Do you have a deck that is so hot in the summer everything you plant out there dies of heat stroke? Nothing is more disappointing than watching your plants shrivel up and die during a summer heat wave. You can avoid the pain and disappointment of dead plants by buying the right containers, using the correct soil mix, and choosing the best plants for wind and heat.
Containers for Hot Conditions
Look for large, deep, thick walled pots. The least expensive containers are plastic. Polyethylene pots usually have thicker walls and are more crack resistant than plastic. They are also probably twice the expense. Glazed clay pots (often made in Vietnam) are sometimes the most attractive sort of pot, but like Terracotta tend to wick out moisture from the soil. Terracotta is not a great choice for a really hot dry deck although they may be the only choice for plants whose roots need a lot of oxygen to thrive, such as orchids, and many herbs. Both terracotta and glazed clay pots need to be protected during cold winters. You can empty them out completely and take inside, or you can leave them in place, wrap them in plastic to keep out snow and rain. It is the contraction and expansion (freezing and thawing) of water inside the pot during the winter that can cause it to crack.
A general rule is to choose deep pots rather than shallow pots. The deep pots will keep the plant roots cooler thus aiding immensely in their survival. Exceptions to this rule are Succulents and Cactus that usually prefer a wide shallow container instead of a deep cool pot because they like the soil warm, dry, and well drained. Just to make it complicated, there are many plants such as Lavender, Rosemary, and Orchids that like their roots cool and moist but need the surface of the soil to be dry. Using a mulch that dries quickly, such as buckwheat hulls or sand will help achieve these special conditions.
Containers with reservoirs in the bottom are helpful for keeping soil and plant roots moist. These pots are sometimes called “self-watering”. Don’t be fooled, you still have to water, only not as often! Seriously, a reservoir in the bottom of a container can be helpful, but watch out you don’t over water your plants by never letting them dry out at all. That can drown the plant and make the soil anaerobic (without oxygen). Plant roots need water and oxygen to keep the plant healthy.
Moisture Retaining Potting Soil
When you are preparing soil for your containers, make sure to add water absorbing polymer crystals. Follow the directions carefully because if you add too many crystals your soil will end up heaving out of the containers and making a real mess. Blend one 1 part vermiculite based potting soil to 2 parts sweet compost, such as Coast of Maine. Avoid using composted manure in your container garden unless it is well composted and smelling good. Mulch the top of your containers with shredded bark mulch, buckwheat hulls, or sand.
Heat Tolerant Plants
Shrubs and Trees can be great assets to your deck container garden, but they need very big pots to survive. Make sure that your deck or porch can hold the weight of very large pots before you begin. They will get quite heavy when wet with water.
A way to guide your plant selections is to determine if your heat is moist or dry, and then look to the natural places that are either hot and humid, or hot and dry for ideas. Desert plants live in the desert because they are adapted to the climate and like it hot and dry. Seashore plants live where it is hot, and maybe cold, and humid. Tropical climates are also hot and humid.
Best choices for searing hot weather include plants with small leaves, especially needled evergreens. The needles are just tiny leaves. Small leaf size reduces the amount of moisture that can evaporate from the plant. Plants with large leaves can transpire much more water thus removing moisture from the entire plant. Large leaves will wilt and dry up quickly when they get too dry.
Obviously, these plants like us need water to live, so you need to set up a watering system. You can buy special irrigation systems, that are not that expensive, for containers that attach to either a timer on an outdoor water faucet, if you have one of those on or near your deck, or to a large bucket of water from which the containers wick water. Someone has to fill this bucket regularly though. I use a regular size garden hose that I attach to the water faucet at my kitchen sink to water the containers on my hot, dry, windy porch.
If you take the time to make the right choices for your deck garden, you will enjoy it immensely and not have to worry about plants shriveling up and dying in the middle of a heat wave. Be prepared!