I sprayed my lawn (hose-end sprayer) with a liquid lawn fertilizer
(20-3-4) and some over-spray probably got on a few potted tomato
plants. The area was heavily watered the day before.

The next day I noticed the tomato plants looked somewhat shriveled
without actually being wilted or droopy.

The fertilizer contained no herbicide or weed killer. Just 20%
nitrogen, 3% Phosphorus (Phosphoric acid) and 4% soluble potash.
Would something like this be harmful to tomato plants?

At the peak of summer, that much nitrogen fertilizer is bad for
anything. Plants are either trying to go dormant in the heat, or divert
energy to surviving the heat. Fertilizing with nitrogen-rich fertilizer
forces them into growth cycles, and stresses them out. Your lawn is
going to need a lot of extra water now, too. This is the wrong time of
the year to be fertilizing.

--
Warren H.

==========
Disclaimer: My views reflect those of myself, and not my
employer, my friends, nor (as she often tells me) my wife.
Any resemblance to the views of anybody living or dead is
coincidental. No animals were hurt in the writing of this
response -- unless you count my dog who desperately wants
to go outside now.
Blatant Plug: Books for the Pacific Northwest gardener:
http://www.holzemville.com/mall/nwgardener/index.html

This summer so far we've been cooler than normal (great-lakes area).
And wetter than normal. Nothing is going dormant around here. Last
summer I watered like crazy in July and August. Not this summer.

Still doesn't answer my question - that is, did the liquid lawn
fertilizer hitting the leaves / stems of the tomato plants cause them
to shrivel?

Based upon what I've seen, some extra nitrogen will tend
to make more foliage, more leaves. I'm no where an
expert though... and it really is going to depend upon how
much hit the leaves and how much went into the soil that
covers the roots. I've noticed that tomato plants planted
into the ground have roots that spread out... this is based
upon a tomato plant I've taken out of a pot that was
heavily fertilized with nitrogen, the roots were packed
against the walls of the pot. The leaves did start curling
up while inside the pot. So I washed the roots trying to
get rid of the excess fertilization, and I replanted it into
the ground. It did pretty well for about a month after
the transplant, then I left for about 10 days and I think
the heat pretty much killed it... well it's still alive, but
it has no leaves on it. All the leaves grow to be small
leaves and then turn turn brown and fall off.

--
Jim Carlock
http://www.votetoimpeach.org/
http://www.911forthetruth.com/
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This summer so far we've been cooler than normal (great-lakes area).
And wetter than normal. Nothing is going dormant around here. Last
summer I watered like crazy in July and August. Not this summer.

Still doesn't answer my question - that is, did the liquid lawn
fertilizer hitting the leaves / stems of the tomato plants cause them
to shrivel?

Probally not. But next time try liquid bloom-buster and your tomatoes will
love you forever