The dry weather through much of winter has allowed energetic gardeners to get out and complete most of the obvious gardening tasks, but there's still plenty to do in March. A few final pruning jobs put the wrap on last year's growing season, and then we get to look forward by preventing spring weeds, protecting against snails and slugs, and dividing grasses and perennials so they can perform their best in years to come. Here's what to do in March.
Prune frost-tender plants. Many plants such as Angel's trumpet (Brugmansia or Datura), Mexican bush sage (Salvia leucantha), ornamental banana trees (Musa), citrus of all kinds, and some types of fuchsia either turned to mush or developed sad burnt-looking foliage in response to the cold stretches this winter. If you left the old foliage on to protect the buds or other parts of the plant that may not have frozen, that was smart! But by late March, I find that most of our frosty nights carry less power than the ones in December and January, and it's usually safe to prune these frost-tender plants to remove the damaged stems and foliage and give the plants a clean slate from which to emerge.
Regenerate overgrown rhododendrons. While most rhododendrons are perfectly happy with only periodic pruning to improve shape or remove dead wood, sometimes even the most beautiful rhody can overgrow its space. When this happens, most varieties can tolerate being pruned to nothing but bare branches in order to bring the plant down to a more appropriate size. Rhododendrons come back from pruning to bare wood because they have what's called latent buds: whorls of pinhead-sized green or brown buds which stick out through the bark and push out new growth when the rhododendron is pruned. Rhodies produce new growth most effectively during and just after that spring bloom, so the best time to prune is either before they flower or just as blossoms are starting to fade.
Topdress garden beds with wood mulch. If winter rains have broken down or washed away your mulch, this is your best opportunity to reapply before everything begins growing so exuberantly that you can no longer navigate your wheelbarrow through the beds. Wood mulch, of course, is the most effective technique out there for reducing the amount of weeds that come up in your garden beds, because it works in two ways: by smothering any existing weed seeds that are lying dormant under the soil surface, and by creating an inhospitable sprouting environment for any new weed seeds that may blow in. The caveat is that you need to use at least three inches of mulch and lay it down over a smooth soil surface in order to get the best benefits, and you can't use mulch in areas where you have reseeding annuals or biennials.
Apply corn gluten to lawns to prevent weeds. If you are trying to avoid using chemical herbicides such as 2,4-D, yet still want a lawn free of weeds, now's the time to use a corn gluten product as a preventive or pre-emergent herbicide to prevent new weeds from coming up this year. While corn gluten won't kill any weeds that are already in your lawn, it forms an invisible barrier which prevents any new seeds from sprouting. That said, don't use corn gluten if you intend to add new grass seed to your lawn over the next six months, as it isn't picky about which seeds it blocks from sprouting. For existing weeds with a taproot like dandelion and dock, a standing weeder such as the Fiskars UpRoot weeder works like a charm.
Take protective measures against snails and slugs. The easiest organic method for protecting susceptible plants such as hostas, dahlias, and vegetable starts from damage is to use organic iron phosphate bait. Make sure you scatter it around those plants you want to protect, as well as near any areas where the slugs and snails may be hiding, such as within the foliage of lily of the Nile (Agapanthus), gold dust plant (Aucuba), or in any areas of the garden that have piles of debris or stacked wood for them to take shelter. Never place the bait in piles, because even though it is safe for pets when used as directed, any animal can get iron poisoning if they eat enough of it.
Divide late-blooming perennials and ornamental grasses. Most varieties of perennial and ornamental grass grow in ever-widening clumps. This is great for a while, but at a certain point they outgrow their space and can even die out in the center if left unmaintained. To prevent this, plan to divide any too-large clumps every three to five years. Start by lifting the plant out of the ground with a sharp shovel. If the plant has fleshy, bulbous roots, tease them apart with your hands and a garden fork until you've divided the plant into three to four smaller plants. If the plant has a more dense, fibrous root system, use the serrated side of your soil knife or an old saw to slice the base of the plant and the root system into sections. Now's the time to divide chrysanthemum and asters, bellflower (Campanula), canna, hardy cranesbill (Geranium), hosta, yarrow, sweet flag (Acorus), Japanese forest grass (Hakonechloa), maiden grass (Miscanthus), and fountain grass (Pennisetum).
Apply John and Bob's Soil Optimizer. The gardening world has its share of snake oil salesman, and having been in the business for so many years, I'm naturally suspicious of any product that claims to improve growth conditions in some vague way. However, after seeing no fewer than four different locals with terrible, horrible, no good, very bad soil growing lush plants that should've been chlorotic or dead and attributing this product to their results, I've come around to being a fan. If your garden isn't doing what you think it should, and you're not entirely sure what's wrong but suspect a problem with the soil, this humic acid treatment helps to make the nutrients in the soil more available to the plants, increases the activity of beneficial microbes and mycorrhizal fungi, and coats the soil particles to naturally aerate the ground. Apply to troubled areas of the garden in spring so the rain can water it in.
Plant potatoes. Seed potatoes have begun arriving in the nurseries. Choose from red, gold, or baking potatoes, or try something different by growing fingerlings or varieties that have purple flesh. To plant, prepare a garden bed by loosening the soil and adding plenty of organic matter such as compost. Avoid using fresh manure, as it can activate the "scab" pathogen which causes a rough texture on the skin. Dig a shallow trench six to eight inches deep, place potatoes a foot apart, and cover the plants with three to four inches of soil. Once the plants reach 10 inches tall, cover the plants' stems by raking soil up and around from both sides. This encourages the plants to produce additional roots, which means more potatoes at harvest time.
Browse the rhododendrons. If you wanted to add a new rhody to your garden, you could in theory look at photographs online, make a responsible decision based on what you have room for in your garden, and call your order into the nursery. However, plant geeks know that the best gardens leave a little room for serendipity, which is to say impulse purchases. And what a perfectly delicious season for impulse purchases it is. From now through the end of May, rhododendrons are blooming in an array of hues from the deepest burgundy to creamy beige, flaming orange, yellow and red, and rich shades of purple. The flower shapes vary too, with drooping trumpets, neatly rounded clusters and cheeky frizzled starbursts covering the plants. If you are still thinking of rhododendrons as having gangly habits, unattractive foliage, and boring flowers in shades of pink, pink and more pink, you really need to check out what's new in the rhododendron world, because modern varieties bear little resemblance to those sorry parking-lot specimens of old.
Genevieve Schmidt is a landscape designer and owns a fine landscape maintenance company in Arcata. She blogs over at www.NorthCoastGardening.com.