How Much is an Inch of Water?

yodianaJuly 12, 2011

In regards to gardening, I've read things like, "During the fruiting season they'll (strawberries) need around an inch of water each week."

I've read/heard this on several occasions and thought "an inch of water" meant that you kept watering the (container) plant until there was an inch of water above the soil. But that doesn't really make sense. What if the pot is super large? Or the water never sits an inch above the soil? Wouldn't this cause over-watering?

Can someone please explain to me how much "one inch of water" equates to?

The correct response will solve a long time mystery for me. Thank you in advance for your help!

Here is a link that might be useful: Strawberries Growing Conditions

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penfold2(4b, MN)

An inch of water refers to the amount of rain or equivalent irrigation that plants in the ground should receive. If you were to place an empty container next to the plants, it would have an inch of water after irrigation. This doesn't really apply to containers though. They should be watered until the pot drains significantly. The only question is how often to water, and this depends on several factors such as pot size and soil type. Water usage is much more variable in containers than in the ground, so no one can tell you how much water you'll need. You just have to check the containers and figure it out for yourself.

    Bookmark   July 12, 2011 at 2:03AM
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My dad said to put a tuna can next to my roses and water till the can is full which would be about an inch. He swears that roses should only get about an inch a week and mine were alive when I did that but when I water daily or every other day, they bloom like crazy. The roses are in the ground though. Containers need a lot more than that...or at least more often. I have my strawberries in hanging baskets and the guy at the nursery jokes that you should water them till they pee (meaning there's water dripping from the bottom of the basket). I've read that it's better to give most stuff a good soaking less often rather than giving them a little drink more frequently. That doesn't really make sense to me but what do I know? When it was a little cooler here, I would stick my finger in the soil up to my second knuckle and if it was dry, I'd water. Now I pretty much just water every morning because I know it's going to get up to 100 degrees and if things are looking wilty in the afternoon and there's no storm coming, I'll water again. I'm not really sure that's right, but it feels right. It's making my dad absolutely crazy when I talk about watering once or twice a day because he says that's way too much but almost everything is thriving so I must be doing something right!

    Bookmark   July 12, 2011 at 2:23AM
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dickiefickle(5B Dousman,Wi.)

Googled found this:

A rain gauge collects falling precipitation and funnels it to a rain measurement device. In a standard manual rain gage (one that has to be manually emptied), the rain measurement device is a graduated cylinder. In home weather stations, a self-emptying tipping bucket rain gauge is the most common type of rain gauge used for rain measurement. The reading is then transmitted to the inside console for recording/display of the information. This is done either wirelessly using radio waves (wireless rain gauge) or via electronic cabling. Stand alone wireless rain gauges are also available.
Rainfall rate is generally described as light, moderate or heavy. Light rainfall is considered less than 0.10 inches of rain per hour. Moderate rainfall measures 0.10 to 0.30 inches of rain per hour. Heavy rainfall is more than 0.30 inches of rain per hour.
Rainfall amount is described as the depth of water reaching the ground, typically in inches or millimeters (25 mm equals one inch). An inch of rain is exactly that, water that is one inch deep. One inch of rainfall equals 4.7 gallons of water per square yard or 22,650 gallons of water per acre!

    Bookmark   July 12, 2011 at 3:41AM
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Thanks for your responses everyone!

Penfold2, thanks for clarifying that its mostly for ground plants. You said, "If you were to place an empty container next to the plants, it would have an inch of water after irrigation." Wouldn't it require more rain to reach an inch in a wider container than it would a narrow one?

btbarbara, I have roses in the ground too but didn't understand the tuna can example. Are you watering directly into the can? If so, how do you make sure you're watering the roses the same amount of water that you're pouring into the can? I, too have heard - it's better to give most stuff a good soaking less often rather than giving them a little drink more frequently. It makes sense to me but I don't think my plants know that. They're either too wet or too dry when I do this. I'd give them less more frequently if it weren't for fear of salt build-up. I'm still at a lost.

dickiefickle, I think I came across that while googling too. Where I get confused is how to reach that one inch? Doesn't the rain water get soaked into the ground before we can account for it?

Since most of my plants/trees are in containers, I shouldn't concern myself too much with "an inch of water a week." But I'm still having a really hard time determining what the "perfect" amount of water is for each of my plants. And to make it even more challenging, they are different plants, in different size pots, etc..

I do have well-draining soil. I tried using a moisture meter but don't think I'm using it properly since I'm getting different readings when I insert at different levels/places in the soil.

I've used my finger but the soil always feels super dry on top and wet at the bottom. And I must not be understanding the chopstick method either since there's always something sticking to it whether its wet or dry - what am I suppose to be looking for?

I have a Early Girl tomato plant that looks over-watered to me (by sight and touch of the soil), However, if I don't water it daily it wilts but will perk right back up within an hour of getting water. The other two tomato plants (in same size 10 gallon pots) look fine and never wilts. So I'm not sure if I'm suppose to water them the same time I water the Early Girl?

    Bookmark   July 12, 2011 at 1:33PM
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redshirtcat(6a MO StL)

With a sprinkler it might take longer depending on how the sprinkler is calibrated and where the dish is positioned but the idea is that when it rains the water is relatively evenly distributed. Meterologists measure the rainfall with devices (slightly more complex than the simple dish usually). Sometimes spinkler professionals will measure output of the system in inches as well (usually using the dish method).

For my roses I have soaker hoses that surround each plant and I turn those on once a week for an hour. I've never measured the output but it's a good deep watering once a week. They do very well in 6a with that treatment. I wouldn't want to try to top-water roses because I want as little splashing as possible to help keep diseases in check (botrytis, blackspot, etc) - I strongly encourage you not to use a sprayer or to top water roses. Go with drip or soaker hoses.

There is no "perfect" amount of water that will be appropriate for all plants in all containers. The moisture meters are actually measuring EC and converting it to an approximate moisture but they are reasonably accurate. They will always read dry in the top inch or so of soil (because it's usually dry). The moisture content in your pot probably goes up as you push the probe deeper. In soils like the gritty mix (where the probe won't read properly btw) you will find that the moisture is much more evenly distributed. The top will still dry out quickly but underneath the air-dried layer you will find even moisture because there is no perched water table. It is almost certainly the case that your "well-draining" soil is supporting a perched water table and you will read "very wet" on a moisture meter as you go down.

I'd stick with the moisture meter until you can tell by sight/touch. I would push it down at an angle and I would ignore readings above, say, 2". If possible you want your meter to read "moist" and not "wet." It's very likely your soil will make that impossible.

Next year you might consider a self-watering container for tomatoes. They take a *lot* of water and it can be hard to keep them evenly watered during the day when they are in pots. Here's a video I made for someone else in another thread but a minute or so in you can see my Early Girls in Earthboxes and in Earthtainers: My tomatoes and peppers in the gritty, 5-1-1, and earthbox/earthtainers

1 month ago they looked like this:

    Bookmark   July 12, 2011 at 3:04PM
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penfold2(4b, MN)

Wouldn't it require more rain to reach an inch in a wider container than it would a narrow one?

Yes a wider container requires more rain, but it also has more surface area to collect rain. As long as they have vertical walls, you could put containers of any shape out in the rain and they would all have the same amount of water in them.

I have roses in the ground too but didn't understand the tuna can example. Are you watering directly into the can? If so, how do you make sure you're watering the roses the same amount of water that you're pouring into the can?

This applies more to rainfall and sprinklers which water relatively evenly over a large area. If you were to do it with a watering can, you'd have to try to water the plant and can evenly in order to get an accurate measurement.

I, too have heard - it's better to give most stuff a good soaking less often rather than giving them a little drink more frequently.

In the ground this encourages deep roots, which makes plants more resistant to drought since deeper soil doesn't dry out as fast. In containers it does the same, plus it allows excess minerals to be flushed from the pot.

Where I get confused is how to reach that one inch? Doesn't the rain water get soaked into the ground before we can account for it?

You would use some type of rain gauge or container if you wanted to measure it. Weather reports often give rainfall in inches, so that would tell you as well.

I have a Early Girl tomato plant that looks over-watered to me (by sight and touch of the soil), However, if I don't water it daily it wilts but will perk right back up within an hour of getting water.

I've experienced the same thing. On hot days I have to water my tomatoes even when the soil surface is still damp. I think they simply transpire so much water that the middle of the container actually dries as fast or faster than the top. Either that or the sun heats up the pots reducing root efficiency, which is then alleviated by watering and cooling the pots down again.

    Bookmark   July 12, 2011 at 5:43PM
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Hey redshirtcat & penfold2, thanks so much for the response. Very much appreciated. I love this forum!

@redshirtcat - my gardener just tore out the drip sprinklers from my rose garden because they kept getting in the way of him tilling the soil. I got tired of the hoses being torn out of place after his visits so I agreed to it; bad idea. He replaced them with regular sprinklers that shot water everywhere so I had him replace with a less powerful spray. I'm sure you can guess that my roses have black spots now. Sigh. Thank you for explaining the moisture meter - its exactly as you've described. Although I had to look up "perched water table," it does make a lot of sense. I have been able to get the moisture meter to read, "moist" a couple of times. But by then, the plants looked like they were on the brink of death from dehydration.

My so-called "well-draining" medium consists of mainly of Supersoil Palm & Cactus mix, perlite, gypsum and very little outdoor potting soil (Home Depot's Kellogg Patio Plus).

Did I make you cringe reading that? Am I wrong for assuming this mix is well-draining? I would love to get Al's or the gritty mix but had a really difficult time finding all the materials. Everyone I've asked has never even heard of turface. The pine fines are hard to locate too.

Cool videos! You mentioned in the video that you used Axis instead of Turface and Pine Mulch instead of Pine Fines? Were you able to get both at Home Depot? That sure is a small pot for the tomato plant - what size is the pot? That's another concern of mine with the gritty mix - its TOO well draining. I don't know if I can afford to water a tomato plant a couple times a day. Can you put a tray underneath that pot? Will the gritty mix wick up some of the water that drained out? Are your pots heavy? Wished my plants looked nearly as good as yours!

@penfold2 - Thanks again for responding. I "realized" most of the answers after I had posted. In regards to your tomatoes, may I ask if you water ALL your tomatoes at the same time or only the ones that have wilted or look like they need it? Only my Early Girl tomato wilts. The others look fine so I'm not sure if I should go ahead and just water them too? Earlier in the season, my tomatoes had bad cases of blight. I was actually waiting for them to die off so I can disinfect the pots and use for other plants. But for some reason they survived and are probably the greenest best looking plants I'm currently growing (not saying much since most of my other plants are diseased or dead). Ha!

    Bookmark   July 12, 2011 at 6:51PM
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penfold2(4b, MN)

I have an Early Girl and a Big Boy and they are both in the same size containers and both seem to wilt at the same time, so I water them together. If they wilted at different times I would water them separately.

    Bookmark   July 12, 2011 at 7:04PM
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Thanks much, Penfold2!

    Bookmark   July 12, 2011 at 7:07PM
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redshirtcat(6a MO StL)

eek. The only thing that made me cringe was sprinklers! Taking out drip to put in sprinklers that get the roses wet, eek.

With respect to drainage: I guess my thinking is that it's not enough for a pot to drain quickly (and I don't know that yours does even that) - it can drain out the water that the soil won't support and you can still be left with a water table inside. You can test for this by watering, allowing the pot to drain fully, and then tilt it to about 45 degrees and watch for any new water draining out. When you tilt the pot you reduce the potential size of the perched water table so some (not all) of the perched water drains out. It is almost certainly the case that your soil is perching water if you read "wet" in the bottom and dry in the middle.

I prefer to use soils that support less of a PWC (gritty, 5-1-1) or use self-watering containers where I don't really have to worry about unevenness in the pot.

The gritty will not wick at all - so a tray won't work. The 5-1-1 will wick to a certain extent. How much wicking and water retention you get depends on the size of your pine fines.

I only know any of this because I read Al's posts and have tried out his suggestions most of which work well for me. You can read his post on water movement in pots here

The tomato in the gritty mix is in a 5qt pot. Way too small, don't do that. I wouldn't even start with tomatoes in the gritty it might be too discouraging. Though it is nice to be able to water the plant without any fear of over watering.

You give your zone but not your city - I suspect no matter where you are that you can find most of the necessary ingredients. Certainly you can find the substitutes. 10 is like South Florida and Texas, right? Should be available if you're interested in trying. You can check this thread for hints on where to look:

If you want to try building your own soil I would start with the 5-1-1. I would look around for pine fines again. Call nurseries and ask if they have suppliers. Call landscaping companies and suppliers. Check the wholesale nursery suppliers and building/material suppliers. Also remember that pine fines can sometimes be found bagged in big box stores under the name "soil conditioner" - check to be sure that it's actually pine fines though. In south TX/FL pine might be hard to come by but I'd still give it a good look. If you still can't find any then you can use pine mulch but only if it looks like this: what I use in place of pine fines

For the roses with black spot: I've found Serenade to be very effective. This is a preventative measure - it won't cure infected leaves (pull those off, careful not to touch clean ones). I tank mix Serenade with a variety of other fungicides and spray once a week. Serenade is always in the mix (I alternate Daconil, Rose Pride, Bayer Advanced etc depending on heat conditions and to prevent resistance). Serenade is by far the least toxic. Some people use Neem but I have lacewings so I prefer the straight fungicides.

I've been using Serenade on my tomatoes as well. Again, once a week (don't use any other fungicides on'll be eating them).

So far this year I have 0 black spot and 0 blight. I do get a little botrytis on the rose blooms when it's very wet but that's because the ones that open mid-week aren't protected.

    Bookmark   July 12, 2011 at 9:20PM
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@redshirtcat, thanks for taking the time to explain things in layman's terms. I've learned so much in these forums but sometimes get overwhelmed with all the new knowledge so I really appreciate the "hand-holding."

Other than the weight of the container and watering requirements with using the 5:1:1 - I'm not sure if I can repot as often either. I read that those mixes are for short term plantings of just 1-2 years?

I'm in San Diego, CA. Pretty certain that I will be able to find all the materials here; somewhere! I went to the link you provided and someone from San Diego said they found the ingredients at the local John Deere branch, so I emailed the branch with my request. Yay! Thanks for encouraging me to give it another go.

For my roses, I've found Bayer Advance All in One Rose & Flower Care worked really well. I will have to check my calendar but it says to apply every six weeks and I don't think I'm at that mark yet. Wonder if I will do any damage if I applied the systemic at 5 weeks instead of 6?

As for the fungicides, I've used Daconil once and it turned all my plants/roses white! People who never noticed the black-spots definitely noticed the ugly "white residue" on all the plants. It was a huge mess. I'm still waiting for the white blotches to grow out. So unless I didn't mix or apply it right, I'm scared to use it again.

Wished I would've known not to use Daconil on tomatoes (even though that's what I originally bought it for). I'm still having to throw away perfectly good tomatoes with white residue on it. Why do they market it for tomatoes then? Or was I not suppose to apply it when it is fruiting?

Serenade is on my "shopping list," thanks! Have you heard of "Actinovate" biological fungicide? I've read (on GardenWeb and other places) that it was a really good product. I'm interested in using it as a foliar spray and soil drench for plants that may have possible root issues/rot.

Thanks so much again for all your help. New subscriber of your videos!

Here is a link that might be useful: Longer term plantings

    Bookmark   July 12, 2011 at 11:43PM
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phucvu(10 b oc ca)

i got this advice on watering, use about at least half the amount of the containter, i.e. if you got a 5 gallon container use at least 2.5 gallons of water twice a week.

    Bookmark   July 13, 2011 at 12:42AM
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@phucvu, are you watering with at least half the amount of the container on your plants? If so, how long have you been doing this and have you been successful? What size containers are you using? Never heard of this but sounds easy enough, if it works. Thanks!

    Bookmark   July 13, 2011 at 8:18AM
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redshirtcat(6a MO StL)

Sorry, just to be clear - the 5-1-1 is bark,peat,perlite - so the weight isn't a problem (unlike the gritty mix which is 1/3 granite or similar). The 5-1-1 should be very comparable to your peat-based mixes in terms of weight and will weigh less than those mixes when wet as it will hold less water.

The 5-1-1 will perform better than any bagged soil you will buy (some professional Fafard mixes might be comparable). When Al says it's for annuals and will be good for 1-2 years that doesn't mean it isn't much better than anything peat-based. Just that after 1-2 years the 5-1-1 will start to perform like the peat-based soils as the bark breaks down into finer particles. You've still gained several years of better growth.

Now if you're comparing it to the gritty mix then yes you'd be better off in the gritty mix with a long-term planting. If you can deal with the additional work (more watering, dealing with runoff if the plants are ever indoors, sourcing, weight, etc).

I don't use the BA systemic so I can't advise you there - I use their straight fungicide. I think your Daconil problem might be related to heat - if I recall correctly you need to apply that in lower temperatures but check your label since sometimes I confuse them. Some roses are also more sensitive. But I've never seen any sensitivity with Serenade (though you could have resistance problems if you use only serenade). I've never tried Actinovate but I read a thread where Raybo compared Serenade and Actinovate and I saw him suggest the Serenade in his Earthtainer guide so that's what I picked up. It's working very well.

Daconil is widely used and is labeled for all sorts of vegetables. I hardly qualify as an organic grower but when I read about Daconil I really don't want to be spraying it more than I have to. "Probable human carcinogen," chronic exposure caused kidney damage and tumors in animals, etc. Check it out for yourself and decide...

    Bookmark   July 13, 2011 at 9:27AM
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phucvu(10 b oc ca)

i've been doing it for about a month ever since talking to the guy selling trees at a swap meet.



    Bookmark   July 13, 2011 at 5:26PM
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@Hello redshirtcat. I was using the terms, "Al's Mix," "gritty mix," and "5:1:1" interchangeably - not really knowing what the difference was. Now I know! Except which one is "Al's Mix?" And glad to hear that the 5:1:1 won't be any heavier than the medium I'm using now. Phew!

Great news! A John Deere rep contacted me and said they had all three materials. This is what he said, "I have the Turface MVP, except we call it Allsport. Comes in a 50 lb bag and is about 10.50 per bag . I have Orchid bark 2 cu ft bags and it is 7.65 a bag . The peat moss is in a 3.8 cu foot bale and is 15.70. All good in stock." Their shop is less than 10 mins away so I'm hoping to go pick those items up tomorrow. Have no idea what the size/weight of each bag so hope I can get them into my car. I'll also have to re-read the posts on 5:1:1 to make sure I'm properly mixing. Just hope the plants/trees won't be too upset with me for repotting so soon again. Thanks for encouraging me to look for the 5:1:1 again!

Went to Home Depot this evening and couldn't find Serenade. I'll go to a nursery and see if they carry it. I'm guessing you're not getting the white-residue when using Daconil? A few people on here had my experience with Daconil so I was beginning to wonder if the white-residue was "normal." I'm also going to give Daconil another try but will mix it with the Serenade. THANK YOU redshirtcat!

@phucvu, thanks for the photos. Nice trees! Will you be keeping your bearss lime in the container? If so, what potting medium are you using?

    Bookmark   July 14, 2011 at 4:33AM
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redshirtcat(6a MO StL)

I think there is still some confusion. Peat, bark, and turface are not components in the same mix (that we've been discussing).

The 5-1-1 mix is partially composted pine bark fines, peat, and perlite. The peat would only be used in this mix and only in small quantities.

The gritty mix is uncomposted pine bark, turface, and granite (or similar). Particle size matters in this mix. The turface and bark could be used in this mix if they are the correct size but you'd still need granite of the correct size. Do not put peat in here.

Both of these are "Al's" mixes. You can find the reasoning behind the soils here.

What is in the orchid bark? Is it pine/fir bark? If so then you still need to pay attention to size - if not, I'd find another source of bark. You want some kind of conifer bark since it will contain the lignans that help it last longer.

I think you should read the thread linked above an then decide which soil you want to try and then we can talk about how to make it? Or you can find threads discussing them both if you look around.

It looks like you might be confusing the 2 different soils now so maybe hold off on buying anything until you know what you want to do...

I've had no issues with Daconil leaving a white residue on my plants. I did ignore the heat warning once and had some phytotoxicity on one rose bush as a result. Daconil is used in very small amounts per gallon, are you sure you're using the right amount? To get a white residue I think you'd really have to use a lot... 1.25 fl oz per 4 gallons according to my label. That's just under 2 tsp per gallon. Was the white stuff a residue or a reaction in the leaves? If it's a residue I'd double check your mixing rates... and make sure to keep your sprayer agitated. I've never seen a residue from any fungicides I use. Not even the bright blue copper ones...

Again, be careful with the Daconil in the heat...

    Bookmark   July 14, 2011 at 12:55PM
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phucvu(10 b oc ca)

no special mix, just the dirt i dug from the ground to put another plant in and it still drains really well. it will be in container i guess, because limes are cheap and not that rare or useful unless you are vietnamese like me and need them for the fish sauce hehe.

i'm not saying that the growth is due to the watering, but it didn't hurt, plus i got it for over a month before talking to the guy without any new growth so it might just needed the time to adjust to the new environment.

what i don't get is the size of the container. some are labeled 5 gallons, but no way it's the size of the 5 gallons water bottle, maybe 3 gallons at most.

    Bookmark   July 14, 2011 at 4:12PM
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