Plants that are already ‘established’ only need to be watered once a week. Newly planted need to be kept watered well... until established.

With your soil being as dry as you say it is, it sounds like you are only surface watering. When you water, make sure to water deeply. The way to insure this is to water well, wait for it to soak in then repeat until you see the water start to pool. Usually takes about three good waterings. It helps if you trace a shallow moat in the soil around the plant. It prevents the water from running off. If in doubt you can always insert a finger deeply into the soil to check the moisture level. You’ll want to keep it slightly moist, and don’t let it dry out completely. Hope this helps.

take a hand trowel.. and dig a few 3 to 6 inch holes... AND FIND OUT ABOUT MOISTURE AT ROOT DEPTH ... and then water accordingly ...

we dont really care about the surface being dry ... the roots arent there ..

water a plant.. when it needs water.. how that all works with your plants.. in your soil.. i your weather.. can be determined by no one but you ... that is why al the WWW info is so confusing ...

in every post.. give us a big city name ... in this case.. it lets us have an idea about what summer will really be like ... in your garden. not mine ...

you should also have a proper mulch.. to reduce weeds .. and reduce surface dryness ... as well as moisture at depth ...

i hope you planted the dwarf lilac with plenty of space.. they are not small plants .. they are smaller that the giant momma.. but they do not remain the babe you most likely planted ...

in the extreme ... you can note the date .. and not water until the first sign of wilting ... and then water .. and then you have a bottom line as to how long it takes for water at root level to disappear ...

if your soil drains properly... you can probably not overwater ... you can figure that out if you do a garden perk test ... if you have poor draining soil.. start a new post ...

ken

https://duckduckgo.com/?t=ffcm&q=garden+perk+test&iax=videos&ia=videos

ps: you plant in the soil.. mother earth.. you fill pots with media ... and what you have all over you and the house after playing in either is dirt ... when you start to understand that mother earth is not dirt .. then you are moving toward the knowledge you need to water properly ...