Editors Note: This is a Classic Article, and was originally spread over four The Hosta Journal issues beginning in 1994. It is assembled here as a single article with four sections. Warren has updated it in some places to make it more useful to today's readers. Warren and Ali Pollock have been iconic figures in hostas for several decades and the garden they once shared is gone now. Nothing defined their Wilmington, Delaware garden more than the fantastic collection of hostas in pots found mostly on their driveway. Warren's past mastery of the art of growing hostas in pots is unequalled today, and this article reveals many of the secrets of his success.
Growing and Overwintering Hostas in Containers
Warren Pollock, Glen Mills, Pennsylvania
Part 1: 
Why Grow Hostas in Containers?
   In 1992. Ali, my wife, and I had one hundred sixty-seven hostas growing luxuriantly in containers in our garden, and we moved all of them to a protected location in late fall. In 1993, we had one hundred eighty-one containers with hostas, again overwintering them. This summer, 1994, we had one hundred forty-seven hostas in containers. They will be moved to a sheltered location for the 1994-5 winter.
   We are not in the nursery trade. We have neither a greenhouse, polyhouse nor sun porch (conservatory)
.
   We have tree root problems that markedly limit where we can satisfactorily grow any perennials. There is an extensive network of greedy maple and other tree roots in both our front and back yards. In time, hostas lose out in the competition for water and nutrients, regardless of how well the soil is prepared prior to planting and how well the hostas are watered and fertilized.
   In addition, the large number of tall deciduous trees with their big leaves cast dark shadows almost everywhere all day. The earthen areas on our property that get enough sunlight to grow hostas satisfactorily are very limited. Heavy shade and aggressive surface roots from trees are among the worst conditions for growing hostas luxuriantly.
   Another reason is what I call "staging." Sometimes you want a hosta in a certain dramatic location but if planted in the ground, the clump height is too low for the landscaping effect. Making a high-enough mound of soil for the plant to be planted in is not satisfactory. So the hosta is grown in a container to raise it to an eye level that compliments the surrounding planting. Often this container is very large and not moved for the winter.
   Yet another reason is that young hostas, especially tissue-culture liners and difficult-to-grow varieties can often be best started in containers and grown on until they reach a suitable size for planting in the ground. And, if one is growing new cultivars for critical observations and side-by-side comparisons with other hostas, having them in containers where cultural conditions can be controlled is an advantage.
   We have one hosta growing in a ceramic container. It is the small H. gracillima with long, narrow, wavy, green leaves. The glazed pot has drain holes and is decorated in a Chinese blue design. There is also a matching saucer. The hosta and pot complement each other nicely and make an interesting accent piece on the railroad-tie retaining wall of our patio.
   The rest of our hostas in containers are in plastic pots. These pots are lightweight, just about unbreakable, very long lasting and cheap...usually free. Although there are some very attractive decorative terracotta-looking plastic containers on the market today, I prefer the green or black pots used extensively in the nursery industry. I think these colors look better with hostas than terracotta.
Additionally, for several reasons, I prefer the width of the pot to be greater than the height. First, my experience is that hosta roots mostly grow out laterally, and I want as much space for them to do this before hitting the walls and having to bend downward. Second, it takes longer for the hostas to become root bound in wide pots, so potting up is less frequent. (But don't put a very small hosta in a very big pot regardless of the pot's proportions.)
   Further, I think wider-than-tall pots look better with hostas because most have leaves that spread out laterally or are fan shaped. The Tiara group, e.g., 'Golden Tiara', 'Diamond Tiara' and 'Golden Scepter', look very nice in such containers.
   These pots are not easy to find and I have only a few. I make a practice of frequently examining the discard bins of local nurseries for them. One nurseryman calls them "azalea or rhododendron pots." Some containers intended for water gardens have these proportions.
   Big plastic pots used for trees and shrubs often are this proportion or have a height about equal to width. I look for the ones with handles molded in. Our biggest plastic containers are about twenty-four inches wide and fifteen inches high. Two sit permanently in special locations in the garden.
I find that plastic containers about fifteen inches wide and high are about as large as I can move to a sheltered area for overwintering. We have huge clumps of H. 'Sagae' and 'August Moon' clumps in them.
   These pots are sturdily built and have two handles molded into the sides. Two men can move them without much trouble even when the soil is water saturated. If I don't have someone to help me, I let the soil dry out a bit, rock the container onto an old piece of carpet, and then drag the rug with the pot on it.
   Most of the containers are considerably smaller and I can handle them by myself even when saturated with water. What the nursery trade calls "pint" is the smallest size. The new, small, single-division hostas are planted in them.
   One interesting container to consider is the bowl sold for storing a garden hose. They are about nineteen inches in diameter and nine inches high, and available in most garden centers and garden-related mail order catalogs. Although there's a hole in the side for the hose to go through, additional holes in the bottom should be drilled to assure good drainage.
Part 2:
What hostas to grow in containers?

   Any hosta can be grown in a container.
   That said, I must quickly add that one cannot get as big a clump size in a container as in the ground simply because containers have limited growing space. I think roots not being able to spread out laterally, as they do in the ground, has something to do with it too.
   Practically speaking, the potential size that a hosta can reach in a container will be limited by the size of the container. In a home garden, container size is limited to what one or two people together can handle. I'd say it is 10 gallons, about 15" x 14 1/2".

   A 15-gallon container, about 17" x 15", would probably require some mechanical equipment assistance. These big sizes are often called cans or baskets in the nursery trade.
   All smaller size hostas do well in containers, and there seems to be no restriction on how large a pot they can be grown in. The Tiara group, for example, does particularly well. We have had 'Golden Tiara' in 3-gallon containers bigger in size and better looking than the same-age hostas in the ground. Likewise with 'Platinum Tiara', the white-edged gold-centered form of 'Golden Tiara'; 'Golden Scepter', the all-gold form; and 'Grand Tiara', the wide-margined sport.
   With just a few exceptions, all the bigger size hostas do well in containers, say two gallons and smaller, when the hostas are small. H. 'Great Expectations', interestingly, is one that I have not been able to grow well in pots greater than two-quart size. I seem not to be the only one who has made this observation with 'Great Expectations': I've heard the same problem from a wholesale nurseryman.
   Therefore, the key question should be: What hostas do well in large size containers, say, 3- or 5- or even 10-gallon size?
   By well, I mean that the hostas will get to about the same size and be as luxuriant as grown in the ground, assuming good cultural conditions, for about the same length of time. This implies the containerized hostas were potted up (properly should it be “up potted”?) when they became root bound.
   My experience indicates that any hosta can do well in large containers and reach a fairly large size – except many, if not most, of the H. 'Sieboldiana' types. I have not been able to get 'Elegans' to a large size, nor also 'Northern Halo'/'Northern Exposure', 'Great Expectations', 'Tokudama', 'Tokudama Aureonebulosa', 'Tokudama Flavocircinalis', 'Golden Bullion' and 'Golden Medallion'.
   Some time ago I stopped trying to grow the sports of 'Elegans' (such as 'Frances Williams'), 'Tokudama' or any hostas with strong H. sieboldiana lineage in large containers. I think it has to do with the thick ropelike roots and their being confined. Perhaps one should root prune these hostas each year as was done with fruit trees growing in containers in the opulent days of Louis XIV.
   Some big hostas that I have been able to get to a fairly large size in large containers include H. 'Sagae'; H. ventricosa 'Aureomarginata'; H. montana 'Aureomarginata'; 'Fortunei Aureomarginata'; 'Gold Standard'; 'August Moon'; 'Sugar and Cream'; 'Sweet Standard', the streaked sport of 'Sugar and Cream'; 'Blue Angel'; 'King Michael’; 'Antioch'; and 'Daybreak'.
Potting Mix:

   There isn't too much written on potting mixes for overwintered perennials, especially in large containers that remain in the same containers for many seasons, say five to ten years. It's a subject that most writers of books on growing plants in containers skimp words on. That's because, for the most part, the information in the books is intended for one-season containerized plants or for house plants. Yet other than watering, the potting mix is just about the most important aspect of growing hostas in containers.

   The ingredients can be infertile because fertilizers are always added.
   In the Virginia and Carolina areas, a common potting mix used in the nursery trade is 6 parts ground pine bark, usually somewhat decomposed, and 1 part coarse sand. I question whether the sand is needed. Some say it's there to improve drainage, but I think it just adds weight to the pot for stability of tall growing plants such as shrubs and trees on windy days.

A premium potting mix should have:

  • easy root penetration,
  • good air circulation
  • good drainage

The mix I use is 3 parts Jungle Growth potting mix and 1 part coarse grit

   This bark potting mix is lightweight and does not compact. it has a very open, porous, crumbly structure. Air and water are easily captured in the voids. Drainage is good. In time the bark breaks down; drainage decreases and water retention increases. I’m told it takes about four, maybe five, years for the bark to more or less fully decompose in a heavily rooted pot that's abundantly watered and fertilized.
   Hosta roots love this bark potting mix. A massive fibrous root system easily develops. As long as the pot is watered frequently, perhaps twice a day in the South, and fertilized frequently, perhaps as often as once a week or more, this may be as ideal a potting mix as one can find.
   When one takes a hosta out of a container with this mix, the bark (and sand) can often be shaken from the root ball. Sometimes I've noticed that the roots actually attach themselves to the bark pieces. (There is some question as to how well plants grown in this potting mix do when planted afterward in the ground.)
   Jungle Growth is a blend of composted forest products (bark) for non-compaction, Canadian peat moss and vermiculite for moisture retention and perlite for aeration. There is also some granulated charcoal.
   I'm sure there is nothing magical with Jungle Growth that can't be found in other commercial potting mixes that contain composted bark. There are brands with composted bark available throughout the Northeast. A nursery supply firm may be a better place to look for them than a general garden center.
Author's Comments:   [For more than ten years I have not found Jungle Growth in my local nurseries and garden centers. Probably because of a superb marketing effort along with a comprehensive nationwide distribution network, they mostly only offer products from the Scotts Miracle-Gro behemoth. So I went over to using “Miracle-Gro Potting Soil” because it is readily available in super large bags and heavily discounted in big-box stores. It is largely peat moss with perlite, which I don’t like because of its too-noticeable white color. But all in all it is a good soilless mix. Though it contains some fertilizer, the amount is not enough for hostas and must be supplemented. ]
   [Recently my preference has been a fairly new product called “Organic Mechanics Container Blend Potting Soil.” It is 100% organic and has no peat moss. It contains compost, pine bark, coir (coco fiber) and, interestingly, worm rice hulls. This soilless mix doesn’t break down as fast as peat-based mixes, holds moisture well and has excellent drainage. You do have to water often. Availability is somewhat limited. Check it out on the Internet: www.organicmechanicsoil.com .]
   The grit adds further drainage and air retention. Although Miracle-Gro doesn’t need grit if plants are in containers for only a year, maybe two. My experience is grit is needed if kept longer because the peat then breaks down and drainage markedly decreases. 
   By grit, I mean chicken grit, crushed granite sold as a supplement for feeding poultry. I buy it in 50-lb bags. The brand name is "Gran-I-Grit" and comes in several sizes. The Starter size, I think, is too fine; I use the Mid-Grower size.
   A soilless potting mix containing one-quarter grit is a heavy mixture. A water-saturated 10-gallon pot is just about too heavy for me to lift. Perlite, vermiculite and polystyrene beads are all feather weights in comparison to grit, which is a reason why mixes containing them are popular with both home gardeners and the nursery trade.
   In a bushel-basket-size container of the potting soil, I add fertilizers and other “goodies.” If potting is done in the spring, I add a small handful of a controlled-release fertilizer, "Osmocote," readily available in garden centers. About half of the handful is "13-13-13 Plus Minors" stated to last up to 4 months. The other half is "17-6-10 Plus Minors" claimed to be "270-day Foolproof Feeding." [Product labels have changed over the years. Still, you’ll probably find the current labels have about the same nutritional contents. My experience indicates Minors or trace elements are beneficial, so look for fertilizers with them]
   I also add two big handfuls of greensand. This is mined in New Jersey and fairly easily obtained where I live. It's a marine deposit with potash, silica, iron oxide, magnesia, lime, phosphoric acid and numerous trace elements. [Pete Ruh in Chesterland, Ohio, extolls it and he grows great hostas.]
   I further add a handful of black rock phosphate. Black rock phosphate contains only 4% phosphoric acid. That's not much phosphorus so I add two handfuls of bone meal (1-12-0), or a small handful of superphosphate (0-20-0), or a half of a small handful of triple superphosphate (0-46-0).
Then I add a handful of powdered kelp, sea weed. This elixir is supposed to stimulate growth and improve stress resistance. Organic gardeners swear by it – and so do I.
   Finally I add a half handful of alfalfa meal.
   Added to the solution is half-strength “Peters 30-20-20 Orchid Special.” I don't use "Miracle-Acid" 30-15-15 or generic equivalents for acid-needing plants. The pH is too acid. I sometimes use regular "Miracle-Gro" or generic equivalents with 15% nitrogen at full strength. [I want a quick acting fertilizer – but not too much of it.]
   To each gallon I also add 10 drops of “Superthrive,” another tonic with great claims: "all essential vitamins, hormones and other extra factors."
   Also added to each gallon is 1 1/2 tablespoons of the systemic fungicide “Bonomyl” from Bonide, which is similar to “Benlate.” [Benlate is not available anymore, nor is Bonomyl. Bonide's new consumer product is called "Infuse". The general purpose, fungicide “Cleary 3336” can be substituted.]

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