How late in the season can I plant newly purchased perennials? How late can perennials be divided and transplanted?

The nice thing about nursery-grown perennials is that they are already “hardened off” when you purchase them. Perennials that have been container-grown and have gone dormant through one winter season in the pot are considered “hardened off” plants; they will be winter hardy. This makes your success rate greater when planting perennials late into the season. You can plant hardened-off plants up until the ground freezes. When planting later in the season, be sure to prepare the soil properly depending on the particular plant’s needs. Also use a root stimulator like Root ’n’ Grow to give the plant a jump start to a healthy root system.

After the foliage of the perennial dies back from frost, cut back the dead leaves to about 3 inches from the ground and cover the entire plant with a light mulch about 3 inches deep. Using pine straw mulch is recommended because it is light enough to allow air circulation at the plant’s crown in order to prevent rotting and at the same time it will insulate the root system for the winter. Winter mulching perennials is an important maintenance step every year, but it is especially important with newly planted perennials.

As general rule, perennial division can be done after the plant is finished flowering for the season. Since division greatly stresses the plant, it should be done early enough to give the plant at least one month in the growing season to reestablish its root system. Dividing on a cool day is also recommended. A first-year perennial should not be divided as it needs at least one growing season to become hardy and healthy enough to handle division.

Find more information here on dividing tulip bulbs.

I have a number of chrysanthemums which are about 1 foot tall. When is the best time to cut them back? What is the purpose of cutting them back?

You will want to cut your plants back twice during the growing season. The first cut will be early spring when the mums reach a height of 8 to 10 inches. At this time, cut about half the growth off. The second time you cut should be no later than July 1st, again cutting about half the growth off. This will not only triple the amount of flowers each plant will get, but also helps to keep the mums compact instead of tall and leggy.

What do I use to rid my yard of ground ivy and when do I apply it?

Ground ivy is a very invasive, perennial weed that is sometimes difficult to control. One of the most effective ways to rid your lawn of ground ivy is with the use of a Trimec-based herbicide. On an established lawn, the best time to apply Trimec is when the ground ivy is actively growing. For best results, apply it in the spring, when the weed is at an immature state. On a newly seeded lawn, you must wait until the lawn has been cut at least twice with a lawn mower before applying any herbicides, as damage may occur.

Trimec can be applied either in liquid or granular form. It is recommended that you avoid rain or water for at least 24 hours after application. This will allow the herbicide time to take effect. Because ground ivy is so invasive, repeat applications, according to label instructions, may be necessary. Once you have your ground ivy under control, maintaining a healthy, well-fertilized lawn will help eliminate the possibility of the problem returning.

While I am a relatively new to gardening, my garden is coming along well and I had many different flowers this season. I do, however, have a concern — how do gardeners work in flower beds with loads of bees buzzing all around them? I know the bees are beneficial, but it’s really kind of nerve-racking. Are there repellents to use that will keep them away from you? I wouldn’t say I have a fear of bees, I just don’t particularly like getting stung! Any ideas or suggestions?

Bees are beneficial, and short of turning your garden into a chemical war zone, it is really difficult to avoid luring bees into the garden. Observation will show you that they prefer certain flowers over others. If bees are truly offensive to you, you may wish to avoid planting those particular flowering plants.

Most bees, however, are not aggressive unless threatened. Avoid wild or hurried movements if a bee should approach or land on you. Simply move out of the way or lightly shoo it away. For many species of bees, stinging is a suicide reserved for protection of the hive.

I stored cannas over the winter in an aluminum tin filled with peat moss. How do I know it they survived the storage OK? What should I look for? When and how should I replant them in the garden?

Cannas are generally easy plants to carry over as long as the tubers are not allowed to freeze and they do not dry out excessively. The ideal storage temperature is in the 50 to 60 degree range. Canna tubers stored in an unheated garage will freeze and be literally mush by spring. On the other hand, cannas stored in a hot closet in a paper bag become shriveled, dehydrated lumps by spring. This does not have to be the case!

To properly store cannas:  Lift the cannas in the fall just before or right after the first light frost. Leave the tuber clumps together even if they have become large. Rinse off the excess soil from the tubers. Allow the foliage to dry, then detach the stems from the tubers. Store the tubers in sphagnum peat or vermiculite in a container that “breathes,” like a cardboard box (not plastic!). The trick here is to minimize air movement around the tuber.

If you’ve done it right, your tubers will be firm, yet plump. They should not be moldy or have a slimy coating. New shoots, or “eyes,” may be evident as tiny points on the tuber. Tubers may be divided prior to planting—maintain at least 2 to 3 eyes per piece. Dust the freshly cut pieces with micronized sulfur and allow to dry a day or two before planting to minimize the chance of rot. Plant them outside about the same time you would plant other hardy annuals—when the danger of frost is mostly gone (mid-May). To get a jump on the season, cannas can be started indoors 4 to 6 weeks ahead of the last frost date.How 

I have read articles that indicate specific soil temperatures are required before planting certain plants in the spring. How do I determine what the soil temperature is? Are there actual soil thermometers to use?

The uptake of water and nutrients is greatly affected by soil temperature. Seed germination is also affected by temperature. Planting before the soil is sufficiently warm can delay or prevent the establishment of many plants.

As you might imagine, not all plants are the same. Cool season crops like peas, cabbage, lettuce and onions can be planted and will establish when soil temperatures are still quite cool (45 degrees Fahrenheit). Tomatoes and peppers, however, will not grow well until soil temperatures reach 59 degrees or more. Melons and cucumbers need temperatures in the middle 60’s to take off. Most flower and herb seeds require a minimum temperature of 62 degrees, but will germinate faster if warmer.

Soil thermometers are available at many garden centers. Expect to pay between $10 and $20 for a good thermometer or a good deal more if you want something fancy. Insert the thermometer 4 to 6 inches in the ground for your reading. Remember that not all areas of your yard will warm up at the same time. Soil type, sun exposure and adjacent structures all influence the rate of warming. Your soil thermometer can take the guesswork out of the equation and allow you to get the earliest possible start.

I frequently read tips that recommend the ideal time to prune a plant is when it is “dormant.” How do I know when a plant has gone dormant?

Dormancy usually refers to the time that the leaves drop off and lasts until the plant leafs out in the spring. For many plants, the best time to do any major pruning would be in early spring before it starts leafing out.

Trees such as birch and maple are usually better pruned in late spring when the plant has fully leafed out. Otherwise they have a tendency to “bleed” sap at the points where they were cut. Evergreen trees are best pruned in late spring just before the “candles” of new growth harden off. As you can see, it is more important to know what kind of plant that you need to prune, and not to just prune anything just because it is dormant, because many plants will break that “rule.”

Last year, I planted healthy Purple Wave petunia plants in a container, but they hardly grew and hardly bloomed. I’ve seen great Purple Wave plants everywhere in the past. What did I do wrong last season?

Without knowing your exact environmental conditions last year, we will try to give some possible reasons things could have gone wrong. Any petunia will require at least 6 hours of sun a day. Any less than that will cause low bud counts and stringy-looking plants.

Using improper soil for a container-grown plant could be another reason. Stay away from topsoil, which is too heavy, holds too much moisture, and restricts root growth. Use a light, “soilless” mix with peat and perlite.

Fertilize every other week with a 20-20-20 fertilizer. “Wave” petunias are rapid growers and heavy feeders. Use a container large enough to let those Wave petunias grow. A pot no smaller than 12 inches would be best.

My rhododendron has a black, sooty substance on its leaves and stems. What is it and how can I correct this problem?

That black substance is probably sooty mold growing on the deposits of honeydew (excrement) left by an insect. It is often a homeowners’ first sign of trouble in the landscape. Aphids, scales, whiteflies and mealybugs produce this sugary, sticky substance. They all feed by piercing and sucking a plant’s juices. The sooty mold itself does not injure the plant. But if left untreated, it will shade the leaves, reduce growth, and invite other unwanted guests to dinner.

You can simply wipe off the sooty mold. More importantly, you need to find the source of the honeydew. Be sure to consider where your rhododendron is planted. If it is positioned as an understory feature with taller trees, your plant may not be infested itself, but merely be the honeydew recipient of an “abovestory” tree problem.

Examine your plant carefully, using a magnifying glass if necessary to identify the culprit. Aphids are a maximum of 1/8-inch long, pear-shaped, and green, pink, black, dusty gray or white fluffy-coated insects that cluster on leaves, buds, and young stems. To see if you have whiteflies, just shake a branch. The winged adults are visible and will temporarily fly away. Scales species appear as white, gray or brown bumps on the undersides of the leaves. Mealybugs are soft, oval, 1/10-inch long insects with distinctly segmented pinkish bodies.

Once you’ve identified the insect, you can select a control. Follow the control product’s directions for repeat applications. The watchwords for you are vigilance and diligence to keep the insects from making your plant a five-star restaurant!