Q: Can I trim and shape my globe evergreen bushes and if so, can I do it this spring? They’ve been in place a number of years and do have dead branches inside. What would you suggest for trimming back? — Bob L.
A: Your evergreens appear to one of the dwarf cultivars of arborvitae, which remain as low-growing mounds, making them good choices below your window. Non-dwarf forms of globe arborvitae can become quite large, forming basketball-shaped shrubs 7 feet high and wide if left untrimmed.
Your arborvitae cultivar will remain short, but pruning can help balance uneven growth. Your shrubs appear to be in good health, and it’s normal for arborvitae to have bare stems on the interior.
When pruning evergreens, it’s important to remember they aren't capable of being cut back and rejuvenated like deciduous shrubs. Stay within the zone of healthy foliage. If we cut back into bare branches, those branches normally will not sprout new growth. With arborvitae, that usually means working within the outer 4 to 10 inches of the shrub, depending on its age and size.
Dwarf arborvitae tend to grow lopsided, and trimming can help round them out. Tight shearing isn’t recommended, but if the small, uneven outgrowths are selectively pruned away, the shrubs will maintain a neat, but natural, appearance.
Arborvitae are very flexible in pruning time. May and June are recommended, and trimming can be done throughout summer until early August.
Q: What mixture of soil do you use in your own outside flower pots? — Marie N.
A: My wife, Mary, and I, usually use Miracle-Gro Potting Mix, straight out of the bag. Plants grow well, it contains slow-release fertilizer, and it’s available almost everywhere. I also highly recommend the potting mixes that you find at independent, locally owned garden centers. They often sell a similar blend used in their own greenhouses, which is a great endorsement.
There seems to be no national criteria or regulation of potting mixes, potting soils and their ingredients. I always steer clear of heavy, cheap potting soils.
Can you reuse potting mixes in outdoor containers? Mary and I have reused high-quality mixes for five years or more with fine results. We remove about a fourth of the old, add fresh, and add slow-release fertilizer granules to recharge the fertility.
Q: In a recent column about houseplants, you mentioned a product that is sprinkled on soil of houseplants to control bugs. I cannot find the article and was wondering if you would tell me the name of it again. Thank you. — Suzanne. M.
A: There are two different products that can be added to houseplant soil, depending on the insects present. One product is Mosquito Bits, which the label indicates is also used to control fungus gnats, the little flack flies that flit around houseplants. The product is sold at garden centers, hardware stores and national chains. The granules are applied to the soil, where it breaks the life cycle of these annoying small flies at their larval stage.
The other product I've mentioned is systemic houseplant insecticide granules, which can control insects like spider mites, aphids and mealy bugs. The insecticide is added to soil and taken up by the roots, and it protects the plant internally as insects suck plant sap. The product can be found at most garden centers.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at email@example.com. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.