Tips for outstanding container success

By Melanie Mathieson
Gardening Guru

I have six large black planters lining my driveway on my property in Thunder Bay. For the last three summers, the plants in them have taken over and produced a profusion of blooms. I had never given the results much thought until the compliments and enquiries started to add up, so here is a column with some tips so that you get the same results.
We cannot do much about the summer temperatures but we can sure manipulate the other conditions necessary to grow fantastic flowers in containers. Here is list of some of the things that you can do to really get that green thumb working.
There are many important tips to consider here but you must begin with choosing appropriate containers. In previous columns, I have indicated that almost any container can be used for plants. I am not changing that statement but if you want to produce an excessive sized profusion of plants and blooms then you must choose a large container. You can still choose containers with an aesthetic purpose but to really produce an explosion of blooms you need a large container because the plants need a generous amount of soil to grow to excessive proportions. The large volume of soil is required for support of the plants (roots growth) and to provide nutrients and moisture. The planters that line my driveway are 15 and 30 gallons. They are large but they produce unbelievable results. I have other containers on the property that are not as large and although successful in producing large crops of herbs and flowers these containers are used for other purposes and expected results.
The colour of your container may be important too as my planters are black. Black and other darkly coloured planters heat the soil which in many cases is beneficial for the plants. Now in some cases when the moisture and amounts of soil volume are not adequate, these dark coloured containers can kill the roots of the plants causing the plants to die. So you want to be careful here in choosing the colour of your container. If you feel you can provide ample soil volume and moisture in a dark container then choose a dark colour, if you are leery then choose a lighter coloured container. Also make sure your container has drainage holes or is a material you can drill through to make holes.
The next important part is the soil. I purchase a high quality soil-less mix formulated for planters. You can purchase soil-less mix at most garden supply centres in the spring and throughout the gardening season. I always purchase some in late summer just to be ready for the spring. Read the bag to compare features of each brand and then choose the one you feel is the best quality. When filling large containers I always use woodchips or bark to fill the first 1/3 of the container and then top with soil. This allows for adequate drainage, uses less soil and makes the pots a bit lighter if you have to move them.
It is important to choose the right plants for the location of your pot. I like plants with big impact and try to think outside the box by choosing plants that may be less traditional for containers. Last year I chose cosmos to plant in the middle of the planter for some height to act as my “spike”. Well that experiment resulted in some really unexpected results. The cosmos took over the container and choked out all of the other plants I planted. They ended up growing to be over 5 feet tall. Many passerbys mistook them for shrubs planted in the containers until they bloomed then many didn’t know what they were as they had never seen cosmos that tall. So much for my 24 inch spike! This year and two summers ago I planted wave petunias and the results have been outstanding. Snapdragons, Gerbera daisies, ornamental grass and liquorice root are also great choices for planters in the full and hot sun. These planters are in hot, full sun the entire day so I choose plants that are very heat and sun tolerant. It is very important the location of your planters in mind when choosing the plants. For the most success choose the plants that will tolerate your conditions the best. There are many other choices of plants for shade and partial shade too.
Another important step in adequate care for planters is food. Planters need regular fertilizing. I like the new “shake and pour” products on the market. I use this granular product once a month during the growing season. I am finding great results from this product but there are other great fertilizers available in powder and granular form or water soluble formulas. Just pick a product with a high middle number which is phosphorus (10-30-10 for example) and use it according to the directions for containers. Never over fertilize, as it will not yield the results you want.
The most important of all of these tips is adequate watering. You cannot neglect this step ever. Do not let your containers get bone dry. This stresses the plants and prevents continuous growth. After a few times with dried out soil, your containers may be done for the season especially when the plants are due to bloom. If you feel you cannot provide a regular watering schedule then maintaining container gardens is not for you. I water my containers no less then every two days but they are checked everyday in hot weather to see if more water is needed. Due to the large size of the container and the soil-less mix with moisture holding gel beads this is all my containers need. Your containers may need watering on a daily basis or twice daily when it is really hot and dry. You must check regularly though as the plants grow larger they require more watering. When I water my planters I use a rain shower attachment for the hose and stand at each planter until the soil is thoroughly soaked though and water starts running out the bottom of the drain holes of the pot. A small watering can of water everyday in a large planter is not enough moisture. Be generous with the water and you will see the results.
Follow these tips and you will have the best container flowers on the block.