Could you use spells without towers in Soulkeep?

Trying to play well in soulkeep came from knowing fiends that you would play against and also from being a good battle player an this with towers and spells as you know spells could help tower in their work but also it could act alone and do more damage to fiends in any wave.

I just tried some spells to see its effect alone and this without any tower close to it as when you use a spell near tower you could say that this effect came from the tower not the spell so using a spell with no tower in its range is very good indicator and couldn't misunderstood the effect of the spell.

I have used stew of doom and I know it is cheap and only used with 5 mana but for me this effect is also good as may use it for low mana levels when I need to save some so using a stew of doom without a tower close to it would make it brilliant and cool for seeing how it could do and its proven that Stew of doom is brilliant against low HP fiends.

Venus Fiendtrap alone can do a good work and could eliminate five fiends whatever their HP and this so pretty cool as it could be used near the gate as most players do and this is very effective to eliminate five fiends that would escape from towers and come to your gate.

So using Venus FiendTrap and stew of Doom is very effective alone and this is with no towers close to them as you could see they could do a good work but best use of them is after towers that for injured fiends that would escape from towers would face these spells and these ones would be amazing for them.