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Gardening with Allen: Container plants need special care

The Columbian
Published: May 31, 2018, 6:05am

Can you help me figure out what I am doing wrong with my tubs and hanging baskets? They are never as big and beautiful as my friends’. The ones I plant myself don’t fill in completely. Even the ones I buy already fully grown deteriorate after a month or two. I have good success with the flowers I plant in the ground. What am I doing wrong?

Yes, container plants do have different growing requirements than plants in the ground. When soil is placed in a container it holds twice as much water after draining. This leaves less room for air space. Roots need air (oxygen) as well as moisture to thrive.

Potting soils are made with coarser materials so there are larger spaces for air holes. Potting soils vary in quality. Some do not drain well enough for good growth. The best potting soils are made with peat moss, vermiculite and perlite or sponge rock. These materials are light in weight and have lots of air space as well as holding plenty of moisture. Sand and bark dust are often used in potting soils. Sand often contains finer silt and clay particles which reduce air-holding capacity. Bark is OK as long as there is also some peat or vermiculite or both.

Containers must be watered more frequently than garden plants. When water drains through them it dissolves fertilizer, which is lost with the drain water. It sounds like your plants are suffering from a shortage of fertilizer. Container plants need a lot more fertilizer than plants in the ground. Liquid fertilizer can be applied every time you irrigate or at least once a week using rates recommended on the fertilizer container.

I prefer slow or timed-release coated fertilizer such as Osmocote. Fertilizer particles are coated with a porous layer which allows water to seep through. The water dissolves a little fertilizer and flows back into the soil. Coated fertilizers last four to eight weeks. I usually apply Osmocote about once per month. Even if there is some fertilizer left in the coated pellets, its release rate has gone down.

Container plants are usually watered every day when they are fully grown. They will need less frequent irrigation if moisture-holding crystals are mixed into the soil before planting. Several brands are available which retain extra water without reducing soil air space. If plants are allowed to get too dry and wilt frequently, they will not be as healthy and attractive. As long as you have a good soil mix, it is hard to over-irrigate.

When planting your own containers, place plants so the soil balls are almost touching. Larger plants will fill in more quickly.

Flower varieties in containers need to be selected for their light requirements. Fuchsia, impatiens, begonia, coleus, lamium, browallia, lobelia, nierembergia, and variegated ivies grow well in the shade. For sunny areas, some of the most popular flowers include diascia, petunia, ivy geranium, lobelia, brachycome, bidens, nemesia, pansy, bacopa, calibrachoa (Million Bells), alyssum, trailing snapdragon, trailing verbena, lotus, and sweet potato vine.

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