Pass The Sun Block Don't Let Summer Give Your Container Plants The Hotfoot. Every spring, thousands of plants get lovingly placed into pots, planters, tubs and every conceivable container imaginable. We carefully tuck them in with the best potting mix we can get our hands on, water them and feed them with the best food we can find. Then we proudly place them in places of prominence to let them show off their beauty and delight us. For weeks they grow and bloom wildly, showing us new growth and blooms daily. Then summer comes with its scorching heat and drying winds. The plants that once delighted us start to sulk and wither. Their leaves droop and the flowers that once delighted our eye start to be scattered around the ground like so much spent confetti. We water till we can't afford it any longer, but sadly, we resign ourselves keeping watering ever more and hope they might once again spring forth when the weather cools. For some plants, we prematurely give up hope and toss them into the compost remembering the few weeks we had to enjoy them. Sound familiar? Sadly, this is all to often the case with our container plants. But the heat of summer does not need to be the end of the joy that container plants can bring. Often the answer can be a simple fix, but just as often, the answer lies at the beginning when we first choose a container and place plant into pot. When we make a choice to beautify our patio or deck with potted plants, we need to consider that for most of us, summers heat will come whether we like it or not. We need also to remember that potted plants are confined to a relatively small growing area with little ability to forage for additional moisture. Along with this, the growing area is normally placed out in the open where it is exposed to all of the harsh brutality of the summer sun. So what do we do? Give up on container plants if we have hot summers? Enjoy them while we can and then consign them to the compost? It is a fact that many folks do just that, but this practice is not one which needs to occur for most gardeners. Here's a few tips to help prevent your container plants from getting the "hot-foot". Choose plants that are drought and heat tolerant.
Just about anything that grows is a candidate for a container of some sort. This includes trees of many species. A good example is the "Orangeries" that were so popular from the 17th to 19th centuries where citrus trees of all types were grown in large containers for decades. Other examples are the Chinese and Japanese who grew many forms of large trees and shrubs in containers that could be moved around as the or mood of the garden changed (most often referred to as "Chi", or life energy in Oriental cultures). In Europe, containerized trees were popular during the 18th and 19th century. You get the idea.
In shopping for container plants, you will need to determine whether to plant annuals or perennial plants or perhaps a combination of both. Each of these will be treated a little differently. Annuals will often be a little less particular in your choices of containers because they are "hardwired" to perform at a particular level during their short life-cycle, set seed and die in a single growing season provided they are given minimal conditions. As a general rule, annuals will provide you with the most color, but will require the most water and fertilizer in order to keep them performing at their best.
Perennials however, will provide you with visual interest and often height and dimensional qualities that cannot be matched with most annuals. Many of these can provide you with seasonal flowers and perhaps fall color as well. The use of perennials in your container garden can serve as an anchor or backdrop for your annual displays. However, in most areas you will need to provide for winter protection for your perennial plants.
When shopping for plants, look for those that are drought and heat tolerant. Here, it is strongly suggested that you shop at a reputable nursery in your area where they have knowledgeable people to assist you in choosing plants that will do well where you live. Plants that will do well here in the Ozarks of Missouri, may not be appropriate in your growing area. Avoid shopping at those big box stores and relying on those little tags that are on the pots. These will only tell you general characteristics about the plant and not how well they will perform in your area or application. Additionally, the employees of these stores tend to have little or no training with the plants offered, so seek out your local professional nursery professional or county agricultural extension office. Many on-line nurseries provide excellent sources of information because they are continually collecting data from growers all over their respective countries they service. If in doubt, ask.
Choose the right container.
Containers come in all sizes and shapes which are often designed more for the pleasure of the purchaser than the benefit of plants. Yes, the appearance of the container can be very important, especially if it is to grace your patio and add visual interest. However, you must consider the fact that it is your plants that must live with your decision more than you. A small, dark-colored container or basket that looks really great to you may leave your plants languishing (or worse) in the hot sun of summer.
In choosing a container, choose one that will provide as much soil and root-room as possible. As a general rule, choose one that is no less than two-thirds the size of the full grown plant or plants unless you plan on up-potting later, watering continuously or growing the plant for only a short while. But, up-potting during the heat of summer causes a lot of additional stress on your plants at a time when they are already stressed by the heat of summer and continuous watering can place stress on your pocketbook. For annuals, this may not be quite as important as for perennials, but the container should still be large enough to hold enough water to sustain the plants without having to water more than once per day.
For perennial plants that will continue to grow larger for many years, in most cases you will need to try to size your container large enough so that it is roughly two-thirds the size of the plant at the end of the first or second growing season. An exception would be for such perennials like trees and shrubs that you plan on growing to a particular size and then maintain them at that size, much like in Bonsai. In this case, you will need to up-pot your plants almost yearly until you have reached the size of container and plant you ultimately wish to be at. At that point, you will need to unpot the plant every year or two, prune the roots and top to the desired size and replant.
In any case, the point is to provide a container that is large enough to provide enough moisture to carry the plant throughout the day. If your container requires watering more than once per day in the heat of summer, your container is probably to small. Consider removing some plants if you have multiple plants in the container or up-potting.
When choosing your container, also consider the material the container is made of. Traditionally, unglazed earthen pots were the only containers available and these are still desirable for such plants as cacti and other plants that prefer a dry environment because they help prevent waterlogged soil. They are also often preferred by some purists who choose to grow in much the same manner as gardeners of old. However, unglazed containers have the distinct disadvantage of wicking moisture away from the soil. I just said in the previous sentence that this was a disadvantage. Actually, this may not be entirely true if the unglazed container is large enough. During the heat of summer, the wicked moisture evaporates and actually cools the container, much like an evaporative cooler cools the air around you. However, while this phenomena can be a great way to keep your pots cool, the container must be sized accordingly.
Glazed earthen containers prevent this wicking action and are relatively slow to heat up when compared to most plastic or metal containers. However, any non-breathable container has the potential to cause the soil in them to become waterlogged unless you compensate with a well-drained soil inside. Unglazed, earthen containers do have one distinct drawback though. Because they absorb moisture that will freeze during cold weather, they are susceptible to freezing and breaking when they freeze. So if this is your container choice, you will need to provide winter protection for your containers by either storing them where they will not freeze or by removing the plant in winter and storing the container where it will not freeze. The unpotted plant can be placed temporarily into another container or "balled and burlapped" for winter storage.
Most gardeners who are choosing planting containers will be making a choice between glazed earthen containers or plastic. Either one has its advantages and disadvantages as long as they have proper drainage. Glazed earthen containers have the advantages of being heavier and more stable in high winds and because they are earthen, tend to heat up slower than most plastic containers. Another advantage is that because they are glazed and don't absorb moisture, they are less likely freeze and break in winter. Glazed earthen containers can also be a big advantage in early spring and late fall where they absorb heat during the day and release it relatively slowly at night, thus keeping the soil warmer. However, this physical trait of holding heat can be a disadvantage in summer, as your goal is to get rid of heat, not hold it.
Plastic containers have become increasingly popular because they are relatively inexpensive, attractive and readily available everywhere. You can find plastic containers of every size, shape, color and design just about anywhere you go, even your local grocery store often has them available. Like glazed earthen containers, these do not absorb moisture, and they are relatively stable in winter. However, they do have some disadvantages. 1) They tend to heat up relatively quickly. This allows the soil inside to heat up quicker than other types of containers. 2) They are generally quite light. While being an advantage if you need to move them, this lack of weight can be a disadvantage outdoors in high winds unless steps are taken to compensate for this.
Plastic containers will generally be one of the first containers to need supplemental protection from summers heat. One relatively new development in larger plastic containers is a double-wall construction, which leaves an air space between the inner and outer walls. While I doubt this advantage is designed into containers for the gardeners advantage, it is an advantage. This physical trait is probably there for the advantage of the manufacturer. This is generally the result of manufacturing the container using a technique called "blow-molding", where a small amount of hot plastic is "blown" around an inner and outer mold to create the shape of the container. The double wall construction also provides the ability to add strength and rigidity to the container without adding more plastic. In any case, this advantage for the manufacturer also serves as an advantage to the summer container gardener by providing natural air insulation for your plants so seek these out when shopping for large plastic plant containers.
One disadvantage of many plastic containers is that they have a relatively low resistance to ultra-violet radiation from the sun. This will cause the containers to deteriorate and become brittle over time. Generally, the cheaper the pot, the faster this will occur. When this happens, the container will need to be replaced. There are chemicals (usually silicone based) that can be applied to plastics to prolong this degradation, but it will need to be applied and reapplied regularly, thus increasing your maintenance duties.
One other potential drawback for plastic containers is that external finishes are often painted or applied to the outside of the containers. These often make the container more attractive and thus more appealing to potential buyers, but as a general rule, these are usually painted or applied as cheaply as possible, using the cheapest materials possible and seldom last long. When this happens, crafty gardeners can repaint the containers, other gardeners may have to live with a less attractive container or replace it. Applications of clear acrylic coatings can prolong this finish, but eventually the finish will deteriorate, leaving the surface unattractive. I prefer to paint the exterior of these containers with an application of either a solid color of paint designed for plastics or a textured paint for plastics for added interest. These generally last a couple of two or three years and then need to be reapplied. However, by repainting, I can change the color scheme of my container garden from time to time.
One other container material that is becoming increasingly popular is metal containers. They are now available in a variety of shapes, sizes and materials. Actually, metal containers of one type or another have been around for as long as man has been commercially working metal. When your mother or grandmothers wash tub finally wore out or rusted through, it would often find a second life as a container for flowers. However, from the standpoint of heat resistance, metal containers heat up the fastest of all containers. The soil inside of metal containers can quickly heat up to the point of killing the roots of your beloved plantings. These containers are ill suited to be placed where the summers sun will beat down on them, especially the hot sun of mid-day.
Additionally, metal containers that will deteriorate over time, such as steel or even galvanized steel, will need regular, periodic maintenance in order to keep them attractive and serviceable. The exception to this being copper, bronze or brass, which oxidize to a blue-green patina color, which is sought after by many. Regardless of metal type, metal containers are among the worst containers to choose from the standpoint of your plants health in summer.
Choose your color wisely.
Going back to your basic high-school science, dark colors absorb heat faster than light colors. Therefore, dark colored plant containers will get hotter, faster than light colored ones. This can be a critical factor in plant survival. I know that occasionally, dark colored containers may fit in better with certain decorating schemes, but we are talking about the benefit of your plants here, not decorating themes. It would be better for your containerized plants for you to change your decorating scheme than to have your plants languishing in containers that act as slow ovens on their roots. However, if it is necessary to use dark colored containers there are some options. 1) choose plants that will tolerate hot soil such as daisies, butterfly weed, yarrow and many of the grasses, etc. 2) Repaint the containers you have so they are lighter colored.
Repainting with an appropriate paint can be much less expensive than purchasing new ones. The principal is simply this, a light color reflects more sunlight away from it than a dark color and therefore absorbs less of the suns energy. Thus cooler soil and happier plants. This not to say that light colored containers will not absorb any heat, it simply means that light colors will absorb less heat.
While a flat white reflects the most light, it can be boring if you have many containers. Try using different shades of white, tan, light colored pastels, etc. and don't forget about the textured paints. These can add a great deal of visual interest to your containers. Additionally, the judicious use of paint opens up a whole new world of container choices that can be used. Painted wooden boxes with a little additional protection from some polyurethane on the inside, now become attractive planters that have a great deal of insulative properties from the wood.
Location, location, location
The location of your potted plants can have a huge impact on the success of many of your plants. Many plants placed in the middle of a patio that sits in full sun all day are much more susceptible to heat stress than ones that are placed where they receive some afternoon shade. If a tree is not available, seek the afternoon shade of a building or create some form of screening that will cast shade over your plants at midday.
Even placing your plants on areas covered by an expanse of wood, like a slatted platform or some form of fabric like a large area rug will keep the area from absorbing as much heat as the surrounding area and provide an insulating barrier between a hot brick, stone or concrete surface.
Mulch your containers.
One area that often goes unnoticed is the soil surface of our containers. We know the moisture holding and cooling value of mulch in our gardens and we mulch our garden plants faithfully. However, when it comes to our container plants, we tend to forget that these are but tiny slices of a garden loving crafted into a complete garden. Why would we not want to incorporate mulch here as well?
As any gardener knows, a mulch covering can be almost anything that will cover and shade the ground. However, for our container plants we need to apply some basic guidelines that are a little different than our general garden or landscape. In this case it must posses cooling properties. This generally limits us to an organic mulches because they tend to hold moisture within their structure and provides more evaporative cooling than non-organic mulches. Also, most non-organic mulches tend to absorb heat, which is something we are seeking to avoid. They must look attractive because our container plants are generally in an area of high visual traffic. However, the attractiveness of any mulch is in the eye of the beholder. Therefore, you may find yourself taking a bit more time in considering your choices. I find that coconut coir and peat moss make very attractive mulches. But you can also consider such materials as Sphagnum moss and dried Irish moss (this is normally a dried Spanish moss harvested from trees in the swamps and sold at craft and flower shops) to be very attractive and functional. I personally have an affinity for the dried Irish moss where appearance is important
I personally do not find dried grass clippings to be unattractive, but as as said before, beauty is in the eye of the beholder. Cocoa fiber mats that can be cut to fit your containers are yet another option, but tend to be more expensive than other forms of mulch. Ground straw is an excellent mulch, but straw needs to be "dulled" before use by allowing it sit out and weather for a few weeks prior to use otherwise, the reflective ability of bright straw can burn plant leaves from the reflected sunlight.
Stones and other non-organic mulches can be quite attractive as a mulch, but I would never use these unless I first applied an insulating disc of Styrofoam between the soil and stones first. This will prevent the non-organic material from transferring heat to the soil. If you use Styrofoam discs and non-organic mulch, cut the discs to size and shape, then cut the discs in half for inserting into the containers. This will make insertion easier and allow water to pass through faster.
Cool your containers.
One of the oldest and most efficient forms of cooling is evaporative cooling. This is the simple process of evaporating water vapor absorbing the surrounding heat and dissipating it away. This simple process can be experienced just by being around a large body of water such as a lake or large river. The water evaporating from the water will cause the surrounding area to much cooler than other areas further from the water, especially on the down-wind side of the water. When it comes to cooling potted plants, this can be as simple as wetting down the containers and surrounding hard surfaces.
Simple automated systems are available to create a constant, water-cooled area or your can create a simple wetting system with just a few sprinkler nozzles and a programmable timer set to turn on several pre-set times per day. Incidentally, mist and wetting systems will have the added advantage of making the patio area much more comfortable for you as well.
Insulate your containers.
Insulating your containers to avoid soil heating can be a simple process, but it may require a little planning, possibly some practice and probably the purchase of a few materials. Let's start with what I consider the easiest to the more difficult: Place simple curtains around your containers for shading and a whole new look. These can be as simple as an old bed sheet (purchased at yard sales for practically nothing) that is cut down and sown into a curtain and hung around the container. A decorative curtain can be constructed by forming a ring out of flexible copper tubing that is approximately 3 inches larger diameter than the pot and held around the top of the container by simple hook brackets that are made from heavy wire (similar to curtain rod hooks). The container end of the hook is pressed into the soil and a hook on the other end holds up the curtain rod ring (looks like an "ell" with a hook on one end). The curtain is threaded onto the copper rod like a regular curtain rod and hung on the hooks.
Another simple method is to simply create an open sided bag and install a drawstring in the top and ties along the edges to hold it closed. The bag is placed around the container and tied shut along the edges. The top is then drawn partially closed at the top and tied.
Place your container inside of a larger container that is approximately two to three inches in diameter larger than the original (centered). Now insert foam packing peanuts between the two containers. Pack the foam lightly and evenly around the containers so you don't push the inner container off to one side. Cover these with a few decorative stones if you like in order to hide the insulation.
Insulate the outside of your container with one inch rigid foam insulation (the type used in building construction. If your pots are straight-sided, this is a simple process of cutting strips of the foam approximately one or two inches wide and as long as the container is tall (for square containers cut solid sheets). You can lay out your strips and place a strip or two of cellophane or duct tape across the strips to hold them together. Wrap this insulation curtain around the container and fasten together with a piece of tape.
If your containers are conical shaped (larger at the top than the bottom), this process will be a bit more involved. You will need to make the strips wedge shaped, but keep the top end of your "foam wedges" only about two inches. Depending on the size and shape of your container, you may need to do a little experimenting here. After you have a shape that fits, put the pieces together in the same manner as above.
If you use the foil-lined foam and place the foil to the outside, you will gain even more insulating properties by reflecting sunlight. Dress this up with a simple curtain that complements your patio scheme. Follow the directions given above.
Insulate the inside of your container by following the instructions above, but do it for the inside of the container instead of the outside. To do this, either remove plant from its container (you may need to remove some soil from the root ball), place the foam strips or wedges inside around the container, and replace the plant. A better method, that doesn't require removing any soil, is to obtain a pot two inches larger than the original and line the inside with the foam. Unpot the plant and place it into the new foam-lined container and add soil as needed.
Polymer crystals?
The use of polymer crystals is one which is still being debated. For those who may not be familiar with polymer crystals (by a variety of names), they are a plastic compound that has the unique ability to absorb up to ten times their weight in liquid. Depending on the formulation, they can be formed to absorb only water or a variety of chemicals and not water. When dry, they look for all purposes like ground, clear to opaque plastic. When fully absorbed, they look and feel gelatinous and somewhat like gelatin. As the soil dries out, reportedly the crystals give up their water to the soil and help keep the soil hydrated for an extended period of time.
The use of these crystals has little to do with keeping a plants roots cool, however keeping the roots properly hydrated is the first step in keeping a plant cool. I do not currently use them and there is some debate as to a possibility of chemical contamination and excessive phosphates with some brands. In my experiments with polymers, I found no advantage or disadvantages. But there are many who swear by them and highly recommend them. There are an equal number who also swear they do no good and are another gimmick designed to get people to waste money.
I suggest that if you are interested, give them a try for yourself in your application and make the determination on your own. If you find that they reduce your watering chores, use them until you find reason to do otherwise. If not, don't waste your money otherwise. For me, polymer crystals are better for cooling neck wraps than soil amendments. But this is for another story, after my evaluation is complete.
Keeping your plants roots cool is a key consideration to growing the best container plants in the summertime. It is true that for some, summer container plants, while possible, are not practical because the heat of summer keeps us from our patios during times when viewing plants is best anyway. For these few folks, perhaps short-lived plants to delight us for a while and then are gone, may be the best answer. But, for the majority of gardeners reading this, our container plants delight us for all but a few short weeks in the middle of summer. Even then, we delight in them during the early morning and evening hours when we can appreciate them. We have presented you with a few ideas that I have used over the years for doing just that. I'm sure that you will have ideas of your own. To judge the success of your efforts, take before and after thermometer readings of the soil, this will be the best evidence of your success. Regardless of what method you use, your plants will appreciate your efforts and will reciprocate with better summer growth and color. To your success and your plants comfort. the "Hillbilly Gardener" |
