Joan Caswell has just about had it with zinnias. For several summers they've been yellowing, losing their leaves and dying. This is not reputedly a difficult flower. So Caswell, of Medford, stopped by the plant clinic at the Master Gardener Association's Spring Fair at the Jackson County Expo for some diagnosis.

Joan Caswell has just about had it with zinnias. For several summers they've been yellowing, losing their leaves and dying. This is not reputedly a difficult flower. So Caswell, of Medford, stopped by the plant clinic at the Master Gardener Association's Spring Fair at the Jackson County Expo for some diagnosis.

"It's usually better with bedding plants to get the smallest you can get," Master Gardener Marsha Waite says. "And get them without flowers."

As the plants grow, Waite says, the roots remain confined to those little trays, and when you put the plants in the ground, the roots aren't developed enough to support the plants.

"What's progression of the disease?" she asks Caswell.

This leads to a discussion of soil testing, transplanting and other garden lore.

The free plant clinic may not be the major attraction of the annual garden event — that title probably goes to the veggie and flower starts avid gardeners snap up by the thousands — but it's somehow close to its essence. After all, this is an event at which people wander around in T-shirts bearing sayings like "DIRT FIRST."

Art Davis has bought a wicked-looking weed. The verdict: crabgrass.

"Be glad it's not Bermuda grass," volunteers tell him.

"How do you get rid of it?" the Shady Cove man wants to know.

"Hand-pull it," Waite says.

Davis says he applied a pre-emergent weed killer in March. Lawn-care product companies typically recommend applying pre-emergent in the middle of March. But Waite says in the Rogue Valley, which often has a stretch of spring-like weather in late winter, it's best to do the pre-emergent treatment in mid-February.

Caswell wants to know if it's too early for zinnias. Waite says it is. She says to put them in individual pots and begin exposing them to east-side sun, half-an-hour or so more each day.

Waite, Wendy Purslow and Carol Robinson field questions on bugs, incense cedar rust and the usual troubles with rhododendrons and azaleas. Rhodies do spectacularly well in the Willamette Valley but are a challenge locally, wanting filtered shade, lots of water, acidic soil and plenty of oxygen at their roots.

Elsewhere, people stroll the floor of Compton Arena buying veggies, flowers, herbs and more, some pulling wagons in which to stash their green swag.

Joan Long, a master gardener from Medford, is testing people's well water for nitrates, which come from manure, chemical fertilizers, septic systems and even decaying vegetables. When she adds a reagent, the sample will turn red if nitrates are present, the redder, the worse.

"If you get down in there," she says, pointing to the area of 10 parts per million on a scale, "it's recommended you have more testing."

Up to 2 ppm is considered natural; anything over 10 ppm should be tested by a certified laboratory such as Nielson Research Corp. in Medford, Long says.

A high level of nitrates may cause a type of "blue baby" syndrome and has been linked to miscarriages and gastric cancer. Nitrates cannot be removed by water softeners or boiling. To get rid of them you're talking distillation, reverse osmosis and ion-exhange systems, which are expensive.

Joell Stine, of Talent, is providing another type of water information. Stine, who works for the Medford Water Commission, is staffing a sprinkler system information booth. Often, she says, the problem isn't too little water but too much.

"It's difficult," she says. "People move into a house with a sprinkler system, and they have no idea."

She or fellow workers will come to water-customers' homes, do some measurements and help people set up timers for efficiency. The best part is, it's free.

"There's a big difference if the system has rotor heads or spray heads," she says.

A system that puts an average of a half-inch of water in measuring cans in 15 minutes needs to be run in the summer for 28 minutes at a time, twice weekly. Stine also suggests the footstep test. If the grass springs right up, you don't need to water. If it stays bent, water.

Another attraction of the fair is the free classes that go all day Saturday and Sunday. Ellen Scannell is teaching one on culinary herbs, which it turns out can be distinguished from spices by taste, usage and geography. Spices are pungent, prized for their seeds and bark and originate in the tropics. Herbs are subtle, used for their leaves, and come from temperate zones.

In addition to being yummy, herbs can be used for dyes, repellents, toiletries, landscaping and drawing bees. They are forgiving, and not a favorite of deer.

The fair has lots of vendors, too. Kitty Bertlin is selling an active composter that fits under the sink and plugs into a standard outlet. She says it will turn 120 pounds of table scraps into finished compost, gardeners' "black gold," in two weeks. Compost happens (as they say) inside a chamber. A fan draws air to the heap, and a carbon filter prevents odors.

The units sell for $290. A pet poop unit goes for $390. Where else are you going to find something like that?

The fair continues from 10 a.m. to 4 p.m. today, with classes in composting (11 a.m.), lavender (noon), tree planting (1 p.m. ) and, for the kids, frogs and toads (2 p.m.).

Reach reporter Bill Varble at 776-4478 or bvarble@mailtribune.com.