A shortage of water is a good reason to let your garden go to pot

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Q: Are plants in containers more difficult to keep watered than plants installed in open ground? I have heard they are.

A: Here's the standard garden-expert answer: It depends. When planning for summer water conservation, plants in containers can be water-efficient or thirsty and demanding.

In my garden, I use containers for plants such as lettuce and other salad crops, summer annuals including petunias and big showy plants like fuchsias. They're an essential part of how I save water during summer because I group water-needy plants together rather than scattering them throughout the garden.

Here are some tips for conserving water for any summer, no matter what the water availability. Waterwise containers depend on several conditions:

• Container size. Logic prevails here. The larger the container, the more room for soil, roots and water retention for those roots. Think of how difficult it is to manage water in tiny little containers such as bonsai cups. Any container smaller than one gallon will rapidly fill up with roots and be more difficult to keep watered, especially if it's placed in direct sun. I like five-gallon sizes or bigger. Putting several plants in one large container improves ease of maintenance as well as appearance. If you are gardening with children, provide them with big containers. They'll be far less frustrated than with dinky ones that may seem "child size" but are hard to manage. A container as big as a half barrel can hold shrubs, fruit trees or a large tomato trained up a trellis.

• Container location. The more heat, exposure to sun or drying winds, the more water the plants lose. Also, some containers retain heat, particularly those made of dark materials like black plastic. If a black-plastic container receives direct sun, the soil temperature will rise, causing more water loss. Plants such as fuchsias require cool soil temperatures and can be killed by direct sun hitting a black plastic pot. In some cases, growing tomatoes, for instance, higher soil temperatures may be an advantage. To compensate for water loss, use a big container (15 gallons or above).

If a plant needs shady, cool conditions, place it where the pot will get shelter, especially from noon to about 5 p.m. Fuchsias like morning light and filtered light in the afternoon.

Hanging baskets dry out remarkably fast no matter what the pot material.

• Container materials. Some materials, such as soft terra cotta, will "breathe" in warm summer air and transmit water vapor. They dry out faster than wood or plastic. However, terra cotta pots are ideally suited for summer annuals such as nonhardy geraniums that like slightly dry, warm soils.

Plastic and other synthetic materials are available in every possible size and shape. They can be extremely expensive, as in large terra cotta "look-alikes" or very inexpensive, as in recycled nursery pots. Plastic doesn't lose water through the pot sides, but as noted above, it can become very hot in direct sun unless it's a light color. (Five-gallon paint or plaster buckets are easy to find and inexpensive. Latex paint stays on them for at least one season, so if you dislike the color, paint them. Then poke a bunch of holes in the bottom. This is the least expensive large container I'm aware of!) Plastic is easy to plant and easy to use, simple to move around a deck.

Beware of attached plastic saucers on the bottom of pots. It would seem that they might make watering easier by holding excess at the root level and allowing the plant to draw it up when needed. The fact is that a layer of water at the bottom of the pot will tend to cause root rot, particularly on susceptible plants such as amaryllis and African violets.

If your plant has a saucer built in, give it a tug to release it from the pot. You can set the plant on it, but be sure to dump any accumulated water off into another plant rather than allowing it to sit around and make soggy roots.

Wooden containers breathe a little but don't heat up and don't dry out much. They suit Northwest gardens and are readily available in many sizes. However, if you have a wood fuchsia basket in full bloom around Mother's Day, be aware that it will be full of roots supporting that huge flowering plant and may become root bound by June. Fuchsia baskets require frequent watering, especially if they are in hot spots. Give them shelter and water from the bottom by taking the basket down and setting it in a bucket of water. Allow it to take up the water fully, then drain and hang. It's common for hanging baskets to dry in the center and have water just cascading down the sides and being wasted. Take them down for watering if you have any thought that they might be root bound, especially if they wilt in late afternoon.

Stone, concrete and similar heavy materials retain water well. They are frequently impractical because they are difficult to site and impossible to move, but if you have a spot where they will be relatively permanent, these are good choices for waterwise containers. A built-in planting bed, like a brick planter box, is perfect for the waterwise garden.

• Planting tips. When potting, fill the entire container with potting soil. The idea of putting gravel or stones at the bottom has been disproved; it tends to make water management harder by causing water to rot roots.

• Type of potting soil. Here the waterwise discussion gets a bit tricky. Why don't we all just dig up garden soil and toss it into our containers? Because garden soil tends to pack down and become compacted when watered. This reduces the amount of oxygen available to plant roots. Roots need, ideally, a potting soil that provides 50 percent solid materials, 25 percent retained water and 25 percent air spaces (you can't necessarily see these percentages by staring at the mix.) Too little air space, too much water, or too little water, and the plant dies.

Potting soils vary in their ingredients. Be sure to get those with pumice or perlite or other gritty ingredients to allow for good drainage. If the potting soil seems to be "sticky" or "gummy" without pumice or other particles that allow water to drain, add bagged pumice or perlite to it. Drainage is the key property in the success of plants in containers.

What about potting soils advertised as "water retentive"? For several years gardeners have been able to buy an artificial granular material that poofs up into a Jello-like substance when wet. It's added to potting soils and is expected to help with water saving by releasing water back to the plants.

Research on the original materials done several years ago indicated that plants did not grow better with it (and soils with it added are expensive). In the past year, the material has changed somewhat and may now be more workable for plantings. I know some greenhouses that find this material useful for hanging baskets, and this may be the best way to use it. It's certainly too expensive to scatter about in open gardens.

Screened compost, or a bag of commercial compost, can be a valuable addition to potting soil. Small particles of compost retain water just as the artificial materials are reputed to do. For my potting soil, I add 25 percent by volume in compost to the materials I buy and skip the artificial material. Again, concentrate on the gritty components because drainage is vital.

• Plant selection. Obviously, some plants will do better in hot, dry situations. Herbs, greenhouse geraniums (the nonhardy type) and sedum, as well as grasses, are perfect for containers that will be exposed and somewhat dry. All of these resent too much water.

Fuchsias, begonias, impatiens, ferns and petunias require regular watering to do their best.

If the container, the site, the potting soil and the plants are properly considered, container plantings can be terrific parts of the waterwise garden.

Clarification: Gwen Stahnke, turf agronomist for WSU Cooperative Extension, adds the following to the discussion of lawn care published April 1: WSU specialists do not recommend using Weed/Feed products, except when weed infestation is severe, and then it should be used only once a year. If weed infestation is not severe, it is better to separate weed control from fertilization.

For updated lawn-care tips, see Stahnke's Web site: www.puyallup.wsu.edu/turf.

Mary Robson is area horticulture agent for Washington State University/King County Cooperative Extension.