For plants, location is everything. Imagine living your whole life standing in one spot, unable to go find water or seek shelter from extreme weather. That spot had better work, and it either does or it doesn't. Newly arrived plants - either sprouted in place or planted - are especially vulnerable, but even established individuals will decline and die if conditions aren't right. In this post I'll go over identifying water and light requirements, and the importance of microsites to planting success.
Wild seedlings live or die depending on where they sprout, but in the garden we have the luxury of situating our plants where they are more likely to thrive. Examine your planting area with a critical eye and keep two things in mind: how much light does the area get, and how much water can it expect?
I divide light requirements for our native species into three basic categories:
Full sun - sunny for most of the day. Some morning or afternoon shade is generally fine. South and west faces of your house are typically quite sunny.
Part shade - dappled shade (under a tall open canopy tree, for example) or sunny with shade during the hottest part of the day (such as the east face of a house).
Full shade - no direct sun, but plenty of indirect light. Beneath fairly open canopy trees, or along north facing walls and fences that are otherwise open. Full shade spots are not sunny, but they aren't dark. If grass struggles there (like beneath a very shady tree), even our shade species might struggle.
Water requirements are similarly divided into three loose categories describing how much water a plant might need after it has been established. All planted individuals need regular water during their first season so their roots can play 'catch up'.
Xeric - water only in drought situations
Low Water - once a week in the hottest part of the summer
Moderate Water - once a week throughout the summer, twice during hottest part
Most people water too frequently but not deeply enough. If you are using a sprinkler, I recommend watering at least an hour per location. This seems like a lot, but it drastically reduces how often you have to water, and encourages your plants to send roots deep into the soil where they are less prone to moisture fluctuations. Each time you water, your focus should be wetting the soil layers well below the plant. The first few times after you water, pick a spot in your watering zone and gently wiggle a shovel back and forth in the soil to expose a depth of at least 6". Is it nice and damp, or is it dry past an inch or two? It needs to be damp all the way down; adjust your watering times accordingly.
Divide your yard or garden into zones depending on water needs. You can then cluster species with similar water needs together, which will make watering much more efficient and enjoyable. Additionally, it will prevent plants with specific water needs from out-competing neighbors with different needs, which keeps your garden composition balanced.
When I was first converting my barren lawn to a native oasis, I planted dogwoods shrubs in one of the hottest parts of the yard. Dogwoods are a streamside plant, and need regular water. But they are also gorgeous, and I could picture them flourishing and flowering and blocking my view of the road. I reasoned that I would just nip in regularly and give them extra water; no sweat.
It turned out to be the opposite of no sweat though, lugging the hose out to its physical extreme while carefully snaking it around other plants completely unrelated to my watering activities. Well, that enthusiasm lasted all of several weeks, and eventually the dogwoods just had to make do with the water allotted to the xeric plants around them (so...pretty much none). It's a mistake I've tried hard to avoid since by clustering like species together.
These are guidelines. Actual water needs will be dictated by the nature of the site, and of course the weather. High temperatures and high winds will cause soil to dry out more quickly. One tactic I use to assess soil moisture is to identify a plant that needs slightly more water than the ones around it, a 'canary in a coal mine'. When your canary starts to look stressed, you know you need to think about watering that zone.
Even within zones, though, there will be variation. Microsites are small areas that have environmental conditions slightly altered from the surrounding area due to the movement of air and water and the buildup of heat. They are often the result of physical characteristics like slope, or the presence of a rock, building, or tree. Here are some common microsites you might find in your yard, and how they might influence plant selection:
Pavement - heat build up but extra water runoff right at the edges, making conditions extreme. Generalists that tolerate a variety of conditions, like yarrow and blanketflower, are good options in spots close to expansive pavement.
Roof eaves/downspouts - extra water during rain events. I have successfully grown streamside shrubs and flowers beneath the eaves of my house with very little supplemental water.
Walls that reflect heat/sun - soil will dry out faster; warmer in early spring and hot in summer. Pick more xeric species for these areas when in full sun.
Rocks - the sunny side absorbs heat, ideal for xeric plants, while the shady side keeps roots cool and prevents evaporation of water from soil (good for plants needing a little more water).
Swales - those annoying puddles in winter mean good spots for plants wanting moderate water.
Sprinkler overspray - if you are going to irrigate a lawn, you should put any sprinkler overspray to good use. Good for plants wanting moderate water (make sure you are watering deeply and not too frequently, which also applies to your lawn itself.)
Afternoon shade - lets you get away with using less water in the hottest parts of summer. Perfect for low water plants that you don't want to water at all except in drought, or for moderate water plants you may have a tendency to forget about due to location.
Clusters - planting individuals close together (in clumps) shades roots and provides wind protection, drastically reducing water use over individuals spaced far apart. Ideally you don't want bare ground (bare ground = weeds!) at any time, but if you're just getting started clustering is an especially good tactic to shelter immature new plants.
Identifying microsites and figuring out how they can expand your planting options is a fulfilling, creative endeavor. You can even build your own by strategically placing medium and large rocks or digging out depressions. Combining them can enhance the effects. For example: digging a depression in a spot that gets a large amount of sprinkler overspray can create a nice spot for wetland species of all kinds.
When in doubt as to whether a plant will like a spot...try it. If it doesn't work out you will have traded the loss for knowledge gained and increased the success rate for all your future plantings. The right place for the right plant concept is about finding or creating opportunity on your landscape. No area is truly barren if there is also a human being to tend to it. Nature itself selects and creates microsites over the course of time in a way that we can emulate. Don't be afraid to experiment; the rewards will benefit you and the living things around you.