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What Makes a Good Potting Soil?
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Greetings!
Last week I mentioned how we fashioned our own potting soil for growing our plants. (Potting soil is also known as container mix, growing "media" or growing "substrate" in the trade.) In the World of Horticulture and Agriculture there are multiple "media" and techniques used to grow each crop.
It's sometimes difficult to see the similarity between an organic farmer growing tomato plants in natural soil using compost and water and a hot house farmer growing tomato plants in artificial media in a computer controlled environment. In both cases, however, plants have the same needs. The roots require water, oxygen, and minerals in a stable environment. Plant growth is maximized when all are readily available.
When you grow plants organically in natural soil, you let Nature take care of the details. The natural fungi, bacteria, and other organisms found in soil will break down organic mulches laying on the soil surface and release simple minerals. At the same time their activity causes granulation of soil particles that become strung together to form a structured environment. These soil organisms create a very stable, nutrient rich, highly permeable "living" soil. Your main input is irrigation.
When you grow plants hydroponically you are in charge of all the details. To maximize oxygen you choose a highly permeable substrate such as perlite, rockwool, pumice, rice hulls, pelletized clay, etc. Highly permeable substrates require nearly constant irrigation. To maximize minerals, you have labs analyzing tissue samples and correcting mineral levels in the irrigation water. To create a stable environment you enclose everything within a temperature controlled greenhouse. Greenhouse growers can and often also maximize carbon dioxide in the air (another way to increase the rate of photosynthesis) and also alter the light levels. All this is usually under computer control. Although quite expensive, hot house agriculture can be profitable if the crop is valuable.
There are warehouses in the middle of cities being converted to indoor farming. Not all of these are intended for growing pot, although Marijuana is responsible for developing much of the technology. One such indoor farm grows fresh greens for local stores and restaurants. They can completely control lighting and temperature and can grow everything to order. They have found that the cost of lighting (with the latest technology) is not much more than a typical office building and being within the city saves much time and money for shipping and handling. OK, back to our subject.
Speaking of materials used as substrates, a number of years ago I read an excellent research report out of Holland concerning the best materials to grow hot house crops with. Holland is the leader in greenhouse technology primarily due to massive government subsidies. The research concluded that the following materials can be recommended for growing crops.
1. Sand (mostly silicon dioxide)
2. Pumice (mostly silicon dioxide)
3. Perlite (aka sponge rock, mostly silicon dioxide)
4. Vermiculite (oxides of magnesium, aluminum, iron, and silicon)
5. Rock Wool (somewhat resembles fiberglass insulation)
6. Pelletized Clay (beads of fired clay)
7. Peat Moss (organic fibers remaining after thousands of years of decomposition)
8. Coconut Coir (fibers from coconut husk decompose slowly)
9. Rice Hulls (from rice mills are mostly silicon dioxide and lignins)
Generally, the supply and quality of these materials is consistent and they are predictable in use.
The researchers wrote that they spent over a million dollars trying to utilize other types of bio mass (materials made from crop residue, discarded wood pallets, mill waste, etc.) They concluded, however, that substrates made from compost, sawdust, bark, or other waste materials weren't predictable. The problem being that most materials aren't uniform enough. They found that one end of a single piece of wood can decompose much faster than the other end. They weren't willing to bet the farm by growing plants in unpredictable substrates.
Unfortunately there seems to be no connection between Dutch research and American nurserymen.
I remember when a major local wholesale nursery discarded an entire batch of Camellia bushes due to a bad batch of bark. Some years before, this grower had decided to grow their plants in the "richest compost". Today many national growers grow their plants (annuals, perennials, shrubs, vines and trees) in a substrate that is nearly all compost. I've seen a lot of container plants from growers in northern states using 100% bark.
About 5 years ago I read an article from a University researcher who promoted the use of bark compost as a growing medium. He stated that the bark must be composted for 2 months adn then is an excellent substrate for a 5 month period. Beyond this period the permeability of the bark declines and root health suffers. It usually takes the grower 2-3 months to grow the product for selling. The researcher recommends that by the end of 5th month the grower must have either:
1) Sold the plants.
2) Shifted the plants into a larger container surrounded with fresh bark.
3) Discarded the plants.
With this in mind, I don't see a good outcome for the purchaser.
This is the reason that we have what I call "florist quality plants" being sold at the majority of garden centers. The plants look best the moment they leave the grower's property. The "soil" unfortunately is nearing, or at the end of its useful life.
50 years ago the the substrate was 100% mineral. My father kept plants in our nursery looking good in the same container for many years, in some cases a decade or more. My father would have to fertilize and prune, but the plants would look fine.
Today, I don't know any major grower that would keep a plant for more than a year in one container before discarding it. Usually after a year, the rootball shrinks, the plant leans and the foliage turns a sickly color. Do growers actually believe that selling and installing the plant will produce a different outcome?
You may not realize that 2 generations ago most of the trees and shrubs sold in the U.S. were field-grown. Trees and shrubs were grown in loam soil in the ground and dug up and wrapped in burlap when sold. In those days only southern growers dared leave container plants exposed to winter's cold. Container growers in the northern areas would have to overwinter their plants in expensive greenhouses. Today northern growers place container plants into slightly larger containers buried in the ground which insulates them from cold and heat (called pot-in-pot production). Unfortunately, these "new" container growers have been taught by "experts" that bark is better than dirt. It is certainly less expensive and substantially lighter than an equally permeable mineral substrate.
Fortunately there are plants that will actually survive being grown in compost. Many trees and bushes grow so quickly that a relatively small amount of compost under them won't be fatal. Most conifers have roots that tolerate lower oxygen levels in the soil and will also survive. Succulents do not require many roots to survive.
If any plant growing in a compost substrate is placed into sandy (highly permeable) soil, it may perform decently. An abundance of oxygen in the soil prevents the compost from going toxic. In clay type soils the results would be poor if not fatal.
Its puzzling when growers can't seem to figure out a contradiction. A major grower sold me some Calla lily plants that died from overwatering. In Nature, Calla lilies grow in bogs! Wet compost often has no oxygen and can produce toxic gasses. Wet sand, silt, clay or other mineral substrates will not rot a Calla lily.
One of the saddest examples we see are container-grown Japanese Maple trees. The bark substrate soon results in a shallow or sick root system and warm weather results in excessive foliage tip burn. Often the experts blame excessive heat or salty tap water. When field-grown Japanese Maples are planted we rarely see foliage problems.
Fortunately it is possible to fix improperly grown plants. I have extracted the bark from the rootballs of dozens of young, container-grown, Japanese maple trees and replanted them into our own soil with excellent results. I have done the same with thousands of plants that were grown in compost-based soils. The only plant that I categorically find difficult to repair are Gardenias. Less than 50% survive the process. (Yet, I also find that Gardenia plants are surprisingly easy to grow when I propagate them myself.) I really haven't lost very many of any other plant that I've worked with. Bougainvilleas have been very easy despite all the dire warning given about their delicate roots.
Washing off the compost with a strong stream of water does the least amount of damage. If the plant is dormant there are no precautions. Of course I keep the exposed roots constantly wet until they are replanted in better soil. If in full leaf during warm weather I would shade the plant for about 2 weeks following treatment or trim off most, if not all, the leaves. Younger or smaller plants are always easier to work with. I usually will replant into a container mix that is 2/3 ACID MIX and 1/3 sand and water immediately. It is no longer amazing to me how good a plant looks immediately after I remove compost from the roots.
After purging thousands of plants over the last 15 years or so I have learned a lot about how plants are grown.
One large wholesale nursery hired a grower from Asia to assist in some of their troublesome crops. The grower would grow his specialties in only peat moss and perlite while all the nursery's other crops were in mostly compost.
Many large nurseries grow or purchase starter plants that are grown in small containers of peat moss and perlite which are then placed into larger containers and surrounded by compost. What I found was an abundance of healthy roots in the center with fewer sickly roots in the surrounding compost.
Large nurseries have uniformly blended soils with uniformly poor roots. Small nurseries must use small tractors as their soil mixes are not very uniform. I do notice that the roots are concentrated in areas of pure soil and avoid areas of pure compost.
The majority of nurserymen don't know much about soil and just use what has been recommended to them by soil suppliers or agricultural agents. The heart of the problem seems to be how research is conducted. Research usually is done over a short period of time. No one pays researchers to find out what happens afterwards. Nurseries funded research to determine the best, cost effective substrate to get plants ready to sell, not what is best for the future performance of the plant.
The best plants available in garden centers are usually bedding plants grown in peat moss and perlite. Unfortunately some bedding plant growers use soils that also contain wood shavings which causes the leaves to be slightly off color.
There are a few growers of larger plants that use redwood sawdust and sand as a substrate. Redwood decomposes very slowly and their plants perform better than most. While not as good as the soil we use, I will recommend them for plants we don't grow. Suncrest Nursery, Pacific Nursery and Otto & Sons are the better growers. Unfortunately it is not possible to distinguish between redwood compost and other wood or bark products by sight. As far as I know only one native plant grower, Las Pilitas Nursery, grows their plants in real soil.
Where am I going with all this?
Well if you want good plants here are your options:
1) Grow them yourself from seeds, bulbs or bare root (no soil to worry about)
2) Purchase migrating plants. Shasta Daisies, Canna Lilies, Mint and many other perennials have rhizomes that emerge outside their original ball of substrate and essentially migrate into your garden soil.
3) Purchase plants that can live in poorly oxygenated soil. Grasses, Conifers, Palms, Impatiens, Hydrangeas, Ficus, and Oaks are among plants that can survive in sewage.
2) Buy plants grown by Laguna Hills Nursery.
3) Buy small plants (1-gallon and smaller) and purge the root systems.
4) Buy larger plants and wash away 1/2 the soil ball. I have found that you can shock up to half the root system of any plant without causing a problem. I am no longer surprised with how few roots will enable a plant to survive.
5) Search for field-grown plants. Most large specimens of palms are field grown. When Disneyland planted trees they found large specimens in the neighborhood and transplanted them.
NEXT WEEK: PLANTING RULES & TECHNIQUES
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GARDEN NOTES
Night temperatures this week have been above 50 degrees F. This allows the roots of truly tropical plants to function better and allow vigorous growth. Plumerias, Bananas, Palms, Sugar Cane, Ginger, Allamanda and quite a few other plants can now start growing vigorously. Basil can now be planted into the ground, but watch the weather reports and cover young plants if the night dips into the 40's. This also means you can leave tender indoor plants outside (if you desire) for the next 5 months.
This weekend we'll have a much better selection of vegetables. Last weekend was supposed to be rained out so we ordered a bit light. Unfortunately our supplier didn't deliver everything we ordered and the weekend was mostly sunny. Result, not enough to sell.
Many of you have requested the bulbing florence fennel. Request granted. This is a multi-purpose vegetable with an edible bulb, leaves, seeds, as well as a place in a butterfly garden (attracts Anise Swallowtail butterflies). It's also perennial.
For the first time this year we have Asian Cilantro (Vietnamese Coriander, Rau Ram) in stock. This is not related to true Cilantro but has a similar flavor. It is used in salads, soups and to flavor duck dishes. Unlike true Cilantro which goes to seed (then dies) easily during warm weather, Asian Cilantro is a perennial trailing herb that can be grown in a container of in the ground in part sun. We are bringing a large sample plant that you can taste.
Many of the 400+ fruit trees we are growing will be ready to sell in a week or two. We will have blueberry plants within a month.
A few of you purchased bare root Forest Pansy redbud trees. These have been unusually slow to leaf out. Two specimens I planted are finally showing signs of growth. Redbuds trees are acting strange this year. Several Chain-Flowered redbuds trees I planted last year finally lost their 2011 foliage and are quite bare at this time. |
EDIBLES AVAILABLE THIS WEEK
Herbs quarts $3 Arugula, Basil, Caraway, Chamomile, Chervil, Chives, Cilantro, Dill, Fennel, Garlic, Marjoram, Mint (assortment), Oregano, Rosemary, Sage, Savory, Stevia, Thyme (assortment), and more
Tomatoes quarts $3 HYBRID Better Boy, Big Beef, Champion, Momotaro
HEIRLOOM Black from Tula (few), Brandywine (original and Yellow), Coustralee, Green Zebra, Pineapple, San Marzano
GRAPE & CHERRY Black Cherry, Grape, Juliet, Sugary
Peppers quarts $3 SWEET Better Belle (green/red), Golden Bell, Orange Sun, Red Knight, Roumanian Ranbow, The Big Early (green/red), Fushimi,
and Purple Beauty (6-pack $3)
MILD Italian Roaster, Padron
HOT Caribbean Red, Jalapeno, Thai
Squash quarts $3 Crookneck Yellow, Zucchinii Dark Green
Other Veggies quarts $3 Kentucky Wonder pole bean, Armenian cucumber, Burpless cucumber, Black Beauty eggplant, Zefa Fino bulb fennel, Swiss chard (few), assorted tomatillos
Other Veggies 6-packs $3 Bulls Blood beets, Rouge de Hiver lettuce (red romaine)
ORNAMENTALS AVAILABLE THIS WEEK
Athyrium nipponicum 'Pictum' JAPANESE PAINTED FERN 1-gallon $12
Calylophus hartwegii 1-gallon $7
Carex oshimensis 'EVERGOLD' SEDGE 1-gallon $9
Coleonema pulchellum 'SUNSET GOLD' PINK BREATH OF HEAVEN 1-gallon $9
Convolvulus mauritanicus GROUND MORNING GLORY 1-gallon $9
Fuchsia thymifolia 1-gallon $9
Gaura l. Belleza Dark Pink quarts $4
Gaura l. Belleza White Evol quarts $4
Gerbera jamesonii TRANSVAAL DAISY quarts $4
Hebe pimeliodes 'Quicksilver' 1-gallon $9
Loropetalum chinense 'Zhuzhou Fuchsia' CHINESE FRINGE TREE 1-gallon $12
Michelia figo BANANA SHRUB 1-gallon $12
Ophiopogon planiscapis 'Nigrescens' BLACK MONDO GRASS 1-gallon $11
Phormium 'Dark Delight' 5-gallon $40
Phormium 'Guardsman' 5-gallon $40
Phormium 'Rainbow Chief' 5-gallon $35
Rose 'Gruss an Aachen' 1-gallon $10
Westringia fruticosa 'Smokey' COAST ROSEMARY 1-gallon $9
Salvia 'UltraViolet' quarts $4 This lovely selection is perhaps a hybrid between Salvia lycioides and Salvia greggii. Expect quick growth to 20" tall and 30" wide with blooming summer-fall. Best in sun in well-drained soil with average to low water.
Scabiosa c. 'Butterfly Blue' PINCUSHION FLOWER quarts $4 This is one of the best perennials. This evergreen plant creates a low clump of foliage topped by mauve-blue pincushion flowers all year! Overall size is about 2' tall and wide. Situate in full sun to part shade. Provide good drainage and average water. Dead head monthly to keep plant tidy and in bloom.
Sedum 'Brilliant' STONECROP 1-gallon $7, quarts (few) $4 Our 2012 crop is ready to sell. We consider this succulent to be one of the best perennials and is very easy to grow. Blooms late summer-early fall with excellent show of pink flowers
AND MUCH MORE! |
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Please visit us at our farmers market locations.
EVERY FRIDAY 9am-1pm
Mission Viejo Farmers Market
Mission Viejo Library
200 Civic Center Drive, Mission Viejo
Exit 5 at La Paz going east, turn right on Marguerite, turn right on Civic Center
EVERY SATURDAY 9am-1pm
Old Towne Orange Farmers and Artisans Market
Historic Villa Park Orchards Packing House at Chapman College
304 N. Cypress Street, Orange
3 blocks north and 4 blocks west of the traffic circle (Glassell x Chapman) in Orange
EVERY SUNDAY 10am-2pm
The Great Park Farmers Market
The Orange County Great Park, Irvine
Exit 5 at Sand Canyon, go south on Marine Way (parallels east side of 5), follow the signs
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26285 Verona Place
Mission Viejo, California 92692
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