One of the misconceptions about gardening is that you should never plant in summer when it’s hot—planting is best done in spring and fall when the weather is cooler. Basically this only applies when transplanting or dividing, which is digging up all or part of a plant that has already established its roots in the ground and moving it to a new location. It’s nearly impossible to dig up an established plant without destroying some of the roots, and if you try to move that plant during summer's heat when it’s top-heavy with growth, the shock can be fatal.
Just because the temperature’s rising doesn’t mean you can’t continue to fill the empty spaces in your garden with plants. You can successfully plant new perennials, annuals and shrubs in the heat of summer as long as the plant has spent the last several months in a container. Any shock from transplanting is essentially eliminated since you didn’t actually dig up the plant. Summer conditions may cause new plantings some stress, but it’s nothing that the following planting techniques and summertime tips can’t overcome.
Finding the right spot
One of the great things about planting in summer is that most plants are in their full flush of growth, which allows you to better visualize the total effect new additions will have on a space.
But good looks and your personal preference aren’t the only things to consider when placing your plant. Anytime a plant goes into the ground you should match the its growth habits to the garden site. This is true in any season, but especially so in summer when rising temperatures, bright sunlight and drying winds can be at their most extreme.
A plant that prefers part shade but tolerates full sun has a better chance of surviving in full sun if it's planted in spring rather than summer. That way the roots have enough time to take hold in the ground before the heat of summer erupts. When planted in full sun on a hot summer day, however, the plant may wilt before it has a chance to situate its roots. In this case, you can still successfully plant in summer by giving the plant what it prefers—a partly shady location. If you're set on putting the plant in a sunny location, another option is to temporary shade the new planting for the first week or so using a light-colored umbrella, shade cloth or other structure that provides some protection from the sun.
Planting particulars
When it comes to actually putting your plant in the ground, a little preparation can go a long way in determining whether a plant thrives or fails. And, when planting during the heat of summer, the time of day you plant can be just as important as how you plant. For best results, always plant on a cloudy day or in the cooler temperatures of the early evening. This will minimize weather-related plant stress and there will be less transpiration loss from the plant's leaves.
The same basic planting steps apply whether you're planting in spring, summer or fall: dig a hole a little deeper and about twice as wide as the plant's root ball; gently work the root ball loose with your hands or a garden fork; put the plant into position and backfill with good soil mixed with a little compost; tamp the soil to stabilize the plant and remove any air pockets; and then water thoroughly. However there is one additional step that is crucial to planting in summer's heat: after digging the hole, fill it with water and let it drain before putting in the plant—especially when dealing with clay soil. This helps to ensure an easier transition for the plant since the hole and surrounding soil are thoroughly moist.
After the fact
Give your plants an advantage over summer's heat by applying a 2- to 3-inch layer of organic mulch—such as compost, shredded leaves, cocoa bean hulls or bark dust—immediately after planting. This will help conserve soil moisture and keep down weeds, which compete for water and nutrients whether your soil is loamy, sandy or clay.
Water new plantings once or twice with a dilute solution of fish emulsion or liquid seaweed to help them quickly settle into their new environment. During the first week or so you may need to water daily or every other day depending on the weather, soil type and the plant's growing requirements. After that it's important to keep the soil slightly moist until the plant becomes established in the garden. For most perennials and shrubs that usually occurs after the first growing season. The key is to water deeply and thoroughly to encourage a deeper root system.
It only takes a little extra attention and a few simple techniques to help new summer plantings thrive. So go ahead and take advantage of summer plant sales and fill in those empty spaces in your yard. The result can't be anything less than beautiful.
What to Plant
Just about anything growing in a container can be planted in summer, though some plants stand up to summer's heat better than others. Here's a list of several tough contenders for summer planting.
Standout shrubs: Barberry, boxwood, bluebeard (Caryopteris spp.), chaste tree (Vitex agnus-castus), clethra, cotoneaster, holly, honeysuckle, hydrangea, Japanese plum yew (Cephalotaxus harringtonia), juniper, rose, santolina, spiraea
Persistent perennials: Japanese anemone, artemisia, aster, catmint, chrysanthemum, coreopsis, daylily, echinacea, geranium, goldenrod, helenium, liatris, ornamental grasses, phlox, plumbago (Ceratostigma plumbaginoides), russian sage (Perovskia spp.), salvia, sedum, verbena, veronica, yarrow
Late-color annuals: Celosia, chrysanthemums, coleus, cosmos, creeping zinnia (Sanvitalia procumbens), dusty miller, dwarf sunflowers, globe amaranth (Gomphrena spp.), impatiens, marigolds, nasturtiums, salvia, scaevola, zinnia
Conquer & Divide
An easy way to find new plants for the empty spaces in your yard is to divide certain perennials that already exist in your garden. As Autumn's cooler nights approach in September, it's a great time to dig in and divide perennials like asters, chrysanthemums, daylilies, iris, liatris, rudbeckias, and ornamental grasses. Divide and replant perennials with vigorous clumps, barren or dead centers, and those whose flowers have become smaller or less abundant.
The steps are basically the same whether the plant grows from rhizomes such as iris, has tuberous roots like daylilies, or are more fibrous like rudbeckia. Simply dig up the plant on a cloudy day, keeping as much of the roots intact as possible. Remove any loose soil so you can easily see the crown and roots, then divide the plant into smaller clumps using a sharp spade or sturdy knife, discarding any dead centers to the compost pile. Each division should have at least two to five vigorous shoots with ample roots attached. Cut back remaining foliage to half the plant's height, then immediately replant the divided pieces into their new location. Any extras can be planted in potting soil in large pots and later given as gifts to friends and family.
