Weekend gardeners who work in air-conditioned offices or homes all week may get hit hard by summer heat. They just aren't used to it.

"Gardeners need to be in good shape for the heat, just like athletes," said Wayne McLaurin, a horticulturist with the University of Georgia Extension Service.

The human body needs time to adapt to working in the heat, whether you're running a marathon or weeding petunias. And you can't rush the process.

"The body needs to adapt to levels of work and heat," McLaurin said. "As it adapts, it improves the stability of the circulatory system and the balance of salt in the body. Don't assume if you're physically fit, you can work in the heat easily. But you should adapt more quickly than those who are out-of- shape."

When you're used to the heat, your body temperature and heart rate rise less and you sweat more. You may not necessarily work better at higher temperatures and humidities when you're used to it. But you'll be able to work in heat you would otherwise find intolerable, McLaurin said.

"When the body becomes overheated, less blood goes to the active muscles, the brain and internal organs," McLaurin said. "You get weaker, become tired sooner, you're less alert and your judgment may become impaired."

As strain from heat grows more severe, your body temperature and heart rate can rise fast. Workers may not realize the problem because they feel no pain. But a 2-degree rise in body temperature can affect mental abilities. A 5-degree increase can cause serious illness.

"Tailor your acclimatizing period to suit the type of work, the clothing, the worker and the climate," McLaurin said. "A gardener can start working in the heat for around two hours with a break after the first hour. Moderate to heavy work will require a shorter work period."

Use common sense when you're working in the heat. Some things to remember:

* Make sure you drink enough water to replace body fluid lost through sweating. Your body can become overheated long before you feel thirsty. Water or fruit juices replace fluids quickly.

* Gradually adjust to working in the heat.

* Take breaks in a shaded or air-conditioned place whenever you can.

* Check the temperature and humidity at least hourly and monitor your response to the heat.

* The danger of heat stress increases with higher temperature and humidity and with direct sunlight.

* Design your work so you can do one task in the sun and the next in a shady place if you can.

* Younger, well-rested and physically fit workers are less likely to suffer heat illness than other workers. But even workers in good shape can become seriously ill from heat.

* Many drugs, including alcohol and cold and allergy medications containing antihistamines, increase the risk of heat illness. Check the label for sun exposure information.

"When the temperature climbs to 95 degrees, restrict your gardening to 40 minutes with a break of 20 minutes," McLaurin said. "And take advantage of a garden bench. Many people work so hard growing things but they forget to sit down and enjoy the beauty."