Parsley compliments the health of plants such as Asparagus. Parsley planted with asparagus seems to provide vigor to both as per Cornell University, as well parsley also acts as a repellent for the Asparagus Beetle . Hot and sweet pepper, tomatoes, eggplant are other vegetables that parsley has symbiotic relations with. It should not be planted near, or in rotation with lettuce or mint. Corn helps the development of parsley, but the parsley does nothing for the corn, nor is it harmful. [See: Companion Planting]
Soil ph should be between 5.5 and 6.5 for optimal results. They are tolerant of either Full sun or partial shade. A slow-release fertilizer to the soil at planting is advisable. Keep the soil moist, a shallow layer of organic mulch wouldn't be a bad idea as it retains moisture in the warm weather and insulates in the cool.
When mulching , don’t cover the crown of the plant so as to avoid the risk of rot. If you intend to grow it as a perennial, in the early Autumn you can promote new foliage by cutting the plants back and then set them out in the spring to await new growth.
Whiteflies are a serious pest of parsley, insecticidal soap or horticultural oil will generally eradicate this problem.
Caterpillars, worms, moths all love parsley and are frequent pests. The butterflies are attractive and useful as pollinators, but the larvae can be a nuisance [See:Worms and Moths in the Garden].
The parsley-worm also known as celery worm is a heavy feeder on its namesake parsley, the adult stage is the black swallowtail butterfly. Parsley worms will eat most of the plant.
Harvest And Storage
Harvest in the morning, after any dew has evaporated, or in the early evening under dry conditions is best. Gather stems and leaves as needed, start by stripping off the bigger outer leaves initially, later cut the parsley stems near the ground level. Periodic in season harvesting will serve to make the parsley plant grow bushier. Parsley can be dried or Frozen in much the same fashion as other herbs, but does not retain it's flavor as well. Fresh Parsley is best.
To Dry Parsley hang it upside down in a shaded well ventilated location. Drying trays or a food dehydrator will also suffice.