[Mudge]

I spotted here a few weeks ago someone saying water from the bottom, feed from the top.

Can someone explain why? Does it make a difference?

All my toms are being watered from the bottom at the moment and I was going to feed the same way.

Thanks.

[Yorkie]

I think it's to do with different types of roots.  The small feeder roots are in a different location to the watering roots.

Or something like that 

[azubah]

I spotted here a few weeks ago someone saying water from the bottom, feed from the top.

Can someone explain why? Does it make a difference?

All my toms are being watered from the bottom at the moment and I was going to feed the same way.

Thanks.

When it rains, all of my garden gets watered from the top.

[mumofstig]

Indeed, but it doesn't rain every day (hopefully)  :blink:
Usually long roots go down in search of water but the richest soil is nearer the surface and the roots there absorb nutrients.

[JayG]

I believe this practice is more to do with ring culture of tomatoes which I don't know much about, but the principle is that an extensive root structure is encouraged by planting in bottomless pots over wet gravel - the feeder roots are in the pot area so are fed, the water is mostly taken up via the gravel.

Certainly not practical to do it growing in growbags - easier in pots but whether it would produce any of the benefits of ring culture I have no idea. 

[andyf75]

when should you start feeding tomatoes?

only once the fruits are developing or before then?

[mumofstig]

If you've been potting them on every few weeks or so, as they've got bigger, then they shouldn't need feeding until they have the first flowers set (tiny green toms showing)

If however they have been held in small pots because of delayed planting/space/weather issues
then it's probably worth giving them a feed at half strength just to stop them struggling.