Conifers include a wide range of trees and shrubs, most of them evergreens. They reproduce via pinecones. The name conifer is Latin for "cone-bearing." Although conifers generally are hardy and strong plants, weeds pose a serious threat. Weeds that compete with the seedlings for space and nutrition will win. Weeds compete with conifers at all stages of growth and also in the winter for food and sunlight. Select herbicides that are the most efficient, and pay close attention to weed control.
Before you plant conifers, prepare a good site by applying post-emergent herbicides to the area to get rid of any established weeds. A post-emergent herbicide attacks weeds after they appear. Other types of herbicides called pre-emergent destroy weed seeds' ability to sprout. A problem with pre-emergent herbicides is they often leave the soil unusable for a long period before it can be replanted. The most common and effective post-emergent weed killers are Roundup; Garlon; 2, 4-D; and Roundup Pro. They are easy to apply and safe when used as directed.
Sterilize the Soil
To sterilize the soil, use a tiller to a depth of 6 inches. Work out all clumps, and get rid of any debris such as uncomposted leaves. Soak the bare soil with fumigant spray. The best time to fumigate soil is in the fall when soil is warm and moist but not overly wet. The tricky part in fumigating soil is obtaining the perfect soil climate. Too wet, and the fumigant will wash off too fast, and some weed seeds will escape treatment. Too dry, and weed seeds will survive the treatment. The best fumigants for conifer beds are dazomet, metham and methyl bromide. They release a gas after application that permeates the earth and destroys seeds.
After you plant conifer seedlings, get rid of any new weed shoots by hand to avoid hurting the young shrubs and trees. If weeds get out of hand, you may still need to use a herbicide. Using herbicides in a seedbed for growing seedlings is tricky. The herbicides that do have label directions for use in seedbeds often have restrictions or work well only with certain types of conifers, so always read the directions thoroughly before application. Be aware that herbicides good at one stage are not necessarily good at another. Roundup is great to prepare a seedbed but can kill seedlings on contact.
Some of the possible herbicide treatments for seedling conifers are Devrinol 50 WP, Pennant 7.8 EC, Ronstar 2G, Stinger and Goal. Pay close attention to what weeds each type kills. Apply a combination of weed killers where needed to kill all varieties of weeds.
Adult conifers are extremely hardy and have fewer problems with weeds due to the mass of the plant. Typical conifers produce a large amount of dense shade that keeps most weeds at bay, so herbicides are rarely necessary at this stage. However, remember that conifers take as long as two years to attain full growth and until that time are vulnerable to weeds.
Always take care to protect yourself when using herbicides. Wear long-sleeved shirts and long pants. Use goggles to protect your eyes, and wear a breathing mask so you do not breathe in fumes from the sprays.