Don’t Make These 9 Late Summer Gardening Mistakes

It’s officially late summer and a time of transition in the weather and the garden. The harvest and blooms continue, with many plants pausing in hot conditions before a final flush as temperatures moderate.

Others, like productive summer annuals, have lived their warm days to the fullest and may be ready for trimming or pulling. Those of us with long growing seasons look forward to harvesting our successional rounds of warm-season crops, while cooler climates are seeding for fall.

There’s still much to enjoy in the late summer garden, with hummingbirds, butterflies, and other pollinators buzzing energetically. It’s a time of therapeutic watering, of savoring the bounty, and of slowing down in the heat while looking ahead to fall planting. The end of the season marks a jumping-off point as we tend to plant and soil health for future productivity.

This month is prime for wrapping up certain tasks to avoid late summer gardening mistakes. Deadheading, adjusting fertilizer schedules, light pruning, and protection against extreme heat set the foundation for a healthy cool season.

Skipping Deadheading

In late summer, it’s possible for many of our favorite blooms to get another round of color as temperatures moderate toward fall. Deadheading now promotes faster reblooming for that final flush. Not only vibrant, the extended flowering supports pollinators and beneficial insects as the seasons transition.

Removing aged blooms redirects the plant’s energy from seed production into further flowering. Stop deadheading by late August or early September to let blooms go to seed in the fall. Let them naturally drop and scatter for next season’s show or collect them for spring planting. They’ll also provide forage for birds and small mammals heading into winter.

Fall-blooming perennials and annuals benefit from a final round of deadheading late in the season before setting seed. Salvia, aster, coreopsis, rudbeckia, zinnia, and marigolds will reflower faster for a fall display with deadheading now. 

Deadhead reblooming roses, too, to encourage another flush. Gardeners mark Labor Day as a good time to stop deadheading roses, or about six to eight weeks before your first anticipated frost date. This gives time for showy rose hips to set and for the shrubs to prepare for winter dormancy.

Clip away dried hydrangeas according to your preference, or leave them on the stem. If clipping, do so now to avoid interfering with bud set for those that bloom on old wood.

Cutback

While it’s not the time for heavy pruning, late summer cutback revives some perennials and annuals after a long growing season. For many, trimming promotes a fresh flush of growth and a potential late-season rebloom. Gentle pruning helps manage size, prevent overgrowth, and direct energy to roots as plants prepare for overwintering. 

A light approach to cutback this time of year targets deadheading, light shaping, and removing brown, diseased, or dying parts. Removing brown, crispy stems keeps everything healthy, tidy, and fresh.

Trim and harvest herbs regularly to promote a new flush of fall growth and to keep sprawling stems in check. Robust spreaders like mint, organo, and lemon balm may need reining in; use late season as time for shaping for a bushier habit. Remove any blooms to prevent unwanted reseeding. Enjoy the clippings fresh or dry them for use over the winter.

If you’re growing summer squash like yellow, zucchini, and pattypan, pinch the tips of vining stems after enough fruits set. This prevents energy from going into new growth and instead directs it to developing the existing fruits.

Not Protecting Against Hot, Dry Spells

Late summer brings weather fluctuations that include drought conditions and extreme heat. In prolonged hot and dry situations, even the most durable specimens may exhibit signs of stress. Hindered growth, decreased fruiting, wilting, and leaf drop aren’t uncommon at this point in the season.

To avoid the summer gardening mistake of losing a favorite plant to heat stress, keep an eye on those that show yellowing leaves with brown, crispy edges, white patches, and wilting that doesn’t rebound with moisture.

Particularly sensitive selections include those that rely on a lot of moisture to thrive, seedlings, older specimens, those that prefer cool roots, and crops like cucurbits and nightshades.

Protective Measures

A protective shade cover may be the remedy for these late summer gardening mistakes. Shade coverage reduces water loss and lowers internal temperatures while shielding foliage and fruits from direct sun.

Use an umbrella, pop-up canopy, or light shade cloth as protection. Other measures include extra water during summer extremes to keep roots cool and to compensate for increased evaporation.

Use mulch as added protection to regulate soil temperatures and retain moisture. Take care to avoid overfertilizing throughout the season, which creates an excess of quick, weak growth susceptible to sunburn and defoliation. Avoid pruning during high heat, as removing mature leaves exposes underlying foliage and fruits to direct sun.

Fertilizer Last Call

Late summer is a time of slowing growth for many of our garden performers, and the last time to fertilize those that need it. While most plants, including perennials, don’t require late summer fertilizer, it’s an option for those in lean soils or with chlorotic leaves. It also offers a boost in root development before cold weather and a final show of color from a fall rebloom.

Annuals can take regular fertilizer in late summer until they complete their life cycle. Avoid the common summer gardening mistakes of fertilizing in high heat and applying it too late.

Skip applications during heat waves and dry spells, as drought-stressed specimens won’t respond well to added nutrients. Keep in mind your first anticipated frost date, and allow at least six to eight weeks in advance for nutrients to have time to perform and new growth to harden off.

Tender new stems are susceptible to winter damage, and plants need to direct energy to their roots, rather than producing upper growth, for resiliency during seasonal extremes.

Now is the time to finish fertilizing flowering shrubs like roses and hydrangeas. For roses, opt for a balanced blend of specialized rose fertilizer with phosphorus to promote blooming. Seaweed and alfalfa extracts are low-grade options for ongoing support. Foliar feeds, too, can promote a fall flush of flowers for reblooming types.

Slow-release fertilizers distribute nutrients gradually over about two months. Standard granulars break down in about one month, while liquid feeds absorb quickly to spur growth.

Planting Too Late or Too Early

Late summer is prime for cool-season planning, seed sourcing, and sowing initial crops. If you’re still in the throes of heat waves, hold off on direct-sowing cool-season varieties until milder conditions, or start seeds indoors for transplanting later. August seeding includes collards, mustards, kale, radishes, peas, and turnips.

Gaging when to plant in the fall relates to our growing zone, the first anticipated frost date, the length of time it takes our selections to mature, and their frost hardiness. For frost-sensitive crops, we’ll need to harvest before frost to enjoy a full yield.

First Frost Date

Fall’s first anticipated frost date is an estimate that provides a scope of when heavy frost is likely. It doesn’t account for microclimate or specific site conditions, but it is valuable in determining when to sow.

Some cool-season selections perform best in cool conditions leading up to frost, and frost-tolerant crops even sweeten with a freeze. Crop covers or a cold frame extend the season in cold climates, whether in the ground or raised beds.

Days to Maturity

“Days to maturity” measures the length of time it takes the crop to produce mature fruits or vegetables. The seed packet or varietal information lists the number of days to harvest. Use the days to maturity in coordination with the first frost date to determine when to start seeds. 

Count the number of days backward from the frost date (or ask Google to). If you live in zone 8, for example, and your frost is in late November, crops that take 60 days to mature benefit from a late August or early September sowing. 

The days to maturity are a guide based on optimal growing conditions. Add a week or two buffer to account for seasonal fluctuations. Add this buffer to the days to maturity and count backward from the first frost date for sowing.

Not Adjusting Turf Protocols

By late summer, grass may show signs of wear and tear. It’s also peak time for insect, disease, water, and direct sun damage. Continue with supplemental irrigation during dry spells, aiming for an inch or two of water per week. Water deeply, rather than frequently, to promote long roots that increase resiliency across the seasons.

August marks the last chance to fertilize warm-season grasses in zones 7 and above. A final round of nitrogen and potassium-rich fertilizer adds enrichment before winter dormancy. Stop fertilizing by mid-month, or about six to eight weeks before the anticipated first frost, to prevent new growth.

If you live in a frost-free climate where grass stays green all year, go ahead and fertilize with a slow-release granular for extended seasonal nourishment. Wait to fertilize cool-season turf until September or October for lush blades. Cool grasses develop roots in autumn to store nutrients for successful overwintering.

Continue mowing regularly, but raise the mower blade to maintain a height of about three inches (never removing more than ⅓ of the blade at a time). This keeps the blades lush while protecting tender leaves against sunburn.

Seeding and Patching

Sow grass seed in late summer and fall to infill trouble spots or refresh the lawn.

Mild air and soil temperatures of late summer and early fall, coupled with regular seasonal moisture, promote healthy growth.

In zones 7 and warmer, sow warm-season grasses from March through September, avoiding hot and dry spells. Optimal soil temperatures for germination are between 65 and 70°F (18-21°C), and seedlings rely on warm conditions and regular moisture to develop. 

In zones 6 and colder, sow cool-season grasses in mid-August through mid-October. Seeds need cool air and soil temperatures and regular water to sprout. The optimal soil temperature range is 50 to 60°F (10-16°C). Sow seeds at least 45 days before the anticipated first frost for winter survival.

Consider rethinking vast grassy areas this season by increasing bed space or implementing a turf alternative. Cover crop seeds can intermingle with existing grass. Or, create a plan for adding perennial groundcovers in fall.

Ignoring Pests and Diseases

Hot summer days and nights are particularly favorable to common diseases like rust, blight, and powdery mildew.

The good news is that pest activity often slows in late summer as peak feeding and reproduction slow. Squash vine borer, Japanese beetles, squash bugs, and others show reduced activity. But stress from overly dry or wet conditions of late summer makes plants prone to diseases.

One of the best defenses against the summer gardening mistake of ignoring pests and diseases is to keep beds debris-free. Plant debris harbors pests and diseases, even over the winter, and a cleanup lessens their habitat. Clearing dropped leaves and petals also creates a fresh, clean look for a late-season refresh.

The next defense is maintaining optimal cultural conditions, from watering consistently to avoid fluctuations to increasing air circulation around leaves and stems. Avoid overwatering, which leads to fungal issues like root rot. Prune away overgrowth and thin crowded crowns to reduce damp conditions.

Be on the lookout for bagworms and webworms, which stop feeding and now attach to stems to form webs. Manually remove the bags to limit future populations. Spider mites may be an issue in hot, dry, dusty conditions. Spray leaves and stems with a hose blast to displace sap-sucking pests.

Continue to scout for squash vine borers on cucurbits to prevent future infestations. The larvae (caterpillars feeding on the squash stems’ interior) will stop feeding and exit the plants. They’ll burrow into the soil to overwinter until spring.

Letting Weeds Grow and Reseed

Weeds not only compete with our garden selections for resources like nutrients, moisture, and sunlight, but they also host pests and diseases over the winter. Pulling weeds before they set seed helps reduce future numbers.

If weeds are flowering or seeding now, take care when pulling to limit seed dispersal. Less work next season!

Forgetting to Preserve the Harvest

With the final summer yield of tomatoes, cucumbers, squash, blackberries, and much more rolling in, it can be time-consuming to actually use or preserve our harvest. If we make a point of doing so now, though, we’ll appreciate it in the coming months. Pickling, canning, sauces, and preserves let us savor the season.

An even simpler and quicker way to store is freezing the bounty. Vegetables and fruits freeze for months at a time, ready for adding to winter soups or fresh smoothies. Most will need blanching first to deactivate enzymes for preservation, lasting flavor, and to soften skin. You can freeze them in a big block or with flash freezing, which makes for easy use.

Seed Saving

Don’t forget to collect any seeds in late summer and fall of flowering plants and edible crops,  especially if they’re heirlooms, hard to come by, or from pass-along selections. Collect and store them for planting out in spring, or direct sow those that benefit from cold stratification. Seed saving is cost-effective and helps promote genetic diversity.

While we’re preserving the bounty and collecting seeds, clip and dry blooms for lasting arrangements and potpourris. Edible herbs and flowers like calendula, feverfew, chamomile, and marigolds are ready to dry for teas.

Not Soil Testing

Our last summer gardening mistake to avoid is overlooking soil health. Fall is the best time to add amendments, and a soil test now helps us plan and source materials. Amending in the fall gives soils time to absorb minerals and nutrients before the spring growing season.