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LECA balls

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


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.”

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The Inspired House Plant

Jen Stearns is the owner of Urban Sprouts, a houseplant specialty nursery in Renton, WA.  Her new book, “The Inspired House Plant,” aims to make your indoor space more festive by promoting a great diversity of indoor plants and teaching you to be a good plant parent.  The emphasis is on foliage – so no African violets or orchids, but that doesn’t mean the selections are dull.

Successful display is critical for enjoyment and various options are considered, including bowls, terrariums, and plants in containers of water – fish are optional.  Vertical and hanging plants are encouraged and one chapter is devoted to using your plants to enhance your overall interior style.  Of course, there is some promotion of the author’s business, but the cultural advice is sound and this nicely designed book will encourage your creativity.


Excerpted from the Fall 2020 issue of the Arboretum Bulletin


Growing ginger in Seattle

Can I grow ginger here in Seattle?

Culinary ginger, Zingiber officinale, can be grown in a container. As long as you are not hoping to grow it outdoors year-round or to harvest ginger root, you should have good success. A webpage (no longer available) from the National Botanic Garden of Wales has useful instructions on doing this:

“Look for a ginger root with green, bumpy buds. Half bury the root in compost. A mushroom container makes an excellent pot. Put the pot in a warm, sunny place indoors. Keep the compost damp. When the buds start to shoot keep the plant in a warm light place, but not in full sun. A north facing window is good.

Keep the plant warm and watered in spring and summer. In the autumn it will die down, so keep the compost dry until it starts to grow again in spring. It may need watering in spring to start it shooting again. If you are lucky it may flower in July in the second year! The flower spike is worth waiting for. A healthy ginger will grow to a height of 1 metre (3 feet).”

Sunset Western Garden Book (2007) lists this plant as a perennial but not an outdoor plant in the Pacific Northwest. (Ginger grows in tropical areas, and is commercially grown in the U.S. in Hawaii.) They recommend buying fresh roots at the grocery store in early spring. Cut the rhizomes into 1 to 2 inch-long sections, making sure each has well-developed growth buds. Let the cut ends dry, and then plant just below the surface of rich, moist soil. Water with caution until top and root growth begin. Feed once a month. Plants are dormant in winter. If you are growing them to harvest the rhizomes, this can be done at any time of year, but it will take several months for them to attain any size.

growing herbs indoors

I want to grow herbs indoors, especially over the fall and winter. Can you recommend some good books, and tell me how to get started? What’s the minimum temperature for growing them?


One of my favorite general books on growing herbs is by a Seattle gardener and author, Mary Preus, entitled The Northwest Herb Lover’s Handbook (Sasquatch Books, 2000), but there is limited information on growing them indoors. Another book, The Edible Indoor Garden by Peggy Hardigree (St. Martin’s Press, 1980) includes a section on herbs to grow as well. Most of the herb gardening books discuss bringing culinary herbs which have been growing outdoors inside during winter, when it is less possible to grow them outdoors. According to Patrick Lima, author of Herbs: The Complete Gardener’s Guide (Firefly Books, 2001), “a thriving indoor herb garden depends on good sunlight–a sun room, greenhouse or large south-facing window–but many herbs need winter rest. Obvious choices for wintering indoors are tropical herbs or Mediterranean plants–fruit and pineapple sage, scented geranium, rosemary, bay…” The best choices for fresh winter use are basil, parsley, tarragon, oregano, the mints and hardy savories, chives and garlic chives, rosemary, tropical sages, lemon verbena, and scented geranium.

The National Gardening Association has useful information on indoor herb gardens. Here is another article from the same site.
This gardening blog focuses on using recycled containers, such as growing herbs in old dresser drawers (but make sure not to use furniture that may have been painted with lead-based paint!).

This University of Missouri Extension link (now archived) has a useful guide to indoor herb gardening, excerpted below:
“Growing herbs indoors by Kathryn Keeley,MS,Former Horticulture Specialist

In 1652, Nicholas Culpeper wrote The English Physician, which combined the folklore and traditional medicine that surrounded herbal usage during that time. Colonists in North America consulted this book as a medical reference. Herbs served a variety of functions in the pioneer home, including curing illness and disease, dyeing fabric and repelling insects.

Today, consumers are turning to herbs for increased health and vitality, as well as for more domesticated duties such as decorating and cooking. A perfect way to get the taste of summer is by growing herbs indoors during the cold months. Here are a few tips if you’d like to grow your own herb supply:

  • Light source. Perhaps the greatest challenge when growing herbs indoors is providing them with sufficient sunlight. Herbs do best when grown in a very sunny window that receives between six and eight hours of direct sunlight each day (typically a southern or southwestern exposure). When growing herbs under natural light, be certain to rotate the pot every three to four days to ensure uniform growth of the plant.
  • If your most convenient window location does not have enough sunlight you can supplement natural lighting with fluorescent light. In general, for every hour of required sunlight expose the plants to two hours of fluorescent light. Herbs grown entirely under fluorescent lights will require between 14 to 16 hours of artificial lighting. Place herb plants no closer than five or six inches and no farther than 15 inches from the light source.
  • Drainage. Herbs demand good drainage for healthy growth. A potting mix of equal parts sand, commercial potting mix, peat moss and perlite will provide an excellent medium for growing herbs indoors. When potting your herbs, choose clay pots. They are more porous than plastic pots, allowing for better soil drainage.
  • Temperature. Be certain not to locate your indoor herb garden near a heat source, such as a radiator or heat vent. Herbs prefer temperatures below 70 degrees. If the air is dry in your home, place the herb pots in a tray of stones and keep the tray filled with water just up to the bottom of the pot. Providing ample humidity will promote good herbal growth while keeping the foliage succulent and tasty.
  • Fertilizer. When grown in containers, most herbs will benefit from occasional feeding with a liquid fertilizer, such as fish emulsion, seaweed or a general-purpose, water-soluble fertilizer. In general, feed herbs every two weeks according to the manufacturer’s instructions. Be certain not to overfeed your herbs. Too much fertilizer is far more likely to damage your herbs than too little.
  • Herb types and use. Chives, Thyme, Basil, Parsley, Rosemary, Sage, Oregano and Mints all do well indoors. Use them regularly to keep them trimmed back and prevent flowering, which will reduce the plant’s longevity.

growing and caring for citrus indoors

I have a Eustis limequat, and it’s producing flowers. Should I be taking a brush and dusting pollen from one bloom to the other? Also, I’m growing it inside. Do I need any additional lighting? I have fluorescent lights as well as full-spectrum UVA/UVB lights that I can use. Someone told me I’d need to get really pricy calcium lights, or something similar.


All the resources I’ve found suggest that citrus flowers are self-pollinating with a very few exceptions. However, your limequat (x Citrofortunella floridana) is growing indoors, so pollination assistance from you will help. Alabama Cooperative Extension, in a publication no longer available online, describes citrus as generally self-fruitful.

“With the exception of Clementine tangerine and certain tangerine hybrids such as Orlando tangelo, citrus trees are self-fruitful and do not require cross-pollination. Thus, self-fruitful types of citrus can be grown as single trees. Cross-pollination requires that two or more varieties bloom at the same time. Some varieties will not cross-pollinate each other. Satsuma and navel do not produce viable pollen and thus cannot be used for that purpose.”

I looked at several of our books on growing citrus to see if they mentioned any special lighting needs, and Success with Citrus Fruits by Sigrid Hansen-Catania (Merehurst, 1998) simply says that your artificial light source needs to provide 12 hours of light a day, if you do not have a position for the plant near a sunny window. She mentions “specially adapted fluorescent tubes which you can fix to the ceiling about 8-16 inches above the plants,” though she mentions it in the context of providing adequate light during winter months.

University of Missouri Extension has a general article on indoor lighting for plants.

Here is an excerpt from an article (no longer available) from Purdue University Horticulture specific to citrus: “Citrus foliage can adapt to the relatively low light levels typical of our homes. However, if flowers and fruit are what you’re after, you’ll need to give the plants as much light as possible. If natural light is inadequate, you can supplement with artificial lights. A combination of cool white and warm white florescent lights placed close to the plants will help, as will the special ‘grow lights’ that emit the wavelengths of light most important for plant growth. (…)

If citrus is kept indoors year-round, the plants will likely need a bit of pollination assistance when they do flower. Use an artist’s paintbrush or cotton swab to transfer pollen from one flower to another.”

The good news is that I don’t think you need to invest in any additional expensive lighting systems!

controlling whiteflies and recycling grass clippings

I have whiteflies on my orchid Christmas Cactus. How can I get rid of them? I also would like to know if grass clippings are good to fertilize raspberries.

Christmas cactus, or Schlumbergera bridgesii, does occasionally have problems with insects. Whitefly nymphs and adults cause damage by sucking plant juices, and their feeding can weaken a plant. They also secrete a sticky substance called honeydew, which may then harbor sooty mold. For indoor plants affected by this insect, you might try gently washing the leaves. Rodale’s Encyclopedia of Indoor Gardening, edited by Anne Halpin (1980) says that adults are easy to wipe up when it is colder indoors, and the young are usually on the undersides of leaves and may be wiped off with a sponge. Many whiteflies are now resistant to insecticides, and so it is best to start with plain water or soap and water. The book Indoor Gardening the Organic Way by Julie Bawden-Davis (Taylor, 2006) lists sticky traps, insecticidal soap, alcohol spray, oils, and pyrethrin as potential controls. There are products containing Neem oil which could help, if plain water or soapy water don’t control the problem.
Clemson University Extension has some helpful information on general care of this plant.

As for using grass clippings as fertilizer, as long as the grass was not treated with weed-and-feed or other pesticides, it should be a good source of nutrients. Also, avoid using grass which has already gone to seed. Mulch It! by Stu Campbell (Storey Books, 2001) advises not to spread the clippings too thickly, and to let them dry out a bit before using. Here is a link to Virginia Cooperative Extension’s page on recycling grass clippings.

Taylor’s Guide to Fruits and Berries edited by Roger Holmes (Taylor, 1996) says that “reasonably good soil enriched with an inch or two of good compost or a moderate dose of balanced fertilizer each year should provide sufficient nutrients for your plants to thrive. Berry lovers sometimes provide regular doses of foliar fertilizers to give their plants a boost. Absorbed by the leaves in liquid form, seaweed, fish emulsion, and similar organic materials in balanced formulations provide a broad spectrum of nutrients.”

cyclamen species and their care

I brought home a cyclamen at the beginning of November (a couple of weeks ago) and it is now the saddest thing ever. All of the leaves and flowers shriveled up and went mushy. I just cut it back to the bulb-base. I bought it from a greenhouse and wanted to keep it as a house plant. It did receive filtered sunlight. Can it come back? What should I do for it to succeed and be healthy?

If you are growing the less hardy cyclamen which overwinters as an indoor plant (Cyclamen persicum) and flowers from midwinter to spring, the following information from local gardening expert Ed Hume (now archived) describes ideal conditions for growing this plant indoors:

“In a protected spot this species will tolerate temperatures to about 25 degrees outdoors. Colder temperatures and the plants must be kept indoors. Indoors they must have ample humidity. One suitable way of providing the humidity is to simply place a glass or decorative vase full of water near the plant. Then, as the water evaporates it provides the humidity the cyclamen needs. The second most important requirement of indoor Cyclamen is the need for cool temperatures. Keep them in a room where temperatures range between 55 and 65 degrees. Keep the soil a little on the moist side, but never continually wet. Water with room temperature water. When given proper care it is not unusual for this plant to continue to grow and flower for several years.”

Is it possible your plant is mushy because of too much water? Is the indoor air too hot and dry? Here is additional information about indoor or florist’s cyclamen from University of Minnesota Extension (no longer available online):

“A cyclamen won’t be too happy in a house heated much above 70 degrees F, with the dry atmosphere that goes with it. If you are unable to provide cool enough conditions, the plant will survive for a time, but eventually it will develop yellow foliage and its blooming time may be cut short. It will probably tolerate a less than ideal location for a day or two as long as you return it to a better place shortly afterwards. The plant will tolerate indoor conditions even better if you move it to a cool spot at night. Make sure to provide as much light as possible in its daytime location.

Watering incorrectly can cause many problems, especially when too much water has been applied. Always wait until the soil surface feels dry before you water, but don’t wait until the plant becomes limp. Do not water the center of the plant or the tuber may rot. A cyclamen prefers to receive a good soaking, then dry out partially before receiving a good soaking again. Allow the plant to drain over a sink or empty the water collection tray beneath the container after a few minutes. This will help prevent the roots from remaining too wet, which can lead to rotting.”

University of California, Davis’s page on Cyclamen describes diseases and pests that may affect the plants.

It is also possible you bought a summer to fall-blooming cyclamen species which one normally grows outdoors, and it may be trying to enter dormancy. Do you have information about the species you are growing? Once we know the species name, it should help us figure out what is happening with your Cyclamen.

Growing avocado plant indoors

We have a large avocado plant (indoors) that is mystifying us. A couple months ago, it shed most of its leaves. The leaf would get droopy and the tips of the leaves would turn brown and dry out and then spread up the leaf. It got down to its last seven leaves and then seemed to stop, although all of these leaves have varying degrees of this leaf tip burn. Now over the last month or more, small new growth is appearing. They have not grown much at all and are only about an eighth of an inch long.

When growing an avocado (Persea species) indoors, you will need to be sure it is getting enough light. It is normal for the plant to drop older leaves. You should also keep the plant in a cool spot. According to The Houseplant Expert by D. G. Hessayon (Expert Books, 2001), your plant will do best if you repot it annually and pinch the tips to encourage bushy growth. Lee Reich discusses growing avocados indoors in an article (now archived) for California Rare Fruit Growers. Here is an excerpt:

“Indoors, avocado plants are often gangly and sparse with leaves. One reason for the plant’s gawky appearance indoors is light. Lack of sufficient light causes stems to stretch for it. Another reason is that avocados shed many buds along their stems, buds that might have grown into side branches. The result is a plant stretching out for light, sending out new growth mostly from the tips of the branches and shedding old leaves.

There are several things indoor gardeners can do to keep their plants more attractive. Most obvious is to give an avocado tree bright light. Also, the stretch for light is exaggerated when warmth stimulates growth, so the ideal spot for the plant is at the brightest window in the coolest room. Beyond that pruning back a stem or pinching out its growing tip stimulates branching by awaking dormant buds (not all are shed) further down the stem. There is nothing that can be done about the shedding of older leaves.”

Grown outdoors in an agricultural setting, avocado plants sometimes get leaf tip burn from salt accumulation, as this article from California Rare Fruit Growers explains. If you are using especially salty tap water or overfertilizing your plant, that might be causing the burnt leaf tips. Other causes could be lack of water, too frequent light watering, or poorly draining soil.

on Marimo or lake ball

I saw some moss balls for sale in the gift shop of the new Nordic Museum. What type of moss is used? Is it native to Nordic countries? How do I care for one indoors?


The “moss” is actually a type of freshwater alga, Aegagropila linnaei, found in only a small number of northern hemisphere lakes. Other common names are lake ball or Cladophora ball. In Japan, they are called marimo (meaning a bouncy ball that is in water). The Ainu people of Hokkaido hold an annual Marimo Festival at Lake Akan to celebrate these charming lake goblins.

Iceland’s Lake Mývatn once had the world’s largest colony of lake balls but pollution has been altering the ecosystem there, and the mats of algae balls (colloquially called round sh*t or muck balls by the fishing community) began dying out. Their disappearance was first noted in 2013. There are some recent signs that the nutrient imbalance of the lake (caused by fertilizer runoff, and accumulation of bacteria) is correcting itself and that the ecosystem of the lake is bouncing back to better health.

To grow marimo inside, you will need a container that holds water, and a spot where the algae receive indirect sunlight. They prefer cool locations in nature, so they will do best if they do not get too hot (don’t put them near a heat source, and if it gets hot in your home, you can cool them off in water in the refrigerator). To keep the balls floating, squeeze out some of the water from time to time. To propagate the algae, use scissors to divide the marimo in half after squeezing out some of the water (you can repeat this process and cut into fourths or eighths). Use thread to wrap the cut algae back into a rounded shape, tie the thread close to the ball, and put back into the water. Some people combine them with other plants and tiny shrimp in indoor aquascapes.


Garden Tip #68

Seed racks are sprouting up at nurseries and grocery stores across the city – it’s time to start seeds. One reason to start your own transplants is to save money. One packet of 50 marigold seeds typically costs the same as one 4″ little start. The budget growing may extend into seed growing supplies by using recycled plastic pots from last season or even reusing individual yogurt containers or other comparable containers. “Growing chambers” can be made on the cheap from clear plastic bags and chop sticks to keep the moist plastic off emerging sprouts. The frugal gardener will be tempted to put those seedlings in a south facing window, but beware: Pacific Northwest windows are NOT bright enough to produce healthy, sturdy seedlings.

Invest in a 4 foot fluorescent shop light from the hardware store. It is worth the small amount of money. Buy one 40 watt cool tube and one warm tube, or if you’re feeling extravagant buy the full spectrum grow lights, which will cost more. These lights should be replaced every year or at least every two years. Once your seedlings are up, the lights should be about 2 – 4 inches above the leaves. This can be tricky if you have plants growing at different rates. Try placing a platform under the short seedlings.
For a full explanation of fluorescent lights for seedlings go online to: