In my region of Southern Ontario we are experiencing above average rainfall this year and the lawns and vegetation are lush and green. For many other provinces and states however they are experiencing above average temperatures with little rainfall. Keeping lawns and gardens thriving during these times can be challenging. Following are a few tips to help your lawns and gardens survive the summer heat and drought.

Lawns:
Drought-induced Dormancy: Soaring summer temperatures  and lack of rain fall can really take a toll on your lawn.  Many grasses will try to survive by entering a dormant stage where they drink less water and stop growing. According to Milorganite, lawns can survive without water for 3-4 weeks, at day time temperatures of up to 27 degrees C; but when those temperatures begin climbing past 33 degrees C that time frame is reduced to 2-3 weeks. If you are unable to provide the inch of irrigation that a lawn requires weekly to stay green you are best to allow it to enter this dormant stage and remain there until the end of the hot, dry season. To keep your dormant lawn alive you will need to irrigate it lightly, about ½ inch, every 3 weeks (more or less often, as mentioned above depending upon the average daily temperatures). This irrigation will not make a dormant lawn green again. Greening will start when conditions get cooler and wetter. 

To keep a lawn green over the summer you will need to provide a minimum of 1 inch of water per week. This will wet the soil to a depth of 4 to 6 inches (an average lawns root zone). To determine how much water your have applied set a water gauge or container in the area you are watering and once you have filled the container an inch you can turn the water off. If you make a note of how long it takes on average to put an inch of water on your lawn you should not need to measure each time.

Other lawn care tips to help you through the hot dry season:

• Infrequent and deeper watering prior to drought will develop deeper roots, which make plants much more sustainable.  
• Raise the blade on the lawn mower and keep the lawn tall throughout the summer. This will keep the surface of the soil from drying out, reducing the need for watering. Cool season grasses like Kentucky bluegrass, fescue, bentgrass, and perennial ryegrass should grow 2 ½ to 3 inches tall.
• Leave grass clippings on the lawn; clippings not only decompose and provide nutrients to your lawn but they also help to hold in moisture and shade the soil.
• Once your lawn has gone dormant fertilizing will not bring it out of dormancy. Apply your fertilizers spring and fall. This will give you nice strong roots that are better able to cope with the hot dry season.

TREES

This maple tree located on a center boulevard in Whitby, Ontario is exhibiting classic drought symptoms of leaf scorch. Leaf scorch appears as outer edges turning brown and curling (leaves may also brown between the veins). The damage is usually symmetrical beginning at the leaf tip and working back. The fact that the damaged occurs on the edges helps to differentiate it from a disease. On diseased leaves the damage occurs away from the edges and crosses the veins. Trees facing roadways and paved pathways are more prone to leaf scorch as the hard surfaces collect and reflect, concentrated heat. Plants on the south or west sides of buildings or fences also tend to exhibit more leaf scorch. 

Drought Damage:

• Conifers drop old needles followed by the tips of the needles turning brown. If the drought continues the new season’s growth may droop, gradually yellow, then brown; needles may also be shorter and twig size may be smaller. According to Ethel M. Dutky of the Plant Diagnostic laboratory at the University of Maryland, resinous bleeding cankers on large branches and main trunk may also develop. (Bleeding cankers are caused by a fungal disease. The cankers (the swollen areas) can expand and girdle the tree or branch).
• Evergreensgradually turn yellowish-green, then light brown. Discoloration starts at the top and progresses downward, and from the outside in. With prolonged drought conditions leaves may be smaller than normal, drop prematurely or remain attached to the tree even though brown. 
• Boxwood exhibits a general bronzing or an orange coloration of the foliage. They require at least 1″ of water per week.
• Drought damage may or may not reveal its-self right away. Often you see the effects of drought one to two years down the road when insects and disease move in to attack the weaken tree.
• Soil compaction will increase drought damage by not allowing rainfall and irrigation to penetrate down to the roots. Have the soil beneath the tree aerated (if compacted), then irrigate it regularly, keeping all foot traffic and heavy machinery off for the season.
• “99% of the root system of a tree is located in the top 3′ of the soil, and a good portion of these are in the top 12″.” (Dr. Sharon M. Douglas, of the department of Plant Pathology and Ecology at The Connecticut Agricultural Experiment Station). “This is especially true of feeder roots. When dry soil conditions occur, the feeder roots and root hairs shrivel and become non-functional.”

*Some Drought Tolerant Trees and Shrubs Include:
Trees: larch, bur oak, Colorado blue spruce, green ash, Douglas fir, amur maple,  mountain ash, red pine, eastern red cedar.
Shrubs: Crape myrtles, lilacs, smoke trees, junipers, boxwood, yews, caragana, potentilla, spirea, and hypericum. 

How To Water Your Trees:

• Water deeply and water slowly. You want the water to soak deep down to the roots not run off. Watering for short periods of time encourages shallow rooting which may lead to further drought damage.
• For deciduous trees water, with-in the ‘dripline’ (the outer edges of the tree’s branches) deeply, to a depth of 12inches below the soil surface. Coil a drip hose around the trees drip line or place your garden hose on slow to medium flow under the drip line. For smaller trees water bags and 5 gallon buckets  with holes punched in the bottom also work well.
• For evergreens, water 3’-5’ beyond the dripline on all sides of the tree.
• According to the CSU/Denver County Extension Master Gardeners your tree should receive approximately 10 gallons of water per inch of trunk diameter (measured at knee height) for each watering. Note: It takes approximately 5 minutes to produce 10 gallons of water when you hand water using a hose at medium pressure.

Note: It is not advisable to fertilize trees that are being stressed by drought. Encouraging your tree to put on new top growth will only increase the demands and stress on the tree also the fertilizer may potentially burn the roots due to insufficient water to dilute it.

ROSES:

Roses develop long tap roots that enable them to go in search of water and nutrients. Like other tap rooted plants they benefit most from deep, but infrequent watering. The American Rose Society advises that roses should receive 1 to 2 inches of water each week. Just how deeply the water penetrates will depend on upon the soil structure. In a sandy soil one inch of water will penetrate about 12″, in a medium loam about 7″, and in a clay soil about 5″. To help the water to get down to the long root zone try building a 4″soil basin around the drip line of your rose. Slowly fill the basin (careful not to break the sides of the basin down), let it drain then fill it again.

Other Tips For Helping Your Roses Survive The Summer Heat And Drought:

• In drought, do not cut blooms from the bush as they start to fade. Allowing flowers to form seed heads will help postpone the new growth that normally follows each blooming period. Do, however, remove seed heads soon after they have formed because they will use water to mature.
• Mulch (2 to 3 inches around a bush) to help retain moisture from watering and reduce future watering needs. Mulching also helps keep the soil cool and helps control weeds.
• Fertilizer should be applied sparingly. Feed roses just enough to keep them healthy without over-stimulating growth. A light hand with fertilizer protects against fertilizer burn as well.
• Plants under stress are more likely to attract plant pests and insects and to develop disease. Help to keep your roses stress free by nourishing them an inch or 2 of water per week.

Perennials:
There are no hard fast rules (that I know of) for how much to water perennials. Each plants requirements can be quite different. Some like it dry while others like to remain constantly moist. As a general guide: 

• New and less established plants will require more frequent watering. This is due to the smaller root ball and its inability to reach the moisture located deeper in the soil.
• Tap rooted plants tend to require less frequent watering (but this watering, as mentioned must be a deep watering).
• Native plants tend to survive heat and drought well (with little supplemental water) if heat and drought is common to your area.
• Larger plants usually require a larger amount of water at each feeding.
• Shade lovers tend to prefer moister soil and will require more frequent watering when grown in sunnier areas of the garden.
• Mulch your perennial beds and add plently of organic matter to your soil. Both serve to hold moisture in, reducing future watering needs.

Heat Exhaustion:

Some plants like this Ligularia do not much like the heat. No matter how much you water them they tend to go limp during the heat of the day. They will usually perk up again when the cooler evening temperatures arrive. However this year’s heat wave with it’s hot evening temperatures have not been offering the plants much relief. Another plant that tends to droop in the heat are hydrangeas. About all the home gardener can do is to ensure they remain well watered and wait for the cooler temperatures to return. (Note: Caution not to over water. Some gardeners mistake the drooping for lack of water. Check the soil first, and only water if the soil is dry to the touch). 

Leaf Scorch

Leaf scorch commonly occurs on lower light loving plants like this black bugbane, hostas, astilbe, solomons seal, tuberous begonias…and more. Typically permanently relocating them to a shadier, moister location is your best solution. However during extended periods of drought and heat almost any plant can become scorched including large shade trees. During these periods keep your plants, including your trees well watered. 

*Drought Tolerant Perennials:

Artemisias – (Artemisia species)Blanket flower – (Gaillardia x grandiflora)Blue fescue – (Festuca cinerea)Creeping phlox – (Phlox subulata)Creeping potentilla – (Potentilla neumanniana)German statice – (Goniolimon tataricum)Globe thistle – (Echinops ritro)Hens and chicks – (Sempervivum tectorum)Ice plant – (Delosperma species)Lambs ear – (Stachys byzantina)Lavender cotton – (Santolina chamaecyparissus)Little bluestem – (Schizachyrium scoparium)Oriental poppy – (Papaver orientale)Ozark primrose – (Oenothera missouriensis)Penstemon (Penstemon species)Plumbago – (Ceratostigma plumbaginoides)Poppy mallow – (Callirhoe involucrata)Prairie coneflower – (Ratibida columnifera)Prairie dropseed – (Sporobolus heterolepsis)Purple coneflower – (Echinacea purpurea)Russian sage – (Perovskia atriplicifolia)Snow-in-summer – (Cerastium tomentosum)Stonecrop – (Sedum species)Yarrow – (Achillea species)

*A few drought tolerant annuals to choose from include:

• Cosmos – (Cosmos sulphureus)
• Creeping zinnia – (Sanvitalia procumbens)
• Blanket flower – (Gaillardia)
• Sun flower – (Helianthus annuus)
• Dusty miller – (Senecio cineraria)
• Annual mallow – (Lavatera trimestris)
• Spider flower – (Cleome hassleriana)
• Morning glory – (Ipomoea spp.)
• Narrow-leaf zinnia – (Zinnia angustifolia)
• Zonal Geranium – (Pelargonium zonale)
• Annual fountain grass – (Pennisetum setaceum)
• Globe amaranth- (Gomphrena globosa)
• Gazania – (Gazania rigens)
• Lantana – (Lantana spp.)
• Verbena – (Verbena spp.)

Photo credits: all photos taken by the author.

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