Gardening Answers Knowledgebase

Question:

Each year, in early autumn, I notice tree leaf silhouettes staining the sidewalk. Do all trees do this? I mainly see maples and occasionally oak leaf shapes. What substance in the leaves causes this staining effect?

Answer:

Tannin in the leaves is responsible for leaving behind those silhouettes. Rain rinses the tannins from the fallen foliage, and leaves a trace. The prints are most visible on lighter colored surfaces. This is similar to the way strong black tea leaves a tannin stain on porcelain cups and tooth enamel.

The very word 'tannin' has its origins in the Latin, tannum, meaning the bark of an oak tree (which was used to tan animal hides to make leather). Oak has especially high levels of tannins, but because its leaves are thick and take longer to decompose, you may notice fewer leaf prints from oak trees.

Tannins are widespread in many different plants, and may be present in many parts of a plant. They are especially common in leaf tissues, "particularly in the cells of the upper epidermis (on the top surface of a leaf)."

The substance may also be found in the bark and wood of trees, as well as the buds, stems, fruits, seeds, roots, and plant galls, where it may provide protection to the plant. For example, cottonwood trees can adjust their level of tannins to defend against beavers harvesting their wood.

Question:

I am researching the early years of the Washington Park Arboretum for a historical narrative I'm writing. Can you tell me what is growing near the footbridge from E. Lynn Street into the Arboretum in a January 1912 photograph? Do you know when the bridge was constructed?

I did find a 1935 plan from the Olmsted archives which seems to have a full inventory of plants, but some of the abbreviations escape me.

I am seeking any other online sources that might help in my research.

Answer:

The bridge, designed by the architects William Sayward and Walter Willcox, was built in 1910, and at the time was referred to as the Arboretum Sewer Trestle or the Arboretum Aqueduct. Because the photo was taken in winter, it does not provide useful clues about the bare shrubs and trees. However, the 1935 plan does yield information, assuming some of those plants would have been there at the time of your photo. I can decode some of the abbreviations (such as Syc for sycamore, V.M. for vine maple, and Cot for cottonwood, W for willow, and A could be alder), and an awful lot of “Cat,” which turns out to be Catalpa, according to the 1936 plan's Legend of Trees in the high resolution version of the image.

In addition to the Olmsted archives online, you may find these links useful:

• Washington Park Arboretum Historic Review
• Seattle Municipal Archives Digital Collections, searchable by keyword
• Museum of History and Industry (search digital collections)
• UW Libraries Digital Collections
• About the Arboretum Sewer Trestle
• Paul Dorpat's Then and Now, on the Willcox Bridge
• National Register of Historic Places application: Lake Washington Boulevard history—see section 2 on the Arboretum and the footbridge: excerpt:
  "A significant feature of the Washington Park Arboretum that passes directly over Lake Washington Blvd. near the arboretum’s northern extent is the Arboretum Aqueduct and Sewer Trestle (also known as the Willcox Footbridge) (Contributing Resource No. 2; 1910). The bridge is a multiarched, concrete-and-brick pedestrian bridge that filters foot traffic over Lake Washington Blvd. The City built the structure in 1910 to carry a newly constructed sewer line over low ground. The aqueduct is a Seattle City Landmark and was listed in the NRHP in 1982."

Click the image to view close-up.

Question:

While taking a walk in the neighborhood, a weedy-looking plant caught my eye. It had nubbly, deep red fruit all along the stems and was quite dramatic by contrast with the tattered-looking leaves. The gardener said it was leafy goosefoot. What can you tell me about it?

Answer:

Leafy goosefoot refers to Chenopodium foliosum (or its synonym Blitum virgatum, as well as a related species, Blitum capitatum). Another common name is 'strawberry blite,' not to be confused with blight of any kind, but derived from the genus name Blitum. The leaves do resemble the footprint of a goose. Those nubbly strawberry-like fruits that are produced from summer to early autumn are edible, with a mildly sweet flavor or--according to a 1794 issue of Curtis's Botanical Magazine--"in their taste they have nothing to recommend them, though not pleasant they are harmless." The leaves are also edible and similar in both appearance and flavor to spinach, which is why another name for the plant is 'strawberry spinach.' It has value as a beneficial plant for wildlife, and it has a history of being used to make dye and ink.

Strawberry blite is a wild and weedy plant that can tolerate harsh conditions, as demonstrated by its ability to grow in landscapes ravaged by wildfire.

Question:

What are LECA balls, and should I use them for growing my indoor plants? I have been seeing them for sale at garden centers.

Answer:

LECA stands for 'lightweight expanded clay aggregate,' and is made from clay, brick dust, and waste from the processing of albite (a sodium-rich mineral derived from feldspar). The primary use of the clay balls is as a substrate in hydroponic growing. A similar product is sold under the brand name Hydroton. From the point of view of hydroponics, LECA may be beneficial because the spaces between the clay balls offer more airflow and ease of root development, but the LECA balls have "limited water holding capacity (only a problem if you forget to water or let the water level drop)." Their absorption rate varies based on the make-up of the aggregate; the more pulverized brick and albite, the less they absorb.

Houseplant enthusiasts may mistakenly assume that using LECA balls will free them from being attentive to watering and drainage concerns. Some promoters of the clay balls suggest that you can soak them and grow your indoor plants in a container without drainage holes because the balls somehow magically provide the roots with just the right amount of moisture. It may be a stylish (if expensive) look, but it is still best to grow your indoor plants in the appropriate potting soil for their needs, and in containers with drainage. Definitely do not mix clay balls with potting soil, and do not use them in the bottom of containers. The myth of improving drainage by putting various items in the bottom of a pot (whether an indoor or outdoor container) has been debunked. Don't create a perched water table by putting anything—clay balls, broken pottery, rocks, etc.—in the bottom of the pot. When we do this, "water percolates through the soil and, upon encountering the different layer, the water moves sideways, creating a saturated zone. Water in this saturated zone gets 'hung up' [or 'perched'] on the layer that is different.”

Question:

Our stand of black bamboo that has flowered is dying back. It was already escaping its barrier, but now I am concerned about the flowers producing seed that take hold everywhere. When we cut it down, should we be careful about not letting seeds scatter? I've heard that when one bamboo flowers, it coincides with other bamboos flowering. Is there going to be a massive die-off of bamboo?

Answer:

You can certainly lay out a tarp for your cut bamboo, its flowers, and any potential seeds. If you are curious about seed viability, you can put some in containers and wait to see if they germinate. Some bamboo species have larger seeds that are easier to see, while others are small and easily obscured by decaying flower parts. Seeds collected before they are mature are unlikely to germinate. Based on all of these details, I don't think your Phyllostachys nigra will be sowing itself all over the garden or the compost pile.

According to The Gardener's Guide to Growing Temperate Bamboos (Michael Bell, Timber Press, 2000), flowering may be partial or complete. With partial flowering (which sometimes precedes full flowering), some culms will keep on going and not die. "When a bamboo flowers completely, most of the leaves are replaced by flowers, transpiration is largely interrupted, and this triggers natural responses that hasten the aging of the culm," eventually resulting in eventual death.

Depending on the species of bamboo, flowering is a fairly infrequent occurrence, and there are multiple theories about what prompts it. It can happen once every 30-60 years up to intervals of over 120 years. (There are just a few unusual species that flower yearly.) Bell says anecdotal accounts suggest that bamboos rarely if ever set seeds but, in his experience, "it is very rare that bamboos flowering in earnest do not set some seed during one of the years of their flowering cycle." Clumping (sympodial) bamboo species will flower in winter and produce seed in spring, while running (monopodial) species like your black bamboo will flower in summer and produce seed in fall.

You mention the phenomenon of many bamboos flowering in unison. This is sometimes called mass synchronous flowering, or gregarious flowering, and can occur across the globe. According to Bamboo by Robert Austin and Koichiro Ueda (Weatherhill, 1970), "practically every bamboo of the same species, young or old and however widely separated they may be […] will flower in or about the same year." Flowering in bamboo is complex and incompletely understood. A more recent scientific article, "The Bamboo Flowering Cycle Sheds Light on Flowering Diversity" by Xiao Zheng et al., classifies flowering into four categories: sporadic, massive synchronized, combined massive synchronized and sporadic, and partial flowering. Depending on the species of bamboo, regeneration can occur through sexual reproduction (seeds) or asexual reproduction (rhizomes forming small, weak shoots at first, as "the proportion of flowering bamboo generally first rises and then falls, while the proportion of non-flowering bamboo falls and then rises." If your black bamboo dies, it is still possible you may observe some regeneration that follows this pattern.