Ask Mr. Smarty Plants

We very recently answered a similar question, having to do with roots getting into the lateral lines from a septic tank. You really have to consider the whole system when planting over it, because of the damage roots can cause. The tank should be sealed to prevent roots invading it, but you don't want to take any chances. Our Native Plant Database agrees with you on the problems with Juglans nigra (black walnut), saying, in part: "Nuts may become a nuisance as they litter and stain. Foliage is often attacked by caterpillars, and the species is susceptible to anthracnose which defoliates trees for the season."

You don't want any woody plants close to your lateral lines, as in trees and shrubs. They are the ones that send roots out far beyond their driplines, sneaking up on you. But you don't want to leave that area completely bare, because you know it wouldn't stay bare, it would get weedy and unless it was mowed, some of those "weeds" would grow up to be woody plants. We don't know how your lateral lines are situated, but you do need to be aware of them as you plant a replacement for your walnut. If the area is too near the lateral lines, you may have to reconsider what you plant there. 

We located a website that made specific recommendations on what should be planted above lateral lines-grass! The Ford County Kansas Septic System Information site gives a lot of good information on how to manage a septic system, but the piece of information we were most interested in was that perennial short grasses should be planted above the lines. Apparently, the shorter the grass, the shallower the roots. Furthermore, the grasses will assist in evaporation from those lines, and should thrive with that unaccustomed dose of moisture. We could find no specific information on Berks County, nor any advisories concerning septic systems there. So, we're going to assume that the use of native grasses over the entire system is the safest, most economical way to maintain that system.

If you have determined that roots from a woody plant will not be a threat to any part of your system, we will go to Recommended Species, click on Pennsylvania, and search on "trees" for habit. Then, we will take a look at the webpage for each plant and see what height it will reach, etc. We will also search on "shrub" because many trees will grow beyond your height specifications, but some shrubs can come near to the height you are contemplating. When we did this, we discovered Pennsylvania has lots of BIG trees and no native shrubs that come anywhere close to your requested height. So, we chose six trees to recommend; none of which fill all your specifications completely, but come close. These are all commercially available; you can find Native Plant Suppliers by going to that site and typing your town and state in the "Enter Search Location" box.

SMALL TREES FOR PENNSYLVANIA

Betula populifolia (gray birch)

Juniperus virginiana (eastern redcedar)

Nyssa sylvatica (blackgum)

Ostrya virginiana (hophornbeam)

Populus tremuloides (quaking aspen)

Prunus americana (American plum)

Betula populifolia

Juniperus virginiana

Nyssa sylvatica

Ostrya virginiana

Populus tremuloides

Prunus americana