As warmer weather sets in and we spend more time outdoors, gardens and landscaping move up on our to-do lists, especially these days. Even the greenest of thumbs sometimes needs help — sometimes lots of it. Which plants to buy? How to plant them? Where to plant them? How to nurture them?

The best-run garden centers have the answers. They employ experts and — maybe most important — emphasize quality. Selling plants is not like selling power tools or lumber. Plants are alive, each one unique and each one vulnerable to disease, injury and death. Running a good garden center or nursery takes knowledge, years of experience, organizational skill, and a strong commitment to quality. And since most garden centers buy — rather than raise — most of what they sell, there is room for tremendous variation in buying ability and buying standards.

If you need help, nonprofit Washington Consumers’ Checkbook’s ratings of area garden centers for quality and price can help you find it. For the next month, Checkbook is offering free access to its ratings of area garden centers to Washington Post readers via Checkbook.org/WashingtonPost/garden-centers.

The opinions Checkbook collected from Washington-area consumers on garden centers reflect the big variation in quality among retailers. Some stores were rated “superior” overall by at least 80 percent of their surveyed customers, but several other retailers were rated “superior” by 30 percent or fewer.

Home Depot, Lowe’s and Meadows Farms scored, on average, lower than almost all the other stores.

But for the selection of plants they sell, these three big chains do very well on price. Checkbook’s undercover shoppers found Home Depot’s prices averaged 34 percent below the all-store average for comparable items, Lowe’s averaged 24 percent below the all-store average, and Meadows Farms’ prices averaged 12 percent lower.

Paying more for plants at garden centers does slightly improve your odds of getting better advice, service and product quality. Checkbook found that many of the stores rated highest for quality charge higher-than-average prices, but some stores that rate high for quality also have below-average prices.

For specific plants, Checkbook found enormous nursery-to-nursery price differences — perhaps more variation than in any subject Checkbook covers. For example, for a lavender in a six-inch pot, prices ranged from $7.99 to $25; and for a boxwood in a #3 container, prices ranged from $19.95 to $54.99.

Before shopping, make a plan. Consider your yard’s soil type, acidity, drainage patterns, and sunlight exposure, and match plant types with areas where they are likely to thrive. Your plan should show how your property will look right away, and how it will look years from now when your plants have grown. Without a plan, you could wind up with an assortment of plants that do not complement each other in size, shape or color. You might end up with shade where you want sun and with the view from or of your house obscured. And you might pay for expensive plants when inexpensive ones would do just as well.

Seek advice from gardening websites, friends with attractive gardens, and experts at local botanical gardens. If you want professional help, you can hire a landscape designer.

When making plant purchases:

· Check roots to be sure they have not dried out. Probe with your finger or look through the drain holes of a container to make sure the roots are whitish, not brown.

· For shrubs and trees, check for weak or broken branches. Bark should not have scars or holes, and pruning cuts should be flush with the branch or trunk.

· Check plants for insects, for browned or grayed areas or spots on leaves or stems, all signs of disease.

· In growing season, be sure there is new growth.

· Get a receipt that shows the common and the Latin names of plants and the size, number purchased, date of purchase, price and guarantee. You should also receive instructions on how and where to plant and on what pruning, feeding and spraying will be needed.

· Ask what guarantee you get. Fortunately, even though many plant deaths are the result of improper planting or care — in other words, the buyer’s fault — Checkbook found that most garden centers nonetheless offer broad guarantees.

Kevin Brasler is executive editor of Washington Consumers’ Checkbook and Checkbook.org, a nonprofit organization with a mission to help consumers get the best service and lowest prices. It is supported by consumers and takes no money from the service providers it evaluates. See Checkbook’s ratings of local garden centers free of charge until July 15 at Checkbook.org/WashingtonPost/garden-centers.

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