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krishnaraoji88

Rainfall versus irrigation

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krishnaraoji88

Hi all,

Got to thinking, how many inches of rainfall really decide for you if you need an irrigation system? I know there are variables like tropical vs maritime, clay vs sand, distribution, etc. I also know some palms like Brahea need minimal water yet others are water hogs. Just wanted to get some thoughts on this!

-Krishna

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Dypsisdean

It is not really a factor of "how many inches of (yearly) rainfall" you need. (I assume you mean yearly rainfall) It is more a factor (IMO) of how evenly throughout the year it rains.

Example: I get about 60 inches/yr. here in Kona mauka. If that worked out to be 5 inches a month, spaced out to 2.5 inches every two weeks - I would be golden. But some years that might mean 10 inches in Aug and another 10 inches in Sept. while getting close to zero in Jan. and Feb. And since 60 inches is an average, I may get 30 inches in a super bad year, and 90 in a wet year.

So, you really have to figure out your worst case scenario in your driest months - not yearly average. A month without rain in Hawaii and things start to suffer. Two months (or less) without any rain and some "water loving," smaller understory, or not yet fully established palms/plants, start dying. So you may only use your irrigation a few times a year, but it may end up saving your garden.

Of course if you have a smaller garden and water is available, you can always resort to hoses and sprinklers - provided you are around (don't depend on a house sitter). For me (3 acres), there is usually once or twice a year were I would be screwed without my irrigation system. And I can put it on auto and leave town without worry.

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krishnaraoji88

Thank you! I really appreciate the detailed response (particularly hawaii specific). Im planning on relocating to a new neighborhood on the Windward side (bringing my best plants with me) but its coastal so it gets only like 40-50 inches a year. Most of the houses don't have irrigation from what Ive seen but I think they get pretty beat up during the summer. I know the groundwater is high as its near Kawainui Marsh but I don't think that will be enough for most plants so I may need to invest in an irrigation system...

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bgl

Totally agree with Dean. A good example being the old Sullivan garden in Kapoho, later purchased by Mark Frost and sadly lost to the 2018 lava flow. Terry Sullivan installed a very elaborate irrigation system at their 11 acres, despite the fact that average annual rainfall is between 80 and 90 inches. Problem being that Kapoho is hot, sunny and quite windy and at times there's no rain for several weeks and during that time pretty much everything dries out - unless you have irrigation.

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richnorm
1 hour ago, bgl said:

Totally agree with Dean. A good example being the old Sullivan garden in Kapoho, later purchased by Mark Frost and sadly lost to the 2018 lava flow. Terry Sullivan installed a very elaborate irrigation system at their 11 acres, despite the fact that average annual rainfall is between 80 and 90 inches. Problem being that Kapoho is hot, sunny and quite windy and at times there's no rain for several weeks and during that time pretty much everything dries out - unless you have irrigation.

That's terrible news that somehow passed me by.  

Re irrigation, couldn't agree more.  I can go years without using mine but when you need it  being able to turn the drip on for a few hours seems well worth the effort of the install.

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James760

Any recommendations on getting a drip irrigation system kit online? Going to install one myself here soon. Thanks :greenthumb:

James

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krishnaraoji88

Sounds like everyone on here thinks drip is best? What do you do for the grassy areas of your lawn (if you have any)

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richnorm

Not sure about suppliers but it shouldn't be an expensive exercise as these are manufactured in huge numbers for the horticultural indiustry. If you have slope then pressure compensated emitters are much better.  Going for the lowest rate dripper available will allow the maximum number on one line.   I run several hundred 2 lph drippers on a single tap.   

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James760

I have to run about 900 ft of line with atleast 100+ emitters. ( rough estimate )

Oh, am going to trench the line about 6in. Deep as well... fun times ahead :floor2:

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