Leave saucers of water out at different levels for insects, birds, toads and other creatures, especially if your space and the surrounding landscape is largely hard-surfaced and lacking in water sources for wildlife. As for actually watering your plants, if they're native and in the ground (pots are another matter) they are adapted to local conditions and under normal circumstances will survive just fine without you. So don't waste your time and the Earth's resources.
Cut the spent flowers off and your plants will flower for a longer time. If you let them go to seed, they figure, job done and time to get into the next stage, which is storing energy to survive winter.
In sharp contradistinction, weeds should not be allowed to go to seed as that's just making more work in the future. Get them before they have seeds on them. Pull and lay the weeds on their side to decompose, return nutrients to the soil, and turn into mulch.
This moderates soil temperatures, conserves moisture and discourages weeds. The best mulch is leaf mould (well-rotted leaves from a previous year). Compost is good although if it's your own (to be preferred) it may contain weed seeds, but that's a small price to pay for the most balanced nutrition you can provide. Mulching is especially important for trees, so come fall, don't rake your leaves away, they have nutrients your trees need and accumulated leaf litter provides protection against deep frost.
As the saying goes, 'If something is not eating your plants, then your garden is not part of the ecosystem.' If insects are chewing up your ornamentals, consider that we need insects to survive the environmental crisis that's upon us. Native plants recover from most insect attacks. If they're competing for your veggies, try row cover. You weren’t thinking of using pesticides, were you? Larger competitors like rabbits and deer can be discouraged by physical barriers and planting strategies (plant what they won't like). In the end, tolerance will lead to understanding and compromise.From Audobon: Why Native Plants re better for Birds and People
We close in August for a reason. This is the time to enjoy the benefit of your work. Get acquainted with the creatures for whom your space in the outdoors is home. Watch, listen, touch, taste, smell and enjoy.
There's always next year. Read some books - Arboretum America
by Diana Beresford-Kroeger, 100 Easy-to-Grow Native Plants
by Lorraine Johnson, Growing Trees from Seed
by Henry Kock, Gaia's Garden
by Toby Hemenway and Pollinators of Native Plants
by Heather Holm are among my go-to favourites - and grow gardens in your mind.