To brighten our drab winter days, Mother Nature sent us brightly colored, juicy fruits called citrus. Those luscious round orbs of yellow, orange and green are reaching their peak for picking.

Originating in tropical and subtropical Southeast Asia, citrus plants can be trees or shrubs. The juice contains high quantity of citric acid, which gives the fruit its sharp flavor.

Besides enjoying the bounty of citrus at this time of year, we asked Colby Eierman, director of gardens at Copia, for hints on citrus maintenance now and in the near future.

"It's harvest time, but it's also time for frost protection," said Eierman. "There are a few products on the market for frost protection. The two products we've used successfully are Remay floating row cover and Tuff Bell floating row cover, which lasts longer, but costs more."

Floating row covers are so named because they are draped and gently float over crops as they grow. Eierman recommends building a frame, such as a teepee, to keep the row covers off the foliage.

"Another product that people have used is a spray, Cloud Cover is one brand, that gives a few degrees of protection. We don't have a lot of experience with this product, but we understand it's important to re-spray, especially after rainfall. An additional fun way to protect citrus from frost is with little holiday lights. Keep them on all night and the plant will stay warm."

After the fruit has been harvested, it's time to prune. While pruning time will be different depending on the variety, usually pruning occurs by March, when the coldest weather has passed.

Talking of the current cold snap the valley experiencing, Eierman said that if trees or bushes do suffer from frost damage, "wait until new growth appears before you start to prune."

Are there any tricks to pruning citrus?

"I look at the structure of the plant and decide what size and shape I want it to be," said Eierman. "Citrus is not as particular about pruning as apple or pear trees."

After pruning is complete, Eierman and his crew spray the citrus plants.

"Spray after pruning because you have less to spray and better access to all of the plant. We spray to control scale and white fly. What we use is dormant oil mixed with the acting agent pyrethrin, which is an organically derived insecticide from the chrysanthemum flower."

Pyrethrin is known to be the safest insecticide to use around food. However, it can irritate eyes, skin and respiratory systems and is harmful to aquatic life.

"Plants should be sprayed ideally on a cloudy dry day because you want the organic spray to stay on the plant as long as possible," said Eierman. "We've found other insecticidal soaps to be effective, too. Anything that is a fine mist that will get into the tree. It's always a good idea to wear a respirator and keep your skin protected."

Eierman also protects the plants from insects by using a product called Tanglefoot Pest Barrier.

"You paint it on the base of the tree and it keeps ants out of the plant. Ants bring aphids and scale."

After pruning and spraying, it's time for fertilizing.

"Work organic, pellet type fertilizer a few inches into the soil. The NPK rating (nitrogen, phosphorous and potassium) should be heavy on the nitrogen, so something like 3-2-2 or 5-1-1 would work. You can buy a citrus or avocado specific fertilizer. Iron, zinc and magnesium are also good supplements. A lot of times you can bring around failing trees with the right fertilizer. We generally fertilize spring, summer and fall, but if a tree is suffering, we might feed it the first of every month."

Eierman thinks people should experiment with planting different types of citrus, most of which are self-pollinating. Citrus thrive in full sun, facing south. Several varieties will tolerate less sun.

"We have types that are happy with five to six hours of sun. An easy starter plant is a Meyer lemon. They can be grown in containers and are frost tolerant. They have a rewarding lemon flavor. We find that the sweeter and larger citrus, such as grapefruit and larger oranges, can be finicky. Usually, smaller and less sweet grow easier."

Watering should be consistent and not too wet. Citrus prefers less frequent and deeper watering, similar to tomatoes. The soil surface should dry out between waterings and not have a boggy consistency.

"Watering is more important than people realize," said Eierman. "In drought conditions, the plant drops flowers from stress. If you have curling yellow leaves it probably means the ground is too wet."

All in all, Eierman is pleased with the success of the crop at Copia. "This was a good citrus year," he concluded.