I’m wondering when is the best time to prune my Oregon grapeholly? It is a standard-size Mahonia, not a compact variety. It’s so pretty in bloom, but it needs trimming – if I do it now I’ll lose all the berries. If I trim it in the fall, will I lose the spring blooms? I hesitate to prune in fall because of the browning that occurs over the winter, which already takes a fair amount of leaves. Please help!

Sometimes in gardening, as in life, we find ourselves between a rock and a hard place. So it is in deciding when to prune your Oregon grapeholly (Mahonia aquifolium). As you’ve discovered, cut back this evergreen ornamental shrub in early spring and the slightly-fragrant, pyramidal-shaped cluster of bright yellow flowers won’t emerge during their typical April to May blooming time. Prune this shrub in early summer and there won’t be any of the bird-attracting, grape-bunched, chick pea-sized, blue-black berries in late July.

You must, however, prune to keep this vigorous-growing ornamental (it can reach nine feet) looking tidy. If you’re willing to sacrifice the flowers or the berries for a season, you can hard prune any time of the year, except early autumn. If you prune in September or later, the new growth that will be stimulated may not harden off before the killing winter cold. On the other hand, light pruning (cutting back one stem in three) in early summer will preserve most of the flowers and/or berries.

In terms of cultivation, if many of the lustrous green, leathery leaves die during the winter, perhaps your Oregon grapeholly needs to be moved to a different site. Hardy to zone 4, this native of the Pacific Northwest likes moist, well-drained, acid soil in a protected location; it doesn’t like exposure to excessive heat, dry soil, and desiccating winds.

How you can tell a male kiwi plant from a female kiwi plant?

Kiwi plants are dioecious, meaning that male flowers occur on one plant, and female flowers on another plant. One sure fire way to know which you have is to observe which plant bears fruit; that most certainly will be the female plant.

However, not having fruit does not guarantee that you have a male plant, as many factors can prevent fruit from forming on a female kiwi in our Michigan climate. The truly scientific method of determining male or female is to use a hand lens to inspect the flowers. A male plant will have flowers that have no stigmas, or have undeveloped stigmas. A female plant will have flowers with ovaries that are prominent and with stigmas, but without stamens. If you do not have a diagram of flower parts and actual flowers to inspect, the best approach with a kiwi is to purchase your plants from a nursery that has identified the particular plant as male or female. Be sure to grow at least 1 male plant for each 8 female plants in close proximity to ensure fruiting.

If you have the opportunity to visit the 4H Children’s Garden in East Lansing on the campus of Michigan State University, be sure to see the large and vigorous hardy kiwi on a large, sturdy trellis in the amphitheater garden area. Sorry, I don’t know whether it is male or female, so take a hand lens with you if you visit while it is blooming this spring. For a virtual tour of the 4H Children’s Garden on the Internet go to http://4hgarden.msu.edu.

I heard someone say they made a 50/50 blend of soilless potting mix and regular garden soil for a container planting. Why would this be done and for what types of plants?

A 50/50 blend of soilless potting mix and regular garden soil is fine as long as you can control the amount of water the container will get. Garden soil will retain moisture for longer period of time which can be helpful with smaller containers or hard-to-water areas.

The negative is that we cannot control the weather, so during the summer when we might get a few rainy days in a row, you could easily end up with root rot.

A straight soilless mix does dry out faster, therefore more frequent watering is needed, but you have a far less chance of overwatering and your plants will root out much faster.

I’m thinking about growing dahlias this season. What are their cultural requirements (soil, sun, etc.) and how do I overwinter them?

Dahlias are not only beautiful, but they are also extremely easy to grow. They require at least 6 hours of direct sun a day and enjoy a well-drained, light soil mix. Dahlias can also be grown successfully in large containers for your porch or deck. Like any large-flowered annual, deadheading is important throughout the season, as well as fertilizing every third watering with a water soluble 20-20-20 fertilizer to keep your dahlias blooming all summer.

When the first light frost kills off the top growth, simply dig up the tubers, remove all foliage and stems, wash off any excess soil, and allow to dry on newspaper for a few days. It’s a good idea to dust with Bonide bulb dust to help keep them free from disease. Cover the tubers with dry sphagnum peat in a paper bag or box and store in the basement for the winter. For best results, the bulbs should maintain a 50 degree temperature at all times.

Are tomato plants supposed to be pruned?

A light pruning can be done on tomatoes to help yield more fruit and extend the growing season. Understand though that pruning is not just cutting away at the plant anywhere! Only prune the suckers away from where the main stem and the branches meet.

The disadvantage of pruning is the lack of foliage to help shade the fruit which protects them from sun scald.

To achieve the early fruit and keep enough foliage for shading, prune suckers from the lower 14 to 18 inches of the plant and let the rest of the tomato bush out and produce a bountiful harvest.

I want to plant cannas in containers this year. What type of soil should I use? Do cannas need to be constantly moist and, if so, should I plug up the drainage hole in the container?

Although cannas are water-loving plants and actually do very well in a pond or water garden setting, they adapt very well to containers.

Use a soilless mix of sphagnum peat and perlite. Select a container large enough to support your canna. Most cannas will grow between 36 and 48 inches tall. A 14 inch or larger pot should work well. Also think about planting other shorter or trailing annuals in with your canna to help balance the overall look of your container garden.

Water only when the soil is dry but realize with growth your canna will dry out quicker and probably require a daily watering. Do not plug the drainage hole. All it takes is a few rainy days in a row to fill the pot with water and ruin your plants.

I would like to grow herbs, but I have partial shade conditions. Are there any herbs that will grow in partial shade?

Most herbs can be grown in 4 hours of sunlight (part shade), but realize the plants will stretch for the sunlight and could become “leggy” looking. A constant pruning will help keep the herbs full and healthy, so the more you use your herbs for cooking, the better off they will be.

I have had trouble growing tomatoes near a walnut tree. The tomatoes do get 4 or 5 hours of sun daily. I have heard that it can be difficult to grow things near a walnut tree – is that true? Could that be the problem?

It is definitely true that it is difficult to grow certain plants under black walnut trees. All parts of a black walnut tree contain a substance called juglone which affects plants growing beneath and around the tree. Different plants have varying levels of tolerance to being planted by black walnuts. Unfortunately, tomatoes are probably one of the worst plants to plant around this particular tree. Some fruits and vegetables that have more tolerance to black walnut trees include: lima beans, snap beans, beets, sweet corn, onions, parsnips and black raspberries. One option would be to try growing your tomatoes in a large-size container in order to keep them out of the same soil as the roots of the tree. Be sure to get a bush type tomato which will not be as aggressive and overtake the container.

We have had a Wisteria sinensis (Chinese wisteria) for about 4 years. I have been shaping it into a umbrella-shaped tree and it has been growing well, but has failed to bloom for us. I read that I should cut the roots, so we have done that and still no blooms. It is located where it receives morning shade and then sun from noon on. Can you give me some ideas to try to make it bloom? Also what time of the year should it bloom?

Wisteria sinensis (Chinese wisteria), along with any other wisteria, may often prove difficult to flower. The tree and vine forms both require a site with full sun as well as a well-drained soil. Wisteria also need to be planted in a protected area as winter winds may kill off any flower buds. Little, if any, nitrogen fertilizers should be used since they promote leafy growth and inhibit flowering. Instead, use a fertilizer high in phosphorus. Heavy pruning should be done only in June, after normal flowering should have occurred. Very rarely does Chinese wisteria bloom on new growth, meaning a fall or winter pruning would remove potential buds for the next flowering season.

“Root pruning” is a technique used to stress the plant into producing a bloom. This technique is best done in May or June, after the flowering occurs. Use a sharply pointed shovel to make the slits, which should form a circle around the tree at a diameter of two feet for every inch of stem diameter. Be patient, as it sometimes takes two to three seasons for root pruning to be effective.

Another tip is to always purchase named cultivars, rather than seed-grown stock. The cultivars tend to produce better and more reliable blooms.

We have 2 hanging baskets on our patio—one a fuchsia and the other geraniums and ivy. Birds go from one to the other to make a nest. How can we stop them? It is spoiling the plants.

Most gardeners invite and welcome birds into their gardens. Every once in a while, however, one of the little chirpers refuses to obey the local zoning ordinances and chooses to build her nest where she is not welcome. Her persistence is most amazing once her mind is made up. She will rebuild her nest nearly as fast as you can take it down. If she gets ahead of you and lays eggs, few gardeners would have the heart to disturb the soon-to-be-family.

The trick is to prevent her from getting to that point. Repellents used against rodents seldom work for birds as they do not experience taste in the same way as mammals. Physically keeping her out may be the best answer. Use a bit of tree netting over your basket (the same that is used for keeping birds off of fruit trees and berry patches). It will only have to be left in place for a couple of weeks until she builds her nest elsewhere.