During extreme heat your best ally is the same thing that is your best friend during extreme cold;  Mulch!  The Summer heat here in Oklahoma is extreme and though the exposed part of the bushes would be your first guess as to which part to protect that would be wrong.  The roots of the rose are the most susceptible to heat.  This is especially true for container grown plants. 

When you have a good layer (I like no less than 4 inches) of mulch on the ground it insulates the ground from the sun as well as it does the cold.  In fact when you wet the mulch when watering the roses the root zone temperature is actually lowered through evaporative cooling.  Mulch should stay around your roses 12 months of the year.  It is not necessary to pull it back from the main stem at anytime of the year as some will advise.  Mulch right up next to the stem will assure the rose is protected and will do no harm.

As I stated earlier roses in pots are especially in danger during the summer heat.  If you have been to Roses inc. through the Summer you will see Coolies on the pots.  These coolies keep the roots of the roses from overheating and keep the bushes pretty and green.  I invented the Coolie several years ago and when used it makes all of the difference in the world in the roses appearance and vigor during the hot Summer months.   If you have roses in pots you must take steps to keep the roots from overheating.  Mulch is generally not a practical solution for keeping the sides of the pot and hence the earth inside cool.  Your best option is to shade the pot from the afternoon sun.  This can be done with anything that can be draped around the pot that provides good insulation.  You can provide even more protection for the rose by doing your watering mid day so the water will cool the soil.  It is not true that water on the leaves in the bright hot sun will burn the leaves.  In fact, just the opposite is true.  A cool watering during the hottest part of the day will go a long way toward relieving heat stress.  I have found that wetting the foliage during the early afternoon really perks the bushes up.  This is true whether the roses are in the ground or in pots. 

One word of caution, Be sure that you do not use the first water from the hose on your roses.  It can reach temperatures of well over 100 degrees in a black hose setting out in the yard in the direct sun.  Run the water until it is cool to the touch before proceeding with your watering.

 

Transpiration, a big word for a plant sweating.  Yes plants do sweat as part of the photosynthesis process.  Because of this plants use more water at some times than others in direct relations to atmospheric conditions.  Does this mean they need more water to survive in the hot summer months than when the weather moderates?  The short answer is yes.  Is it possible to overwater roses in the summer?  Again the short answer is yes, especially if the roses are potted.  The important fact to remember is that the roses roots must also breath and they can no more do that than we can under water. 

Many of you have heard me say that 1 inch of water a week or about 5 gallons poured at the base of each plant is sufficient even in the warmest time of the year.  This is only true if your roses get 1 inch once a week throughout the year.  If you water your roses a little, multiple times a week, the roots do not reach out for available nutrients and moisture that are present deeper in the soil.  When that is the case you must continue to water more often.  Here at Roses inc. I will probably water the rose gardens once this month, that is unless we get an inch of rain.  No, the roses won't die because they have grown deep roots during the spring and early Summer as the moisture evaporated and or transpired through the plants more quickly the roots were forced to reach out deeper into the soil so now they have a root system capable of taking care of the plants water needs even in these severe conditions with little supplemental watering.  Remember the key is that you must begin this process early in the year.  Roses that have been watered a little multiple times a week will die if that is not continued.

When to Water

 Watering should be done only after the top 1/2 inch of the soil dries to the point it will not stick together.  Leaves turning clean bright yellow and falling off is a sign that you are watering too much.  Under watering will be indicated by the plant wilting or the leaves drying without turning yellow or falling off.

 

 The time of day you water is also important.  The roses should be watered after 7 a.m. but before 6 p.m. this time of year.  Especially when watering over the top of the plants this is important to help prevent disease.  Remember that it is not at all harmful to the roses to spray the tops during the heat of the day and in fact they will appreciate the cool down.

Yes as long as the weather is hot and dry the spider mite will be a problem.  The most effective control is Tetra San which we stock here at Roses inc.  Malathion will also be effective but it must be sprayed on the roses every 3 days for 9 consecutive days for control.  Lastly a very hard spray of water directed at the underside of the leaves will help keep populations a bay.  Any pest is better prevented than controlled so check your plants often.