Planting, watering, fertilizing, et al:
Fertilizing NOT recommended – Grasses adapt to a wide range of soils, and over-fertilizing may actually make them flop or reduce flowering. If you see worms while digging the hole, the soil is healthy enough. Adding some simple organic compost (even last year’s leaves or grass clippings) is often beneficial, but is not vital unless soil is very sandy or heavy clay. Avoid chemical fertilizers and manure – they’re often too much. We get our fastest growth and maximum size planting in soil that is simply heavily laced with last fall's leaves, even if they're only partially broken down at planting. (I've often just raked up newly-fallen leaves and put them in the hole with soil around the root ball.)
Watering – Grasses are very drought-tolerant once established, but they do need a half to a full bucket of water (depending on size and temperature) every second or third day until established, and then at least weekly into fall. A good rule of thumb is to picture the size of the root ball that was planted, and apply enough water (dead-center) to fill a container of equal volume.
Late summer planting calls for more frequent watering to support root re-growth and hydration in preparation for winter. One good soak is always better than several small ones, because shallow watering encourages surface roots, reducing drought-tolerance. Water is best applied dead center in the plant, with a gentle, showerhead style nozzle, one plant at a time. Sprinkler systems or soaker hoses aren’t enough the first year for anything larger than a half-bucket root ball, unless they’re on for at least two hours.
Dark gold or burgundy tones in the foliage are normal after transplanting – indicating normal shock. The discolored foliage can be trimmed away, but it will usually green up again if watering is maintained. If foliage becomes parched brown and curly, it’s a clear sign to water longer and/or more often.
Once a sun-loving grass has wintered over in the ground, it will not likely need any supplemental water to survive, though some water in severely dry seasons will help cosmetically. Over-watering a mature grass can cause reduced flowering and limp stems in many varieties.
Spring Cutback - Most grasses should be cut down in spring to 4-8 ”+/- (exact length not critical) before new growth gets up very far, so the old growth doesn’t detract from the new. Most people wait until spring so they can enjoy the winter look of the grasses, but cutback can be done in the fall without harm. The best hand tool is a sharp, fully serrated “rescue”-type knife, such as Cold Steel's "Land & Sea Rescue" knife, but a few varieties of grasses with really large-diameter stalks may be easier with a pruner or fine-tooth saw. Be sure to wear gloves, as the cut stems puncture skin easily.
If you have many to do, a good powered hedge trimmer (or brush-cutter blade or heavy-duty weedwhacker) is very advisable.
Whether by hand or machine, Miscanthus and other heavy-stemmed varieties are usually easier to cut back at 8"+/-, simply because they're a little smaller in diameter up there.
If you're planning to re-mulch that area, and are using a powered cutter, make multiple passes through the stalks, starting at the top, in 3-4" increments, and just let the cut pieces fall where they may. Then cover them with a light layer of new bark mulch. This avoids the need for you to deal with long stalks, gives you a light layer of perfectly good grass mulch under your bark, and as it breaks down over the year it will provide all the nutrients your grasses need. (When your grasses get really large, you may need to remove some of the cut drop and add it to your compost pile, but the basic logic still applies.)
It's also very helpful to clean out the cut drop from the top of the plant ("dethatch"), to let the light and heat in to the new stems. You can do this by pulling all the dead drop out with a gloved hand, but sliding the tines of a pitch fork through at ground level and lifting up can clear most of the debris with very little effort.
Choosing Grasses for Your Area - Most published zone ratings for grasses tend to be somewhat conservative, especially with Miscanthus varieties. If you really love a grass that's rated one zone warmer than where you are, it's probably worth trying at least one anyway. This is especially true now, when winters have been running warmer than in recent decades, to such an extent that the USDA hardiness zone maps are being redone. There are areas in New England designated as Zone 4 on the current USDA map that some growers insist are now truly Zone 6 - a full two zone difference.
The farther north you are - and presumably the shorter your "hot" growing season - the more you should be looking for early bloomers like the Switch Grasses, and Miscanthus varieties like Malepartus and Purpurascens (Flame Grass). Though only a few weeks earlier than some others, that's a few more weeks to enjoy your blooms, especially in cooler years. (See also next paragraph - Sun vs. Shade)
Sun vs. Shade - "It's not the light - it's the heat." Many popular grasses (including Miscanthus, Switch and Fountain) are "heat-growers." Their metabolism runs best from 80 to 95 degrees, producing faster growth and earlier blooming. Just like roasting a turkey, it takes a certain number of hours/weeks at the right temperature to grow a grass to size and make it bloom. And just like turning down the oven, shade slows things up. However, most grasses can tolerate fair amounts of shade, though they may be shorter and will bloom later than those in full sun. Stems may also be somewhat more lax (i.e. less rigidly upright) in partial shade, as can happen even in full sun in unusually cool summers. (The latest fall bloomers, like Gracillimus and Autumn Light, may not open fully or at all in shadier areas - or in some years in more northern areas with shorter "hot" growing seasons, meaning weeks with multiple days over 85 degrees F.)
When to plant or divide – Grasses can be planted and/or divided from early spring into early autumn, with some extra precautions as fall approaches. Like all plants, if there’s significant root loss from transplanting or dividing, grasses need serious water and enough warm days to sufficiently reestablish themselves to survive their first winter in a new spot. After about August 15, divisions (which unavoidably have severe root damage) become somewhat risky, but for most species, whole plants with reasonably intact root balls can be confidently planted even into late October, if very well watered into November. Heavier than normal mulching (4-5”) is very advisable around grasses planted after August, until after that first winter.
Dividing tips – Many books say you can divide grasses with a spade, but many grasses are tough enough that we recommend placing a hatchet or axe head where you want to divide and driving the head through with a heavy hammer or hand maul. (Safer and more accurate than just swinging away.) For really large grasses, a wrecking bar with a chisel tip can be very helpful making deep cuts, and can be pounded with a hammer, too.
Even better, if you have one or can rent one, is a Sawzall with a 12" demolition blade. For a really big grass, it's well worth the half-day rental rate for the Sawzall - especially if you're not a 20-something football player. A chainsaw will do the job, but it will kill a chain pretty quickly, and also tends to throw a lot of debris back in your face. Be sure to wear good eye-protection if you go with the chainsaw.
Dividing is easiest in spring before the foliage gets too tall, but it can be done into late summer, with regular, deep watering of the new divisions until heavy frost.
It’s easier to divide larger plants before digging them out. The ground holds them still for you, and it’s easier to get the divisions out than one big clump. If you’re leaving part of the original plant in place, dividing in the ground also allows you to leave one side of the root ball completely undisturbed, which will greatly speed recovery.
Like other perennials, older grasses eventually lose vigor in the center. Most books suggest dividing the grass to remove the center, and then replanting one of the divisions. This is a lot of work, and your big, beautiful grass becomes much smaller. A better way which takes much less effort is to “core” the plant in place - just like an apple or pineapple. The best tool is a Sawzall or other reciprocating saw with a 12" "nailed wood" blade. Otherwise use an axe or chisel-tip wrecking bar to chop up the dead center until you can remove the dead stuff by hand. Then just fill the center cavity with soil and water the plant through the season as you would a new division, right into fall. Besides taking about 1/5 the effort, this preserves the original diameter of the plant and it will grow back quickly into the center, especially since the outer perimeter roots are not cut in the process. In subsequent years, use the Sawzall or other tools to make lesser stimulating cuts in the plant's center, and it will reinvigorate every year so that it will be a long while before you need to core it again - if ever.
***WillowMist coring method (click here)
Embedded Weeds & Trimming – Feel free to trim away broken stems or unsightly foliage on an established grass at any time. Even the most radical cutback won’t kill an established grass. (It’ll stimulate it.) Likewise, if a weed is so embedded in the crown of your grass that you can’t pull it without breaking, have no qualms about driving a knife or axe blade deeply into the crown, and spread it open to give you access to the weed’s roots. Grasses are more than tough enough to recover from this – and will likely produce a burst of healthy new growth in response. (Remember that weeds are only a cosmetic problem. You don’t HAVE to eliminate them.)
Spacing – Most grasses eventually reach 18-30”+/- at the base (often 12” the first year), with foliage spans of at least 3 ft. Remembering that they can be moved and/or divided as they get larger, mature grasses will eventually want to be 3-4 feet apart, center-to-center, to minimize intertwining of foliage between neighboring plants.
Mulch – Any bark or similar mulch is good to suppress weeds, as well as hold moisture and soil in place, and will provide a slow but steady supply of nutrients. Plastic weed barriers are OK, but should be kept at least 1.5” away from the plant to allow new stems to emerge around the base - unless you want to deliberately restrain size.
Cut and dried grasses – The blooms of most grasses can be cut and brought inside with great ease. Placed in water, they will hold their look for days or weeks, depending on variety. After that, simply discard the water, and they will dry beautifully, upright in the container, taking on their natural winter look. Alternatively, you can simply cut and tie a bundle and just stand it in a corner, where it will take on its dried look in a day or two, and last years.