By Melinda Heigel, NC State Extension Master GardenerSM volunteer of Durham County
With temperatures increasing and perennials waking up from their long seasonal slumber, summer will be quickly upon us. Summer gardening in Durham County presents both challenges and opportunities in the home landscape. Our summer brings the challenges of high heat and humidity, strong sun, and dry weather.
The good news is we live in a region (USDA hardiness Zone 8a) that allows us to grow a wide variety of ornamental plants and vegetables. And despite our constant bemoaning about clay soils, they are often quite rich in nutrients and retain needed moisture.
Probably one of the toughest things gardeners face when the mercury rises is ensuring plants have adequate moisture. As we all know, water is an important resource, so how can you maintain landscapes by using water wisely and keep plants healthy? Here are some strategies you can employ to ensure proper moisture and sustainability.1
Proper Irrigation (There really are better ways to water)
Know When to Water
First, newly-installed plants need more consistent water, sometimes daily, during their establishment period, usually during the first year. Once plants develop root systems, they are better able to tap into moisture already in the surrounding soil. With established plants, did you know that watering more thoroughly (deeper and longer) but less often is best? This method encourages deeper root growth. If you have our typical clay soils in your landscape, one benefit they provide is holding onto moisture longer, so make any supplemental irrigation you are providing count.
Practice sustainable gardening by watering only when needed. Simple tools like a rain gauge can help you determine if a summertime afternoon shower provided enough rain to meet your plants’ needs. (Image credit: Melinda Heigel)
Another important factor in sustainable irrigation is to water only when plants need it. You do this by simply paying careful attention to your landscape, containers, and plants. Look for signs like slightly drooping or wilting leaves; poke into the soil about ¾ of an inch with your fingers to see if the soil is dry. Consider installing an inexpensive rain gauge in your garden. On average, established plants need approximately 1 inch of water per week, which often can be met by rainfall and enhanced with additional irrigation as needed.
Although this seems like a no-brainer, water your plants at the right time of day. I can’t tell you how often I see sprinklers in yards and gardens running in hot mid-day summer sun — a less than optimal plan. Instead, watering in the early morning means better water absorption and less evaporation in the heat of the day. Day and evening watering might be necessary given your schedule, but you also might have unintended results due to wet leaves (see below).
Choose the Best Watering Techniques
Watering techniques can also be important to success. Whether you are watering with a hand-held watering can or hose, get the water down to the plant’s base where it touches the soil. Getting the plant leaves wet with overhead watering doesn’t get water to the roots where it is most needed, and prolonged wetness on the leaves can contribute to fungal diseases like powdery mildew or leaf spot especially during hot months. Overhead watering during the heat of the day can also be ineffective due to water evaporation. Using sprinkler irrigation on a windy day may mean you are watering your sidewalk instead of plants. For these reasons, sprinklers are not always the best solution.
While overhead watering alone doesn’t cause plant diseases like cerospora leaf spot and powdery mildew seen here, prolonged wet foliage combined with hot and humid weather provide perfect conditions for fungal pathogens to infect susceptible plants. (Image credit: Melinda Heigel)
Other irrigation methods like soaker hoses or permanent drip irrigation efficiently provide the moisture where plants need it the most. These methods deliver water slowly and deeply. Likewise precious water is less likely to runoff and water your concrete. You can use these direct watering methods virtually any time of the day without increasing disease pressure as foliage stays dry. Placing a soaker hose on a timer attached to your hose connection means you don’t have to remember when to water.
Innovative ways exist to provide supplemental irrigation that are low tech and effective. Collapsible bags filled with water around trees and shrubs slowly release water to ensure these newly-installed plants are receiving proper moisture. Just remember to keep them filled, of course. Even placing something as simple as a recycled milk jug, drilled through with small holes and filled with water in your garden bed can provide slow, steady moisture. An ancient technique by a pot called an olla (pronounced oy-ya) utilizes an unglazed clay vessel buried in the ground to deliver water. An unglazed, water-filled terracotta pot with a plugged drain hole buried in the ground next to plants and covered with a terracotta saucer suffices. Water slowly seeps out of the container to irrigate nearby plants. Again, you must remember to refill the pot and be careful not to damage existing roots when installing. Consider burying an olla as you initially install plants. These vessels take up room in the garden, so some people only use them near high-value plants. You can also try this system in containers.
Soil Coverage (Mulch is more than aesthetics)
Use Organic Mulch to Increase Drought Tolerance
Generally, uncovered soil around plants equals drier, poorer soils and potentially stressed plants. Using a couple of inches (typically 2-3 inches) of the traditional organic-based wood mulch (shredded bark, bark chips), pine needles, or compost is a great strategy to reduce plants’ water needs by keeping the root zone cooler. Mulch also keeps soil from crusting over, thus allowing better water penetration. Just make sure you keep the mulch off leaves and stems of the plants to prevent decay, disease pressure, and even rodent damage. This is true for tree trunks, too: no volcano mulching!
Incorporate Living Mulch
Using living plants in place of more traditional wood mulch leads to healthier plants, better soils, and less watering. (Left to right) A homeowner has replaced wood chips in their garden bed with bugleweed. A late fall view and a spring shot when the living mulch is blooming with purple flowers, which makes it an even better feature in the garden. (Image credit: Melinda Heigel)
Have you ever heard of green or living mulch? A new way of thinking about mulch is using living, growing plants to cover the ground in the place of “traditional” mulch. Farmers have incorporated cover crops like crimson clover and hairy vetch in their crop rotation schedules for a long time, and home gardeners are getting in on the action. By installing low-growing plants that act as ground covers in place of traditional mulch, these plants grow as an understory layer to your larger plants. The goal is to gain complete soil coverage once these plants reach maturity. Benefits to a living mulch include cost savings (they don’t have to be replaced annually like traditional mulch); healthier soils and plants (green mulch provides additional nutrients back into the soil, boosting soil health, and making plants in your garden grow deeper roots); and increased water holding capacity for the soil.
(Left to right) Note the creeping jenny (Lysimachia nummularia) ground cover used as an underplanting in a spring-blooming flower bed. If choosing creeping jenny, gardeners must keep a close watch on this ground cover, which can be overly enthusiastic around other plants in the garden.2 Here a gardener is establishing a living mulch of creeping moss phlox (Phlox sublata) in their planting bed. In early spring, profuse blooms brighten the landscape. (Image credit: Melinda Heigel)
When it comes to living mulches, look for spreading ground covers that are not overly aggressive or known invasive species.
Some Suggested Ground Covers for Living Mulch
For sunnier areas
-Prostrate blue violet (Viola walteri ‘Silver Gem’) Native, silvery heart-shaped foliage, with blue to lavender flowers, herbaceous perennial
-Plantain-leaved pussy toes (Antennaria plantaginifolia) Native, semi-evergreen, attracts pollinators
-Creeping thyme (Thymus serpyllum) Fragrant leaves, attractive pink to purple flowers, drought resistant
-Golden groundsel (Packera aurea) Native perennial, naturalizes rapidly, yellow flower
-Moss phlox (Phlox subulata) Spring blooming, attractive flowers, semi-evergreen
For shadier areas
-Bugleweed (Ajuga reptans) Dense creeper, semi-evergreen to evergreen, blue-to-lavender flowers
-Wild ginger (Asarum spp.) Prefers moist soil, so some shade is a must, semi-evergreen to evergreen foliage depending on species, heart-shaped leaves
-Sedge (Carex spp.) Native and non-native species, perennial, can be evergreen, grass-like, highly ornamental
-Bloody cranesbill (Geranium sanguineum) Clump-forming perennial plant, lobed leaves and small pink-to-violet flowers
-Foamflower (Tiarella cordifolia) Herbaceous perennial, lobed leaves, delicate pink-to-white flowering spikes
-Green and gold (Chrysogonum virginianum) Native plant, 1-2 inches in height, semi-evergreen, showy yellow flowers
-Creeping jenny (Lysimachia nummularia) Herbaceous perennial, semi-evergreen, can be overly vigorous grower, use where spread is not a concern
Watering plants in the summertime seems like such a simple concept, but it is often vexing to home gardeners. Doing it correctly and sustainably is vital to your plants’ success. Enjoy your summer in the garden and use these simple tips to make sure your plants do too!
Notes
A version of this article appeared in DCo Life, the Durham County Employee Magazine, summer 2024.
1—Of course, choosing water-wise plants for your garden or containers that are zone appropriate is also a great way to ensure summer success. Check out these online resources for more information and plant lists.
NC Botanical Garden’s “Gardening for a Drought: North Carolina Native Plants to the Rescue.”
Extension Master GardenerSM volunteers of Durham County blog post “Ten Plants that Can Take the Heat”
2–In some parts of the US, creeping jenny is considered invasive and some experts suggest its best use is in container plantings. Some advise to use as a ground cover only where invasive spread is not a problem. See NC State Extension’s Plant Tool Box link below for more.
https://plants.ces.ncsu.edu/plants/lysimachia-nummularia
Resources and Additional Information
Read about one Texas Master GardenerSM volunteer’s quest to install living mulch in her landscape.
https://www.startribune.com/a-master-gardener-makes-the-case-for-living-mulch/510676132
While this post doesn’t address proper lawn irrigation, it’s a hot topic during the summer. The EPA estimates that landscape water use counts for one third of all residential water use. Read here for best practices and sustainability tips for watering lawns.
NCSU’s Office of Sustainability’s link offers ideas for saving water in the garden this summer when irrigating.
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