<em><b>Josie writes:</b> I have been studying the new-growth habits of Chinese pistache trees for several years and each spring I have observed that some trees are much slower to leaf out.

My first thought was the trees that didn't exhibit the vigorous new leaf growth were troubled and would soon die. Now that it is mid-May, all the Chinese pistache trees are fully leafed-out and are obviously healthy. Can you explain why this happens each year?

By the way, all the trees are in a large parking area in a shopping center, so it is easy to make comparisons due to their proximity to each other. And, only some of trees are loaded with berries in late fall. </em>

Chinese pistache trees are diocious, meaning there are male and female trees. Both male and female growth rate is based on the species, soil and climate conditions.

However, female trees tend to be somewhat smaller and they will form and drop colorful fruits in the fall. Obviously there must be both male and female trees in the vicinity since you have observed the female trees with colorful berries in the fall.

For female trees to form fruit, they require a male tree for pollination.

A Chinese study published in 2013 found that male trees had small main branch angles and an upright tree crown with vigorous growth. Female trees had large main branch angles and an open, loose canopy.

Perhaps you are observing the early differences in leafing-out between male and female trees. It will be fun to keep a seasonal journal of their growth patterns and note their limb/canopy structure. The question is: Do male or female Chinese pistache leaf-out first?

For those readers who are interested in buying a Chinese pistache, botanically known as Pistacia chinensis, look for the fruitless male clone, "Keith Davey." It is a recommended choice for selecting a Chinese pistache tree that is to be planted by sidewalks, overhanging parking areas or in garden areas where fruit litter can be a nuisance.

Also, if there are small children in the home, take note that the female trees' berries are edible only for birds, not humans. Again, choose the male clone, "Keith Davey," a perfect specimen.

<em><b>Julie W. asks:</b> My favorite clematis, Clematis montana rubens, was chewed by our new puppy. It was necessary to prune it way back and now I wonder if there is a possibility of it blooming again this season? </em>

Sorry to disappoint you, but no, it is very unlikely since it flowers on stems produced the previous year. You should have a good show next year if you protect the new growth with some strong circular formed wire wrapped around the base of the vine. This wire also will give the clematis a nice trellis to climb on, providing you plan on accommodating its expected yearly growth of 20 feet.

Some thoughts and tips about drought-tolerant plants:

Did you know that many drought-tolerant plants share similar characteristics? Following are a few general characteristics that will help when shopping for a xeroscape garden, even if you are not immediately familiar with plant names. Then continue to refine your plant research beforefinal plant purchases.

Large leaf size usually indicates higher water needs, so look for plants with smaller leaves.

Grayish, fuzzy leaves adapt and survive dry conditions.

Low-growing plants hug the ground and survive hot, drying winds.

Leaves on plants that are divided into smaller leaflets are survivors.

<em><b>Sally F. asks:</b> I have tried many times to grow lavender and each year they die on me. What kind of soil do they like to grow in? I have a clay-type soil.</em>

The most important thing to remember about lavender is that all lavender plants are native to the Mediterranean and, therefore, prefer a loose, fast-draining soil and hot sunny weather. They require at least six hours of direct sunlight to produce blooms. Plants growing in filtered sun will produce few blooms. It is best to water the plants at their base with a drip system that will eliminate overhead watering. Soil should be almost dry between watering. Applying mulch away from the base of the lavender will help conserve water. Incorporating some compost into the soil in the planting area will help with poor drainage.

<em>Send your gardening questions to The Garden Doctors at pdgardendoctor@gmail.com. The Garden Doctors, gardening consultants Gwen Kilchherr and Dana Lozano, can answer questions only through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.</em>