Tips for Keeping Gardens Cool in Summer

Design and InstallationGarden Caregarden TriviaIndoor plantsPlant Health Care

Aug 13

Written By Peter Morris

People sweat to cool off, and plants do something similar. We call it transpiration.

Water evaporation from leaf is called transpiration

Cooling effects of transpiration

As summer heats up, some of the water drawn up through the roots exits the plant through pores – or stomata— which are in its leaves. As it evaporates, heat is removed, providing a cooling effect.

However, if there isn’t enough water available or if the relative humidity gets too high, the stomata close. If this happens, the plant heats up, ceases to grow, and can eventually die.

Water movement from transpiration

Evaporation of through the leaves doesn't just cool the plant, it runs the whole system. The vacuum created as vapor escapes pulls water up through the plant tissues, and the water pressure in the cells keeps the green parts of plants firm and upright.

Because water is also necessary for photosynthesis, in high temperatures there is competition for this resource. As more is used for cooling, there is less available for making sugar.

Heat wave ! - Above 95*F

At 95*F most plant cells begin to suffer cellular damage. Except of course plants like cacti and desert plants which evolved in that heat ! If the air temperature stays over that point for a long period -- especially if it doesn't drop at night – the plants won't get a break and suffer lasting harm.

Above 95*F most plants are in cooling mode with little photosynthesis. Some actually shut down altogether a process called aestivation or summer dormancy.

Constant wilting ? - change your plant containers

Some containers dry out quickly, and may need to be watered every day in the summer heat. Perhaps even more often if they are small or in a sunny location. And porous containers like clay will dry out the fastest.

It may be possible to move small ones into the shade on the hottest sunny days, but for most larger ones this is impractical. Instead, try using non porous plastic, resin or metal planters.

Wilted pansies from lack of water

Mulching

In hot weather, sunnier parts of your garden will dry out faster. Place the heat tolerant ones there. However, laying mulch over the plants' roots insulates the soil and greatly reduces evaporation. They will do better.

Mulch those pots !

Plant selection

Some very cool loving temperate-zone plants are easily scorched or wilted. Japanese maples for example evolved in cool moist forests – so they are less likely to tolerate a hot sunny rooftop. Annuals like pansies, cineraria, and osteospermum simply can't handle the heat.

Try using plants that better tolerates a strong sun and summer heat. Many native to tropical rain forests simply shrug off stifling heat and humidity. Hibiscus, lantana, geraniums, and many other annuals are high heat tolerant.

Lantana LOVE heat – and so many varieties !

Location

Location, matters also. Plants next to a concrete wall will receive reflected heat. A/C units exhaust and radiate heat and blow hot air with temperatures much higher than the thermometer says.

Transplanting

Young plants or recently transplanted ones, with scanty root systems, have fewer defenses and suffer a lot. Plant during cooler weather.

Heat stress damage - plasmolysis

Plants that wilt will usually recover again quickly after they are watered or cooled off. However, too many of these wilt and rehydrate cycles are not good.

Persistent or repetitive wilting leads to leaf cells becoming plasmolized. They get permanently damaged and stop functioning properly.

Color and shape changes

Leaves lose their green color and become yellowish, pale, or grayish. They may even get scorch marks on the blade. Some plants' leaves (grasses) may curl. Bamboo for example will roll up like a cigar if wilting or exposed to high temperatures.

Summer dormancy - Aestivation

Some plants evolved to actually shut down altogether when it gets hot. This is a process called aestivation or summer dormancy. Most cool loving plants stop blooming altogether – try getting a flower out of a Osteospermum in July !!!

Cool weather loving Osteospermum

So what is your best garden strategy for dealing with the heat ?

Call Plant Specialists Today !

We have the people, experience and knowledge of which plants to choose to take our extremes of cold, heat and humidity.

So even in hot spells, you can worry less.

GREENING NEW YORK FOR OVER 52 YEARS !

Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBA

All photographs used with permission from @SHUTTERSTOCK

Peter Morris

Peter was born and raised on a beautiful green island in the midst of a tropical rainforest. He was introduced into the world of plants at the age of six when his grandmother, an avid Spanish gardener herself, asked him to help her grow seeds for her pepper garden. He was hooked! By the time he was a teen, he had his own rose and orchid collection numbering in the hundreds. Botany was in his blood, and that is what he set out to study.

His passion brought him to NY in the late seventies to further his education. His tenacity allowed him to work full time at Plant Specialists while he completed a MS in Plant Biology. As a manager at the time he felt unsatisfied with his knowledge of business and business processes. Peter felt compelled to learn, so he then pursued and completed an MBA in Quality Management within a few short years.

Peter’s other passion is teaching. His natural ability is quickly consumed by our staff in all subjects in Botany, Horticulture, and Landscaping. He created an immense reference library of more than 3,500 plants providing an invaluable resource for our staff.

Peter’s breadth of knowledge and wisdom allows him to effectively diagnose the needs of plants. Sometimes just by walking into a garden he can create a prescription that fixes even the hardest issue. He is our Staff Botanist, Diagnostician, and all around Mentor. Recently, he has put his immense knowledge and skills into developing a new department that focuses on Plant Healthcare. As he puts it, “Magic through Science”. The PHC staff that surround him have avidly consumed his teachings. Substantially developing their own plant wisdom, many have taken on difficult plant health issues with spectacular results.

Plant Healthcare has been an instant success with customers! The proper treatment of insects and diseases including Organic methods has made pest control a necessity for every plant. Correcting hormonal imbalances caused by planting in containers or refurbishing soils leached of nutrients by irrigation systems are big challenges PHC has become quite comfortable addressing. The scientific approach to the complex demands of keeping plants healthy in our harsh city environment has made many a customer say WOW!