Garden centers aren’t the only places to buy green things; various websites and catalogs sell plants by mail. But should you deal with them?

There are two main advantages to buying this way. First, plants can be less expensive (even including possible shipping costs). Second, catalogs and websites may sell unusual plants unavailable at local nurseries.

But there are big downsides to ordering by mail or online. First, you usually get bare-rooted plants, which can be planted only during the dormant season (before tree buds begin to swell). Second, you usually can’t get larger plants. Third, if you are dissatisfied, it’s a hassle to repackage growing things and send them back. Finally—and most importantly—unlike when shopping in person, you can’t see exactly what you will be getting or select particular specimens. The plants you get may bear little resemblance to the beautiful pictures in a catalog or on the web.

If you order plants, choose companies whose catalogs or websites provide the most precise and detailed descriptions. Catalogs that use only age to describe a plant’s size and fullness leave much to be desired. For a large directory of online sellers, along with customer reviews, visit the Garden Watchdog section of Dave’s Garden.

Keep these tips in mind, too:

Be prepared. You’ll need to plant the merch shortly after it arrives. Make sure the planting site is set, and have mulch ready, along with needed fertilizers.

Don’t leave plants trapped inside their packages for very long. Open them right away, and put the plants in a protected and shady place until planting time.

Read carefully. Because nearly all mail order plants are dormant, you won’t really know if they are healthy until growing season begins. Look closely at the company’s guarantee and return policy.

Be patient. Photos in catalogs and online usually showcase mature plants at peak bloom. Yours may take a couple years to get there. Plus, most perennials won’t bloom the first year.

Many catalogers automatically substitute another plant if the one you ordered is out of stock. If you’re not interested in a substitution, make sure to state that clearly in the order.

Become a Smarter Consumer Get free, expert advice delivered to your inbox every Wednesday when you sign up for the Weekly Checklist newsletter.