When do I trim back the mums in my garden? I would like to keep them about one foot tall. How often and how much of the plant can I safely remove at one time to keep them at the desired height? After blooming in the fall, how much of the plant do I cut back? Also, when and how should I divide the plants? How many divisions can I make of one plant?

Mums planted the year before should have new tip growth pinched back every 2 to 3 weeks beginning when they are about 6 inches tall and until about the first of August. This makes them full and bushy, and loaded with blooms. It prevents the tall leggy mum that opens up in the center and flops down. Repeated trimming holds down their height.

This year, however, our hot weather has accelerated many of our plants. So if you sheared or pinched your new growth in early August, you probably sacrificed any fall blooms before the first hard frost. If you don’t have the time to trim back tip growth every 2 weeks, a rule of thumb is to trim the plant by half around Memorial Day and trim again by only a third around the Fourth of July.

In late fall, the first hard frost generally kills the vegetative growth. Once the plant is dormant, cut off the stems about 4 to 6 inches above the ground, clean up old leaves and debris, and mulch the area. In spring, when new growth appears, you can make more plants by dividing the new offsets from the original crown. You are only limited in the number of new plants by how many offsets the crown has produced. Remove them carefully with as much of their root system as possible. Transplant to your area of choice or place in pots for later planting.

I have a problem area under my maple tree (tree roots and shade). I want to plant flowering perennials with a maximum height of 6 inches that would provide blooms throughout the summer. Are there such plants?

The area under maple trees is deep shade with dry, root-filled soil and it presents a challenge, but is not impossible to garden. The trees absorb the moisture first, leaving plants underneath thirsty. The soil often lacks nutrients as the trees absorb them first as well. And, of course, there is the lack of light. Thinning the tree branches overhead allows more light to reach the ground.

Before planting anything, add copious amounts of good compost, aged manure, leaf mold and other organic matter to improve the soil structure, nutrients and water retention. Improving the soil will help the following plants do well under your maples.

You may want to consider a groundcover. This works whether you want a formal or a naturalized effect. Groundcovers tidy up the garden, hide the mulch and define the edges. Some groundcover choices are deadnettle (Lamium), pachysandra, myrtle (Vinca), and lily-of-the-valley. Lilyturf (Liriope) is a small, clumping grass-like plant that has small flowers on a central stem. There are some lovely perennials that will be happy in your location. Barrenworts (Epimedium) are known for their neat habits and undemanding requirements.

There are some nice choices for leaf and flower color as well. Sweet woodruff (Galium odoratum) is a deciduous groundcover that will quickly develop huge mats of soft green stems that smell like vanilla. Early spring bulbs, corms, and tubers like crocus, Siberian squill (Scilla), and Cyclamen coum, which will bloom and then go dormant, seem to prefer dry summer conditions. All kinds of hardy geraniums will grow well and flower throughout the summer as long as you deadhead them in mid to late summer. Pigsqueak (Bergenia cordifolia) will take fairly deep shade, producing flowers in mid-spring.

Coral bells (Heuchera) are reliable plants in the shade and new cultivars are appearing every year that have many interesting leaf colors from burgundy to silver to bronze. Their small bellflowers on wiry stems show off all summer. Heucherella is a cross between Heuchera and foam flower (Tiarella) and is also a good selection. ‘Quicksilver’ is especially nice with silvery, metallic leaves that reverse to a rich, red purple. Hostas are also appropriate and make a pleasing picture when planted with coral bells and Heucherellas. Add Japanese painted fern and you have a lovely variety of color, size and texture.

What exactly are the suckers on tomato plants? I was told that if you pinch them off, your plant will concentrate on growing the fruit, instead of producing the suckers. When should I pinch them off? How do I determine which ones they are?

Pruning directs a tomato plant’s energy from producing foliage to the production of fruit. Pruning involves removing the lateral branches—also known as suckers. Suckers arise at the junction of the leaf and the stem.

Some of the advantages of pruning are larger fruit, earlier-maturing fruit, the ability to have closer plant spacing, easier pest control, and easier harvest. The disadvantages of pruning can include fewer fruits per plant and increased labor.

The primary factor in determining how severely to prune a plant is the plant type—indeterminate or determinate. An indeterminate plant keeps growing and producing fruit until it’s killed by frost or disease. When the branches of a determinate plant reach a certain length or age, they stop growing and producing fruit. 

The indeterminate varieties are generally pruned down to one or two main stems. In the single-stem system, all of the lateral branches, or suckers, are removed. In the double-stem system, all but one of the suckers are removed. The sucker immediately below the first fruit cluster is allowed to grow and produce a second stem, which will also produce fruit. All suckers on the second stem are removed.

The suckers on determinate plants are normally removed as they would be in the double-stem system with indeterminate types. The sucker immediately below the first fruit cluster is left intact. Depending on the natural vigor of the variety, two or three suckers below this fruit cluster may be left intact.

If you are going to prune, wait until the suckers are large enough to handle easily (1 to 2 inches long). Simply pinch or snap off the suckers. Keep an eye on the lower branches of a tomato plant for further pruning. The lowest branches are prone to be the first infected by fungi or disease, as water splashed from the ground may carry spores to the lowest branches. When the branches and/or the leaves show signs of spotting or yellowing, the entire branch should be pruned and the material disposed of. Do not compost this material as the compost pile may not get hot enough to sterilize it.