This weekend in the park

What to do after the harsh summer heat

Plants damaged by summer heat and dryness — including the post-Labor Day blast — should begin to recover as temperatures cool in the coming weeks.

Young plants with sparse roots are particularly vulnerable to damage from hot, dry summers, especially if the gardener is spasmodic with watering.

But even mature plants can look bad this time of year. This is because the main summer survival tactic of trees, shrubs and even many perennials is to fold and even shed their leaves as a means of conserving moisture. Leaves are the main way plants lose moisture.

Don’t despair too much about plants with brown-edged leaves or bare branches. As long as the roots are healthy, most plants should return to their natural state.

One thing you can do to help is to keep the ground constantly moist until it freezes. This should be easier in the fall with lower water demand and (usually) higher rainfall.

Moist soil in the fall aids root growth and helps plants recover from summer stresses.

It also prevents plants from going into winter already dry and stressed, which is a particular threat to evergreens and especially broadleaf evergreens, such as rhododendrons, azaleas, holly, cherry laurel, nandina, and boxwood. (Evergreen plants continue to lose moisture in the winter through their needles and leaves while frozen ground can prevent them from absorbing new moisture through the roots.)

Bottom line: Don’t put the hose away too early. We can experience droughts in September and October.

You may see some woody perennials and perennials pushing out new growth in the coming weeks. This is a good sign, but don’t expect spring fullness since plant growth naturally slows at this time of year as day lengths shorten and temperatures cool.

As plants begin to gradually slide into winter dormancy in the coming weeks, this is also why most gardeners advise against fertilizing in the fall — at least with fast-acting, high-nitrogen products.

A light layer of compost is usually fine, but otherwise, fertilize only if a soil test indicates a need. Otherwise, late winter and early spring are the best times to fertilize.

  • Read more about whether or not fertilizing in the fall is a good idea in this Garden Professors blog post

Another post no What needs to be done now is to prune the trees, shrubs and greenery.

First, those bare branches probably aren’t dead, so if you remove them, you’re probably removing perfectly healthy wood that will naturally leaf out next spring (if not this fall yet).

Second, pruning woody plants now will open wounds that increase moisture loss from the plants. For trees, shrubs and evergreens that are stressed and thirsty after a hot, dry summer, this is the last thing they need. Skip the shears, and let the plant’s energy go to growing roots and returning leaves, not to healing wounds.

Third, pruning in the fall can stimulate new growth to replace lost tissue. This is counterproductive to slowing the plants’ natural growth in the fall and may produce tender young shoots and shoots that only freeze to death in the first really cold snap anyway.

As for the flowers, not only were they adapted to the same hot, dry conditions, but they may also have suffered from insects, diseases, or raids by rabbits, groundhogs, and deer.

Most perennials should bounce back and grow normally next spring. In the meantime, it’s a good idea to uproot or cut off any dead or severely damaged leaves and soak the plants well if the soil is dry.

You may also be able to get a second wind of some of your annuals before the first frost of the fall ends.

Some annuals He prefers The weather is cold and they will rebound when the weather cools, especially if you give them a light pruning, a dose of fertilizer, and a good soak.

Among those that often bloom late in the season are alyssums, African daisies (Bony), snapdragon, verbena, diaccia, nemesia, lobelia, and pansies.

You can also try a pruning/fertilizing/watering routine on any other sad-looking annuals, but if they don’t rebound within a couple of weeks, consider pulling them out and replacing them with new fall color.

Garden centers are full of cool-season annuals like pansies, violas, ornamental kale, and ornamental cabbage this time of year, not to mention other fall ornamentals, including mums, golden roses, asters, ornamental peppers, and herbs with colorful leaves (sage, thyme, oregano, etc.). And little pumpkins.

In the vegetable garden, continue harvesting as your summer-planted crops mature (carrots, beets, beans, etc.) and replace the empty space with cold-tolerant vegetables, such as lettuce, spinach and mesclun.

These fast-maturing crops still have time to mature before really cold weather ends their season in November or later.

Early fall is a good time to plant most new plants, especially those that add instant fall color, like this rose mother.

Really fall He is Good for farming (most things)

September through mid-October is usually one of the two best time frames in Pennsylvania for planting almost all trees, shrubs, perennial flowers and evergreens. (Early to mid-spring is the other.)

Eight reasons why:

1.) Soil temperatures are warm enough to support good root growth.

2.) Shorter days, less intense sunlight, and cooler temperatures mean less stress (“transplant shock”) for plants being pushed out of their cozy pots and into the untamed ground.

3.) Newly planted plants lose less moisture through their leaves in the fall than in the summer, reducing water demand as the new plants acclimate.

4.) Rainfall typically increases starting in the summer, reducing the hose power required by new plantings.

5.) Plants planted in the fall will have two growing seasons under their belts instead of one (now and next spring) before facing the prospect of a harsh, hot, dry summer.

6.) The bugs are mostly gone.

7.) A lot of plants are going on sale from now on.

8.) It is more pleasant for a gardener to be out digging in September than in oven conditions in July and August.

Before digging a new bed (especially when using power equipment), find out where buried utility lines are located.

Gas and electrical lines are usually deeper than the depth of a shovel or plow, but cable and computer lines may be only a few inches below.

Call Pennsylvania One Call at 811 or 800-242-1776 to schedule lines. Or visit the website It’s a free service for Pennsylvania homeowners who do their own work.

Call utilities directly that are not covered by the Pennsylvania One Call network.

Keep the soil around fall-planted plants constantly moist until the ground freezes, and aim to finish your planting by the end of October. After that, the soil starts to get cold enough most years that root growth slows.

Research has shown that plants establish themselves best when they have at least six weeks to “take root” before the ground freezes.

Only a few species prefer to be planted in spring rather than fall. These are mostly plants that are hardy or susceptible to winter windburn, such as crape myrtle, cherry laurel, nandina, southern magnolia, camellia, variegated roses, mahonia, and vallei (Osmanthus), Italian Blue Cypress, and Vitex.

Early fall is also a good time to move most plants that you realize are in the wrong place.

Planting mistakes

Early fall is also a good time frame to move plants that you realize are in the wrong place.

Most plants transplant better than you might think, especially if you do this work within a year or two of the original planting. (Newer plants move more easily than larger, mature plants that have established themselves for years.)

It is possible to move a large, mature plant, but it is much more difficult and less efficient. This is because you will cause more damage to the roots when you dig up a plant with an established root system.

September and October are typically the best planting months of the year for the same reasons they are suitable for planting.

As with everything related to gardening, there are exceptions.

It is best not to move plants when they are in mid-flowering. This means it’s best to wait until the other good planting window — the end of March through April — to transplant fare like mums, asters, sedums, caryopteris, roses, and butterfly bush (sterile varieties).

Hardy plants also survive the move better in the spring when their first challenge isn’t a sudden freeze in October. These are generally the same plants you would prefer to plant in the spring rather than the fall, i.e. the above-mentioned list of crape myrtle, cherry laurel, nandina, etc.

A third exception is any plant that has suffered dieback, severe wilting, or leaf scorch during the summer. It is better to keep the ground moist and allow the roots to recover than to add new stress to move. Early next spring would be better timing.

Seasoned plant operators have a few other transplanting tricks up their soil-soaked sleeves.

The first is to make sure the plants are well hydrated before any movement.

If the soil is not moist, soak the ground well the day before digging.

It is also best to transplant later in the day when the transplanted plant has had a few hours to adapt overnight.

Once the plants reach their new home, water well about twice a week for the first six weeks (less if rain cooperates) and then once a week during the first full year.

Basically, treat the transplanted plant as a new plant in terms of water.

  • Read George’s post on how to overcome ‘transplant phobia’
  • More advice on “when to do what”: GeorgePennsylvania gardening month after month” book

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