We have had quite a streak of 90 plus degree days in the past 3 weeks. It has been enough to make even the most passionate gardener wilt. Even the corgis want no part of it. Getting in my fountain at the end of the day has been a regular thing lately. Intense heat can play special havoc with gardens in containers, as technically speaking, their roots are above ground. They also are completely dependent upon you for water. But there are some things you can do to help your containers cope with the heat.
The obvious solution is to pick plants that like to be dry. Succulents, echeverias, agaves and other desert type plants can survive long periods without water. I am told that agaves have lived on the roof of the Vatican for 300 years-I am quite sure no one waters them. Plants native to desert like environments have adapted to do well with little water. Being from the Midwest, I am not such a fan of these plants. I would starve, only having succulents to look at in my pots, so I look for other solutions. Diamond Frost euphorbia and variegated licorice will not suffer the gardener that waters them too often. Once established, I only water when they are really dry.
You can buy a little time if you grow annuals in window boxes. The big idea here-a giant soil mass dries out slowly, rather than twice a day. When soil heats up, the rate of evaporation of water from that soil gets to be speedy indeed. I have seen clients splash water on their pots from a watering can-this is not watering. I fill this window box to the top with water, let the water soak in, and fill the box again. I repeat this until I see water raining out the bottom. Water your pots thoroughly, not lightly. This box sometimes goes three days before I need to water again.
Automatic irrigation for annual plants can save you hours of time, but you have to be sensible with it. Water automatically when there is a need, not automatically. Patty at Bogie Lake has been watering annual crops for so long she can tell if something needs water by looking at the leaves. She says the green color will change when a plant is dry. Barring this type of watering skill, put your finger in the soil to see if it is dry. So many people plant impatiens in ground, as it is so tolerant of water from an irrigation system. The cosmos in this bed I let go to the dry side before I water. Most annual plants love the heat. 90 degrees they handle with aplomb; it is 90 degrees without water that is a problem.
Small containers in full sun locations are not for everyone. Not everyone can water twice a day if the temperatures are over 90. If the time you have available to water is short, use fewer, and bigger containers. If you must have smaller containers, choose plants that don’t mind drying out, or plants of easy culture. The only thing that ever seems to bother petunias much is too much water. These mini cascade geraniums are amazingly tolerant of hot and dry conditions. They also bloom long into the fall. I wonder why I do not see them used more often.
A grape vine and some angelina is a dry and hot tolerant combination, and much more verdant looking than hens and chicks. Plants liking a long root run, as do tomatoes and grapes, benefit from deep soil more than wide soil.
Topiaries grown from shrubby material such as these eugenias are not fussy either. They never seen to be bothered by heat, and they tolerate imperfect watering. Choosing plants that are native to hot and dry environments are perfect for your full sun terrace.
When plants grow together, they shade the soil. This slows the rate of evaporation from the soil much like mulch does. I may groom old leaves out in order to keep good air circulation, but I let the plants provide a shade barrier to the soil. A hanging basket that has gone bald on top and is showing soil will dry out very fast. Most plants do not like to be watered every day, but when the temperature soars, you may need to do just that, to keep them alive.
Be thoughtful about where you place your containers. A little shade from trees or shrubs can help your post stay good looking. This pot has enough exposure to the sun to stay good looking, but not so much exposure that they fry. Group pots together; one large pot planted with a topiary lantana can handle any amount of heat and sun. Other pots grouped with it will benefit from the umbrella. Other plants that make great umbrellas are datura, irisine, nicotiana mutabilis (pictured above) and grasses.