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As an avid plant person who is also a metalsmith and jeweler, I was surprised to learn that we get the weight measure for stones (carat) from the ancients who used carob beans as a standard weight. Because "carob beans are unusually consistent in size. This means that carob beans usually all weigh the same, no matter when or where harvested!"

My mind is reeling! How can that be? Nature doesn't do that! Every plant is unique, I thought, weather, soil, location should change the harvest, I thought. Am I mistaken?


On that last point, you are not mistaken: there is variability in the weight of carob seeds, but it is relatively small. Ceratonia siliqua is in the bean/legume family [Fabaceae]. It is not the elongated carob pod that was used as a standard, it's the seeds contained in that pod ( a typical pod contains about 10 seeds). Seeds from female trees are relatively consistent (0.197 grams or 1/150th of an ounce). This weight was standardized to 200 milligrams in 1907, and continues to be in use.

The scientific paper Seed size variability: from carob to carats (Turnbull et al., 2006, Biology Letters: The Royal Society, published online 2006 May 2) attempts to explain the "myth of constant seed weight." As far back as ancient Greece, there was a weight called a kerat (which is echoed in carob's Latin genus name, Ceratonia). Keration was the Greek word for carob (possibly a Semitic loan word from Aramaic/Syriac karta meaning pod or husk), and its literal meaning was 'little horn,' which describes the shape of the pods (not the seeds). Siliqua, carob's species name, was the Latin word for carob, and used to refer to the smallest subdivision of the Roman pound. Carob seeds were no more consistent in mass than the other 63 species the article's authors measured. They theorize that seeds used for weighing were a product of human selection.

Carob thrives in its native Mediterranean and Middle Eastern regions, and would simply have been readily available as a counterweight for precious substances, like gemstones and spices. Humans can perceive mere 5% differences in carob seed mass. In the ancient world, measurement of weight based on carob seeds would have been fairly dependable, based on the accuracy of the human eye—unless an unscrupulous vendor also kept sets of seeds that were heavier or lighter than the standard, either to shortchange or overcharge!


What is the botanical name for water chestnut? Will it grow here? Are there other water plants that have edible tubers which will thrive in the Pacific Northwest? What about edible lotus root, from Chinese lotus?


Chinese or Sacred lotus (Nelumbo nucifera) is hardy in zones 4-10 and is considered invasive in some parts of parts of the midwestern and southeastern U.S. This article in The Guardian by Mark Griffiths, author of The Lotus Quest, suggests growing it in a container in a conservatory or on a sunny deck. However, you may not want to harvest tubers from a lotus grown in a relatively small container, as the plant needs to be large enough to have a substantial system of linear growth in order to sacrifice some of its tubers for human consumption. According to the Colorado Water Garden Society, "Lotus grow in a linear fashion, with a sequence of a tuber producing a leaf and perhaps a flower, then beginning another tuber to repeat the cycle . . . Tuber, leaf, flower, tuber, leaf, flower, etc. Each terminal point produces a single leaf and flower and then sends out the next, new growth. Beneath the soil, lotus growth takes on one of two forms: runners and tubers. The Summer "runner" growth is thin and long (to 24"+)."

American yellow lotus (Nelumbo lutea) also has edible tubers, but it can be an aggressive grower. If you are seeking out plants, be aware that there is sometimes identity confusion among Nelumbo, Nymphaea, Nymphoides, and Nuphar. In King County, there are two common invasive water lilies that are sometimes mistaken for lotuses, Nymphaea odorata and Nymphoides peltata. While some of these water lilies have tubers that have been considered edible in times of famine, they are not a desirable food source.

The common name 'water chestnut' may refer to the edible corms of the Chinese water chestnut familiar from Asian cuisine (Eleocharis dulcis), which is in the sedge family (Cyperaceae), or to European water chestnut (Trapa natans), which is in the loosestrife family (Lythraceae). Eleocharis is not winter-hardy in our area (it requires zones 9-11). Trapa natans is a noxious weed in Oregon and is on the Washington State Noxious Weed quarantine list, so it is not a good choice if you are planning to grow your own aquatic plants. Green Deane's Eat the Weeds webpage describes the differences between these plants.

One commonly grown native plant with edible tubers is Sagittaria latifolia (common arrowhead, wapato, duck potato). It is an attractive ornamental in a water garden. According to Missouri Botanical Garden, the starchy golf-ball sized tubers that develop at the ends of the rhizomes (underground runners) "are edible, and may be boiled or baked and eaten as a potato-like food. Native Americans harvested and consumed these tubers, which in some areas were known as wapato. The tubers are also an important food source for waterfowl, hence the name duck potato." According to Eat the Weeds, only Sagittaria latifolia is of edible interest to humans because the size of the tubers or corms is more significant than in other species. Generally, the larger the leaf size, the larger the edible tuber. In any case, avoid planting the two species of Sagittaria on the Washington State Noxious Weed list: S. platyphylla (quarantine list) and S. graminea (class B).


What's an Amarine and should I grow it? Also, when do you plant the bulbs?


x Amarine is a cross of the South African bulb Nerine and Amaryllis belladonna (Naked Ladies). According to the Pacific Bulb Society, the plants have larger flowers than Nerine. The cross was developed in the Netherlands in 1940, according to this article by Graham Duncan of Kirstenbosch National Botanical Garden in South Africa.

This British commercial gardening site says that x Amarine improves upon Nerine's reluctant and unpredictable blooming habits. x Amarine keeps its foliage while it is blooming. Nerine, on the other hand, produces foliage in the spring and flowers when the foliage dies back in autumn.

In his article on Belles of the Autumn Border, Graham Rice says that × Amarine tubergenii is in between its parents in flower numbers and flower size. For a Pacific Northwest perspective on growing Nerine (and its cousins), you may find Susan Calhoun's article in Fine Gardening useful. As far as when to plant these fall-flowering bulbs in the Northwest, we suggest doing it in May when all danger of frost is long past.


I noticed a Seattle P-Patch garden that was using milfoil from Lake Washington as a mulch in the vegetable beds. That made me wonder about using other aquatic plants as mulch, such as seaweed. Would this be beneficial to the plants? Or would it add salt to the soil and cause problems?


Milfoil (Eurasian watermilfoil, or Myriophyllum spicatum) is a Class B noxious weed in Washington State, and it is on the quarantine list. I am not sure whether moving milfoil dredged from the lake into a garden as mulch violates the quarantine’s prohibition on 'transport of plants,' but presumably it had died back before being spread on the beds. When the plants decay, they do impart nutrients (potentially beneficial to the soil, but a detriment to the lake because they cause algae growth), but Lake Washington is not a pristine body of water, and I would be somewhat concerned about pollutants.

As for using seaweed as mulch in the garden, the book Seaweeds: Edible, Available & Sustainable by Ole Mouritsen (University of Chicago Press, 2013) notes that seaweed has been used as fertilizer for centuries in coastal regions. "In France and on Iceland, this practice goes back at least as far as the 14th century." In Scotland and Ireland particularly, scraps of seaweed that wash ashore have been added to soil to form raised beds for potatoes and other crops. Such beds hold moisture well, but there is a concern about soil salinity (harmful to earthworms and some plants) and pollutants from contaminated water, so it is best to wash the seaweed in rainwater before use. Plants that were originally shore plants, like asparagus, cabbage, and celery are more salt-tolerant.

There is an enlightening discussion on the University of British Columbia Botanical Garden forum about using seaweed in the garden. A biologist urges rinsing the seaweed at the beach to free any creatures that might be attached to it. Even desiccated seaweed higher up on the beach harbors living things that will not survive if you unwittingly transport them with the plants you are collecting. Additionally, there may be seeds and roots of other plants you might not want to introduce into your garden.

It Is worth noting that you must have a license to harvest seaweed from Washington beaches; it is not permitted everywhere, and where it is allowed there is a ten-pound wet-weight limit. There are specific guidelines on what tools to use, and how to leave behind the base of the plant so it can continue to flourish. Be mindful that seaweed is an integral part of a complex ecosystem, and you do not want to disrupt habitat and food sources when gathering plants to use as mulch. Also heed any notices posted about pollutants that may have been released in the water where you are harvesting.

All of this being said, it does not make much sense to collect seaweed for mulch unless it is 'in your own backyard,' that is to say, you live near the beach. There are more sustainable mulch options (feed a compost pile with materials already in your garden, and use that as mulch; obtain free wood chips from a local arborist) that do not come with so many environmental factors to consider.


Where can I get information about garden designers? I am more interested in designers than landscape architects.


Some sources of information and contacts for garden design are

Plant Amnesty's Referral Service

Association of Professional Landscape Designers (look for APLD Chapters and then choose from the list of states/regions)

Edmonds Community College graduates in Horticulture are sometimes featured on the program's Home page when they start businesses. You might also contact the department and see if they have information about garden designers.