Containers filled with blooming flowers and bold foliage can bring a burst of color to a patio, deck or porch. And for some apartment and condo dwellers, containers may be the only way to grow.
The challenge is water. Plants in containers don't have room to stretch out their roots to search for water like plants in the ground do. To complicate matters, a plant's requirements for water change as the plant matures and the temperatures climb.
In the spring, when plants are just starting out, most containers typically need to be watered about every four days. (If you find yourself watering much more often, you should think about moving your plants to a larger container.)
However, in the heat of summer, with mature plants filling the container, plants might need to be watered daily.
To figure out whether you need to water, do the finger test: Stick your pointer finger into the soil up to the first knuckle. The potting soil should be just wet enough that some of it sticks to your finger.
Of course, you can buy a soil-moisture indicator at the garden center. Luckily, most of them work well. The simplest and least expensive of these are the clay figurines that turn darker red when the soil is moist, but turn orange as the soil dries out.
You also can buy potting soils and additives that help hold the moisture, but a good potting soil must balance water retention and aeration.
(Soil from your back yard holds too much water, and therefore allows too little space for air, when used in a container. That's why potting soils are essential in containers.)
Peat is the most commonly used ingredient in potting soils because it strikes that balance, but there are other ways to retain moisture and allow less frequent watering at the height of summer.
This waste product of the coconut industry holds more water than peat, but still holds enough air for plant roots. It's the primary ingredient in Miracle Gro moisture-control potting soils and Intrepid Coco-coir premium potting soil.
Water-holding crystals called hydrogels are supposed to absorb water, then release it as they dry out. However, there are a few drawbacks to these crystals. If you mix dry crystals into your potting mix, then water, the crystals can expand and push the potting soil up and out of the container. Also, while the crystals are very effective at absorbing water, research hasn't shown that they can reliably provide more water to plants than regular potting soil.
These little reservoirs look a bit like lollipops, with a globe full of water at the top attached to a narrow tube that's placed in a container. While they might not be pretty, water globes hold plenty of water and release it slowly. They can be a good way to water plants while you're on vacation -- as long as you're not gone too long.
Plants have pores on the underside of their leaves, through which they "perspire" and lose water. It's possible to block those pores, which stop plants from losing so much water, which, in turn, reduces the need for watering. Unfortunately, anti-transpirants work only for a very short time, sometimes less than a day. So, save your money and go get the hose.
Jeff Gillman, an associate professor of horticulture at the University of Minnesota, has written several gardening books.