Give them an inch and they’ll take 1.8 liters

Watering plants is a complex exercise where many variables come into play. What’s your soil? What is the variety of the plant? What time of the day is it? Do you feel like watering when it’s hot and you’d rather be inside in the air conditioned house watching tv? Eventually, after many seasons, you develop a sixth sense about it and your garden thrives. Until then however, you are a novice and you depend on the advise from people who have killed more plants than you have.

For tomatoes, one rule of thumb I often read is: Tomatoes need 1 inch of rain per week. Well that’s all fine and dandy but if it doesn’t rain then you have to figure out what an inch of rain means in terms of volume; one gallon, two gallons, 6 liters? Well, as it turns out, the answer depends on how much area you need to water.

When the weather guy on tv tells me that it rained an inch last night, he means that if the water did not go anywhere and just collected, there would be one inch of water standing in my yard. Now you see why the area matters. If I collect all the water from 1 inch of rain from a large yard, it will be more volume of water than if I collect it from a small yard.

So, I went outside and drew a 12 inch circle around one of my tomato plants and imagined that there was a cylinder 12 inches in diameter and one inch high. A little math and voila! I had my answer: 113.14 cubic inches or approximately one half  American Gallon of water (British Gallons are different and that’s why I like the Metric system better). This is about 1.8 liter.

HALF A GALLON A WEEK!!!??? Are they crazy!? Even with mulch my tomatoes would die if I only gave them half a gallon of water a week! In the nasty, 100+ degree (F) weather we get around here in the Summer, I would have to do half a gallon every day.

Here’s a more detailed chart on watering tomatoes that I got from the Allotment Vegetable Growing website. It’s in liters and pints. Here in the U.S. one gallon equals eight pints.

Water Requirements of Tomatoes
Weather Conditions Liters per Day Pints per Day
Very dull, cloudy or dull for most of the day 0.14 -0.28 0.25 – 0.50
Fairly dull, overcast for most of the day 0.28 -0.42 0.50 -0.75
Fairly sunny, cloudy at points with bright periods 0.71 – 0.85 1.25 – 1.50
Sunny, just occasional cloud cover 1.10 -1.20 2.00 -2.25
Very sunny, clear blue skies all day. 1.50 -1.80 2.75 -3.25

Of course, none of this means a hill of beans if you’re growing your tomatoes in a bucket.


After much deliberation I chose the Nikon D5000 with an 18-55mm lens. I had originally looked into a 4/3 micro type of camera but at the end this Nikon won me over with all it’s features. I bought it at lunch time today and I can’t wait to get home and play with it.

Nikon D5000 DSLR

Nikon D5000

Posted in Spring. 5 Comments »

5 Responses to “Give them an inch and they’ll take 1.8 liters”

  1. Chris Says:

    That’s why I love the Earthbox–no guesswork!

    Congrats on the DSLR. I just made the jump from point-and-shoot to a Nikon DSLR myself last Christmas. You will have fun with it.

  2. Gardener on Sherlock Street Says:

    Ooooooh! Love the camera!!!
    Great job on all the water calculations. My mathematical husband would be very impressed. My “experience” is anything in a pot needs more water and wind is killer to tomatoes if they don’t get a steady supply of water.
    Have fun with the camera this weekend.

  3. yaquigrande Says:

    Yeah, I like my sub-irrigated containers too!

    Thanks! You’re right about the potted plant’s water needs and I will have fun with the new camera!

  4. Princessdiva Says:

    I had to crack up at your comment about taking the advice of people who have killed more plants than you have!! HAHA! Many of my friends are either non-gardeners, or beginning gardeners–and in 16 years of gardening–I find myself telling lots of plant death stories when they ask for advice! Well put!

  5. bangchik Says:

    It would be fun to put meaning behind gardening in mathematical form….. However, I rather treat gardening in a casual way.., depending on feel rather than exactness…
    Have a great weekend. Cheers ~bangchik

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