That amount sounds good to me-my soil requires a quick soak per hose every day as I walk the length. I have clay/improved with compost but not ideal.

A mature plant could probably use a few gallons. The plant's roots can extend out several feet in every direction. I'd apply 2 gallons out 3-4 feet around the plant, wait 10-15 minutes, then apply 1 gallon to the same area. Use a watering can with a rosette to keep the stream gentle and even.

Hi Plantslayer,

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!

A mature tomato plant's root will cover more than a square yard of space, so it is going to need about 5 gallons of water a week, and you did not say how often you were applying that "about 1 gallon per plant space per watering, applied slowly enough to soaks in without running off". If you are doing that every day or so, you'd have about 7 gallons per week, but what you would be doing would be watering shallowly and training your tomatoes to grow roots near the surface. Not an ideal solution. I'd prefer that my tomatoes had a cubic yard of root space rather than a square yard.

Now if you can put 5 gallons of water on each plant on a weekly basis, that might work except for the fact that nature abhors a vaccuum! If you put 5 gallons of water in a square foot of space, it is going to naturally migrate to the drier areas. You can't just water to a certain point without some physical barrier (such as a container.) So, 5 gallons a week just at the stem of a tomato is going to be insufficient. The area that normally acts as a resevoir will instead act like a sponge and draw the moisture away from your plants if it is drier then the root area is.

For in gound plants, you need an inch of water on their roots and the surrounding area. (Probably at least 3 to 4 feet all around the plants.) So probably more like 10 gallons of water per plant.

Betsy

Thank you for your advice, Betsy. I must say, though, that 10 gallons really does seem like a lot of water in one watering, even if I do need to water deeply. I think it might make more sense out in the field, but the garden soil in this urban plot only goes down two feet at most there (I don't know what they have under the top soil in our beds, it may clay or just compacted hard soil, not sure). If I were to put 10 gallons on each plant I'd simply be soaking the entire plot.

I think you are right about 1 gallon not being enough for a good watering, though. Given the length of time I let the hose sit on each plant it must have given them at least 3 gallons or more. I'll see if I can find a way to estimate how much they have been getting... so far they seem healthy and have grown quickly, so they must have been getting enough water. I hope so, anyway. In a setup like this I need to be concerned about giving them wet feet too.

plantslayer - you said "Since advice always tells you to "water deeply" it seems to me it is best to base watering volume on spacing/soil characteristics, and then chose when to water based on how dry the soil feels according to the finger/stick test. Is there any flaw to my reasoning here?"

That's the best reasoning of all. IMHO nobody can really tell you how much you need to water unless they're in your immediate locale undergoing the same conditions.

Current weather, recent rainfall, soil characteristices all play a part of how often and how much you need to water. You have to fake it! Look at the soil and your plants. They'll tell you how they're doing. Wilty plants and dry soil down a ways? Probably not enough water. Upright, green shiny leaves and the dirt is moist? Just about right. Does it look like the Creature from the Black Lagoon is about to climb out of your patch (boggy, wet soil)? You may be overdoing it with the water.