September To-Do

Vegetables and Herbs Garden

• Plant cool-season vegetable crops now – cabbage, turnips, kale, mustard, spinach, lettuce, broccoli, collards, carrots, and beets. Keep seedlings and transplants well watered and mulched.  (The seeds will need at least 2 weeks more time to grow to maturity now than they did in the spring due to reduced light.)  You can cover fall garden crops later in the month with a floating row cover or cold frame to further extend the harvest period.
• Brassicas all taste better after they have been touched by a frost or two and if covered (even just with leaves), most vegetables will survive the winter to provide an early spring harvest.
• Feed your fall vegetables weekly.  Mary Ellen in Behnkes’ Potomac store recommends Miracle-Gro for Vegetables and goes on to say, “When feeding, it’s fine to wet the plant foliage, but be sure to soak the soil around the plant, too.  It’s easy to mix the powder with water in a watering can, or simply attach the LiquaFeed sprayer right to the end of the garden hose and water as usual.”
• If you continue to feed them weekly, rosemary, thyme, and basil will continue to produce leaves until frost.
• Garlic cloves can be planted up until Thanksgiving for harvest in June.  Choose the largest cloves from the largest heads, plant the cloves root end down, spaced 4-6 inches apart, and cover with 1-2 inches of soil.  Use your own home-grown garlic rather than store-bought, if possible.
• Dig storage potatoes on a cloudy after the plants begin to die back, then let them dry for a few hours before bringing them inside – but don’t wash them!  Store potatoes in a dark, cool location. Sweet potatoes should be harvested the same way, except that it’s best to cure the roots for 10-14 days in a warm, dark location and then store them for the winter in a cool, dry location.
• Harvest your onions, once their tops have withered, by lifting the bulbs and drying them in a warm, dry, sunny location for 10 days. Then store them in a cool, dark, dry place.
• To harvest herbs, remove individual leaves of tarragon, rosemary, basil, sage, etc.  and dry them indoors. Herb leaves are most flavorful right before the plant blooms. Snip foliage in the morning after the dew has dried. To dry herbs for storage, tie the cut stems together and hang them upside down in a dry location. Cover with a paper bag to avoid losing the shattered leaves. Store dried herbs in glass jars away from light and heat. Fresh basil can be processed into pesto or frozen in plastic containers for winter use.

• September is an excellent time to plant or move trees and shrubs – just be sure to keep them watered if there isn’t sufficient rain. (Click here for more about watering new plants.)  But don’t plant when the soil is wet – it ruins the soil structure, making poorly draining clay soils even worse.  (Rain IS great for buying plants – you’ll have the store more or less to yourself with abundant staff.
• Keep shrubs and trees watered through the first hard frost so that they can survive the winter.  Evergreens especially need to go into winter well hydrated.  They’re the plants that rarely wilt, giving us the sign that they need watering.
• Do NOT feed or prune this month – both stimulate new growth, which wouldn’t have time to harden off before it gets really cold, and all that new growth would quickly be killed.  It’s fine, however, to remove dead, damaged, diseased branches; also, suckers and water sprouts.

Perennials and Annuals

• September is also a great time to plant or move perennials.  Just keep them watered if there isn’t regular rain.  BUT, don’t plant when the soil is wet because it ruins the soil structure, making badly draining clay soils even worse.
• It’s also a great month to divide perennials, and large clumping ones with dead centers are definitely due for a little surgery (a cheap steak knife will usually do the job).  Just be sure to keep them well watered if it doesn’t rain.  Peonies especially should be moved or divided now if they need it, not in the spring or summer.
• Remove ratty leaves on perennials that are done (like hostas) but leave the coneflower seeds heads alone until late winter because the birds (especially goldfinches) love them.  More good candidates for leaving the seedheads in place are coreopsis and black-eye susans.  Ornamental grasses can also provide needed cover for over-wintering birds.  Also if you want to encourage self-seeding, leave the seedheads up through this month (e.g., Nicotiana, alyssum).
• Larry Hurley’s perennial advice for September:  “Some perennials will begin to go dormant as fall approaches. It’s not unusual for hostas to begin to take on a golden color, and for summer blooming plants to go out of flower. Look for fall-blooming perennials at Behnke’s: consider Asters, Tricyrtis (or “toad lilies”), and Japanese Anemones and Solidago, the goldenrods. One of the best asters for butterflies, assuming you have a sunny area that drains well, is Aster oblongifolius, the fragrant aster. Cultivars include ‘Raydon’s Favorite’ and the shorter ‘October Skies’. Shortness is relative as they both tend to lay down… Blue flowers in October feed migrating butterflies when not much else is in bloom. My favorite Goldenrod is Solidago rugosa ‘Fireworks’, which is (of course) yellow, and looks like a cascade of fireworks with arching and cascading flowers.”

Annuals

• Plant hardy mums now so they will become well established prior to cool weather.
• Pansies, violas, ornamental cabbage and kale can also be planted this month.  More great plants for fall color include sweet alyssum and dusty miller.
• Continue to fertilize your annuals this month – a liquid fertilizer gives them the boost they need and is fast-acting.  Alex Dencker at our Potomac store likes Espoma’s Gro Tone.  It’s a fish protein-based liquid fertilizer that doesn’t smell as bad as most fish-based products.  He says “It’ll maximize your annuals’ lifespan and increase their vibrancy and color.”

Bulbs

• Buy spring-blooming bulbs as soon as they’re in the stores for the best selection.  Select healthy, disease-free bulbs.
• Plant spring-flowering bulbs this month or next – except for tulips, which should be planted from mid-October through November.  Add bone meal or bulb fertilizer into the planting hole as you prepare the soil.

• September is the ideal month to bring houseplants indoors after they’ve spent the summer on your deck or patio, rather than later in the fall when the difference between outdoor and indoor temperatures would stress them unduly.  Treat houseplants with horticultural oil and neem oil to control aphids, mites, mealy bugs and scale.