80%, Kc = 100% in this zone.


#5

I’m using 6" spaced inline embedded drippers too. I put catch cups under several of the drippers then averaged them out. I plugged it into an online calculator and it put me at 0.77 in/hr. Pretty close to your numbers, but you probably spent less time in getting yours. I’m an engineer, so here’s my geek data.

Using the calculator here, I was given the 0.77" number.


#6

My garden is not planted right now, but when I was last using it the settings were AW = 0.17, root depth = 6", AD = 50%, efficiency = 90%, Kc = 100%.

I have pure potted soil in a veggie box, so I think the higher AW makes sense than your in-ground setup. I thought about playing around with a lower AD number for my veggies, but given that I went to a fixed schedule I didn’t go that route. We have the same Kc. I have a lower root depth, but that box isn’t even 12" deep, and I don’t have pumpkins!

I’m amazed that you can get that thing to grow in that spot. It seems like the sun bakes into my concrete pots and pavers, making them like a clay oven. I’m always surprised we can get anything to grow out here in this summer. Kudos, your pumpkin looks quite healthy!


#7

Looks like that calculator is just taking 0.319 gallons, converting to 73.689 cubic inches, and then dividing by 16*6 = 96 square inches to give you the 0.77" number. This seems to assume that the drippers will wet the entire space between dripper rows. When I was using 12" spacing I didn’t get full coverage between drippers for my soil so I don’t think that calculator’s assumptions always hold. We can account for this lack of uniformity in the efficiency number but then we might have to know how much water was getting to different locations via capillary action which isn’t as easy. So I just guessed at an 8" circle for the area per dripper and left the default efficiency. At one point I also geeked out and measured the actual drip line output but I think it was pretty close to the spec value in my case.


#8

Thanks! That’s nice of you. I’ve had pumpkins get to August before and then kick the bucket, but now that I have a Rachio I’m hoping things turn out better. They are certainly a challenge here.


#9

I agree completely. The volume divided by area thing doesn’t always quite work out for drip since the vertical displacement is deeper under each emitter as compared to the outer edges. I guess that’s why it’s always important to understand that regardless of the method we use to get the initial in/hr number, it’s always worth considering tweaking the number as needed.


#10

Thanks for the input here. I’ve adjusted the Advanced settings on my veggie garden’s zone, bumping the root depth up from 10" to 12" since an online source said tomatoes have 8-12" roots and corn has 12" roots. I also bumped the Crop Coefficient up to 100%. I have no idea what Crop Coefficient is, but 100% seems to be a common rate in the responses I received, so let’s give it a shot. :}

I’m surprised that you’re doing OK with twice a week.<

Azdavidr, it does get pretty hot out here in the Sacramento valley, but I’ve heard that deep and infrequent waterings are the way to go. But I’ll admit that the poor plants do look pretty wilted and stressed between watering days. As for your chart, thanks for posting it, though I haven’t a clue what to do with it. Once numbers start flowing in a conversation, my eyes just glaze over. Math just ain’t my thing. :confused:

Idslaron, those pumpkins do look nice. I hope you get some keepers by the time Halloween rolls around.


#11

While not apples to apples, growing up we had quite the garden and the only watering that it recieved was the flood irrigation that came every two weeks. Look at all the farmers here in Arizona. Most of the crops are only watered on the same schedule. Not a lot of areas around here utilize newer methods of sprinklers, drip tape, etc.


#12

@Raymondo17, crop coefficient is a measure of how quickly vegetation uses the water available to it. As a result, a higher Kc will change your schedule such that it waters more frequently. Don’t worry about my spreadsheet numbers. That was more for @ldslaron as he and I both speak geek.


#13

Was that geek or leet?


#14

Definitely ‘geek’ ! The other one I had to google. :wink:


#15

I guess my geekiness is showing now.:nerd:


#16

Sorry - I have a bit of a “Math Curse”… Good book if you have kids by the way.

For starters maybe fiddle with crop coefficient if things just generally aren’t getting enough water. Note that if you increase root depth you will put down more water on each watering but also go longer between waterings, all things being equal. Unless your tomatoes and corn are mature I’d keep allowed depletion fairly low to avoid drying them out between waterings.


#17

We have so many different types of vegetables, with academic root depths ranging from 3-6 feet to only 4 inches. Different plants have different desires for wetness, some are just germinating while others are fully developed, etc.

Makes it impossible to get the canonical correct settings by measurement, so I set the root depth to a middle value, faithfully entered all my soil properties, and modulate AD/Kc, run manually, and water by hand based on frequent observation of crop health & soil moisture. In future years I plan on addressing variation in crop need with emitter design & bed groupings.

It has by no means been maintenance-free, but hopefully in the end once I settle on empirical settings it will work well.

Total water usage in the garden is a rounding error compared to our tree & bluegrass usage, so for the garden I’m really more interested in plant health and rain skip than perfect efficiency.

Tomatoes, FWIW, despite their reputation as water-hungry have extremely deep roots and need to dry out between waterings. They don’t like swamps. We nearly killed one this year by overwatering with the hose.