October Gardening Taks from The Webster Arboretum

October is the gardener’s final curtain call. As beds empty and plants die back, take time to review this year’s successes and challenges and plan next year’s garden. Write down your observations now, while they are fresh. Fall is also an excellent time to plant perennials, ornamental grasses, shrubs, trees, and more, so look for end-of-season sales at garden centers and nurseries.

In our area, plant evergreens by early October. Deciduous trees and shrubs can go in later, ideally by the end of November and no later than December 1, as long as the ground has not frozen.

Dig up herbs such as rosemary, parsley, and chives. Pot them for a sunny windowsill, or dry and store them for winter use.

Plant Garlic & Shallots

Plant garlic outdoors between October and November, around the same time as spring-flowering bulbs. Fall planting gives garlic time to establish strong roots and supports better clove formation. Because garlic needs a period of cold dormancy to thrive, fall planting works best where winter temperatures remain below 40°F.

Garlic and shallots grow best in soil rich in organic matter, so work in plenty of compost or aged manure before planting. For larger bulbs, consider adding bonemeal or another potassium-rich organic fertilizer. Apply a second round of fertilizer in early spring for an additional boost.

Plant garlic in nutrient-rich, well-draining soil where it will receive 6 to 8 hours of full sun each day. Avoid heavy clay or waterlogged soil; in those conditions, use raised beds or containers at least 8 to 10 inches deep. Water thoroughly after planting, then leave the garlic undisturbed until spring.

Divide Perennials as Needed

How can you tell when perennials need dividing? Common signs include smaller blooms, a bare center, or stems that require staking. You can also divide healthy plants to spread them to other parts of the garden. Plan their new locations now so each division has a suitable place.

As a general rule, divide spring- and summer-blooming perennials in late summer or early fall, and fall-blooming perennials in spring. Transplant divisions immediately and keep them moist to prevent the roots from drying out.

Divide ornamental grasses while they are dormant, before new shoots emerge in spring.

Plant Flower Bulbs

Plant spring-flowering bulbs in fall while the soil is still workable and mark their locations to avoid stepping on new shoots next spring. Plant any time before the ground freezes, typically 4 to 8 weeks after the first frost. In areas with heavy deer pressure, choose daffodils, crocuses, irises, or alliums instead of tulips.

Unlike seeds, bulbs should be planted deeply—about two to three times the bulb’s height. Place each bulb with the rounded end down and the pointed end up, cover it with soil, and water thoroughly to encourage root growth.

Sow Perennial Flower Seeds

Many perennial wildflowers produce seeds that remain dormant until they experience a period of cool, moist conditions called stratification. You can stratify the seeds yourself or sow them in fall and let winter’s freeze-thaw cycles and changing soil moisture prepare them to germinate.

Prepare the planting area now but wait to sow your seeds until temperatures are too cool for seeds to germinate before winter. In our region, the ideal outdoor sowing window is typically mid-October through December. Perennials such as Echinacea, Wild Bergamot, Milkweeds, and Blazing Star respond well to fall or winter sowing, as do some annuals—especially Poppies.

Nurture Your Soil

Fall is an ideal time to test garden soil and make amendments based on the results. A healthy soil ecosystem provides plants with easy access to air, water, and nutrients.  Understanding your soil is the first step to creating an optimum soil ecosystem.   

Soil is a living ecosystem; a large community of organisms linked together through nutrient cycles and energy flows. Every teaspoon of soil is home to billions of microorganisms—bacteria, fungi, nematodes, insects, and earthworms that play important roles.  Without these creatures, soil is effectively just inert "dirt" or crushed rock, lacking the living biological processes needed to support plant life. 

Spread finished compost over empty vegetable and flower beds, but avoid fertilizers not recommended by a soil test. Cover bare soil with shredded leaves, clean straw, or a cover crop to reduce erosion, suppress winter weeds, and add organic matter as the material decomposes.

Don’t forget the lawn! 

You’ve hopefully been mowing your grass to a height of 3.5 to 4 inches this summer, as taller grass shades out weed seeds, keeps soil cooler, promotes deep root growth, and increases drought tolerance. Now it’s time to think about managing fall leaves and the last mowing. Chopping up and leaving fall leaves on your lawn will provide organic matter that will benefit the grass if there aren’t so many leaves that they smother it. (Excess leaves can be piled and will compost without any help from you)!

Your last mowing for the season should leave the grass at about 2 to 2.5 inches tall. This height provides enough blade for growth in the spring and decreases chance of fungal disease that is more common with grasses left at a taller height over the winter. When reducing grass height for winter, never remove more than 1/3 of the height at each mowing; doing so can stress the grass plant.