The September clock is ticking, and the next two weeks offer a vital window for yard and garden tasks. September is always an important gardening month as summer transitions to fall, but it’s especially important this year as we help our lawns and landscapes heal from this summer’s heat and drought.

Following is a checklist of tasks that are best completed before September ends.

  • September is the most important month for lawn care as grass plants build their strength, energy and root system for the following year. Apply lawn fertilizer in September so grass has the nutrition it needs, preferably using fertilizer labeled as a fall-type or “winterizer” which has extra nutrients for root growth. Even if you never fertilize your lawn the rest of the year, a September application will greatly improve the lawn’s health, creating a deep root system better able to thrive in adversity.
  • Lawns thinned by drought are recovering with recent moisture and cooler temperatures. Keep the momentum going by fertilizing. If we don’t receive timely fall rains spaced about 7 to 10 days apart, consider giving the lawn one or two irrigations in late September through early October. Apply one inch per irrigation, which is easily measured by a straight-sided soup can located on the lawn. Adequate fall moisture is vital for fertilizer activation and lawn recovery.
  • If drought-damaged lawns aren’t sending up green grass spears every inch or so, consider overseeding. Rake, power rake or core aerate, apply fertilizer, and spread seed. The key to successful growth of grass seed is keeping the surface consistently moist with daily light sprinklings. If seeding, do it now, as the cutoff date is considered Sept. 15-20. Alternatively, lawns can be dormant seeded right before winter sets in.
  • Spot-spray for weeds in September well before frost threatens. Fall is the best time to control weeds, especially hard-to-control types like thistle and creeping Charlie.
  • Fall is a great time to plant trees and shrubs. If planted in September, they’ll have a month or more to produce roots, giving them a head start versus waiting until spring to plant.
  • Give trees a good, slow soaking this fall, since subsoil moisture is still lacking. This is especially important for trees planted within the past seven years or so.
  • Pruning should wait until early next spring. Cell growth of woody plants is slowing down, and pruning cuts don’t seal as rapidly in fall, opening the way for potential winter branch dieback.
  • Plant winter-hardy spring-flowering bulbs like tulips, daffodils and hyacinths as soon as possible. Water well after planting, because the bulbs produce roots yet this fall.

Iris can be dug and divided in August and September. David Samson / The Forum
Iris can be dug and divided in August and September. David Samson / The Forum

  • Bulbs and underground structures that don’t survive winter, like gladiolus, cannas and dahlias should be dug about the time of the first frost, either right before or right after, and readied for winter storage.
  • Plant, divide or relocate peonies, daylilies, true lilies and bleeding hearts in September. August is best for iris, but this month works fine, too.
  • Rhubarb can be divided or moved in September. Portions of the plant can be dug from the perimeter with the mother plant remaining in place, or the entire plant can be dug and divided.
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Some iris cultivars bloom in June and again in September, such as Immortality. David Samson / The Forum
Some iris cultivars bloom in June and again in September, such as Immortality. David Samson / The Forum

  • Garlic, which needs a cold over-wintering treatment, is planted in late September or early October.
  • To develop a new garden spot for next year where lawn exists, skip a mowing, then spray with glyphosate, which is the active ingredient in original Roundup and other brands. Roto-till or spade after about two weeks.
  • Remove vegetable plants that commonly carry diseases, after they’ve finished producing, like tomato, pepper, squash, pumpkin, cucumber and potato vines. Other non-diseased plants can be mowed, mulched, and spaded or roto-tilled into the garden.
  • Bring tropical plants back indoors for winter growth before temperatures dip too far below 50 degrees F, such as hibiscus and mandevilla. Before bringing them in, wash with a gentle stream of water and consider treating with insecticidal soap or similar insecticide. Geraniums can remain outdoors longer, but should be brought in for overwintering before frost threatens.

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Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.