Growing and Overwintering Hostas in Containers - Page 2
Warren Pollock, Glen Mills, Pennsylvania
Part 3: 
Terminology
Reference: The Contained Garden by Kenneth Beckett, David Carr and David Steven
Here is terminology used in the British Isles, the mother lode of keen gardening:
potting and potting up - Terms used for setting bulbs, corms, tuber and young plants into flower pots or similar containers with a suitable potting mix. If shallow flats or boxes are used instead of flats, it is known as boxing up.
potting on - The term used when an actively growing young plant, or semi-mature woody plant or herbaceous perennial is moved from a small to a larger pot.
repotting - This term is reserved for taking a well-rooted or pot-bound plant out of its container, removing some of the mix (and often outer roots), and returning it to the same (cleaned) pot or another of the same size with some fresh potting mix.
under-potting - Planting in a very small container. Over-potting is planting in an excessively large container.
Potting Up
   Never put small hostas, especially liners, in an excessively large container; that is, over-potting. My experience is they don't do well and often die.
It is better to under-pot and have hostas root bound than to over-pot.
Potting On
   Move a hosta from one pot size to only the next larger size. Don't jump to a container size that is excessively large for the size of the root mass.
   Sooner or later hostas in containers get root bound and need to be potted on to a larger container. For pot sizes up to about 8 inches, I do this any time during the season. The root ball is easy to handle and I can be careful not to break leaves
   For larger sizes, I usually pot on in early September because if I break leaves then, it doesn't matter as the plants will be dormant soon.
   If pot bound, the roots at the outside of the root ball are carefully untangled. Often one finds that some roots are very long, too long to fit easily into the new larger container. I cut them off with a scissors or pruning shears. The plants don't seem to be worse from it.
Repotting
   In the largest containers, I only repot those hostas that I want to keep in the same containers. Because they are in such large pots, the root balls are big and awkward to handle. Often two people are required, especially to get the root mass out of the containers.
   As I said, I usually repot in early September. I avoid doing it in early season because I always seem to break some of the divisions in handling the root balls, and this means fewer divisions and thus fewer big leaves for the rest of the season.
   I let the root ball get quite dry. Water is heavy, very heavy. I lay the container on its side. The sides of the container are tapped to loosen the ball of soil from the pot. I pound with my fist if the container is small. But for a big container I use a hammer gently since the plastic siding is pretty hard and I don’t want to hurt my hand. I then grab the biggest division or several divisions near the soil, and work the root ball out of the container. Sometimes I need a second person to hold the container so it doesn't move along with the root ball as I pull on the leaves.
   For a ten-inch-diameter root ball, for example, using a long serrated kitchen knife, I’ll cut off about one inch of soil, with roots, from the bottom. [You’ll probably be cutting away a lot of root mass as likely the roots coiled around and around at the bottom of the container.]
If heavily root bound, I also cut away about one inch of soil and roots all around the ball. If not too root bound, to encourage new root growth, I make vertical cuts one inch into the root ball every two or so inches around the ball.
   The root mass is then potted in the cleaned container using fresh potting mix. [Use a 1 part bleach: 9 parts water solution to sterilize the pots' inside surfaces.]
Soil Level
   Pot the roots so the top of the crown is about a third of an inch below the top of the container. Water thoroughly. Because the space between the top of the soil and top of the container is not large, add water carefully at first, filling the space several times until water seeps out the drainage holes. As the soil compacts down, more potting soil is added. You want the compacted soil level to be about a half-inch to an inch lower than the top of the container, enough room for easy watering with a hose thereafter.
Fertilizing
   If the potting on or repotting is done in the spring, I mix slow-release Osmocote with the soil following manufacturer’s instructions. I had been using the 23-month Osmocote formulation, but now favor the 6-month formulation.
Watering
   Immediately after any potting on or repotting, I use "Ortho Up-Start" or similar low-nitrogen/high-phosphate plant starter fertilizer at the rate recommended. These fertilizers contain vitamin B-1 and sometimes a root-growing hormone, stated to reduce transplant shock and aid in early strong root development. To this solution I add liquid kelp, 1 tablespoon per gallon water.
   The bane of container gardening is the frequent watering. The root ball should always be kept moist. If drainage in the container is good - and it should be if you use the proper potting soil mix, one cannot overwater. The key: Water before the root base gets dry so the plant does not become stressed.
Tip: If the soil becomes dry, add a drop (no more) of dishwashing liquid to a gallon of water sprinkle slowly onto the so, or submerge the pot in a bucket of water until the soil is thoroughly wet.
Putting containers on plastic saucers filled with water is beneficial as it provides a bottom water reservoir.
Part 4:
Overwintering - My Way

   The biggest fear in growing hostas in containers is what to do with them in the winter. Different growers have different methods. A lot has to do with where one lives. What works in the South is not necessarily a safe procedure in the North, and Mother Nature is fickle. She can be kind one winter and then produce weather the next year that, at best, can be called "foul," "harsh" or "bitter."
   I live 30 miles south of Philadelphia. My experience totally is in this geographical region. But I bet that what I do is a satisfactory procedure anywhere. (I was going to write “fool-proof”' procedure but I don't think anything in this world is certain – except taxes and death.)

   I put our containers in our unheated garage, usually about Thanksgiving before we have harsh freezing weather. (This date would be earlier in northern regions and maybe somewhat later in southern locations.) Strong wooden shelves along the back of the garage, four tiers high were specially constructed to hold all of our pots.
   The largest containers rest on two-by-fours on the concrete floor which is the bottom shelf. All the containers are watered thoroughly before I bring them into the garage.
   If the soil in any pot gets very dry during winter storage, I add water to it. This is often necessary with the smaller pots such as the four-inch sizes on the top-most shelves where it is the warmest. This is done only on a mild day and when the soil in the container is not frozen. Caveat: Never water a containerized hosta with a frozen root ball. This is a sure way to kill the plant. In the spring you'll find smelly, mushy, rotting roots.
   Given a choice in the winter between over watering or under watering your containerized hostas, always select the latter. Dry roots are not necessarily dead roots; they almost always recover when watered. Rotted roots are dead roots.
   Be assured: The soil in pots in our garage freeze and thaw during winter storage. How many times depends on the weather outside. Our garage temperature is not markedly different from the temperature outside. I suspect that most of the time the soil in the pots freezes slower and thaws more slowly than if the pots were outside unprotected. During one winter, we had at least two dozen freeze-thaw cycles, yet not a single hosta was lost.
   Freezing and thawing does not heave hostas out of containers, if the size of the pot matches the root mass size. (Again, never pot a hosta with a small root mass in a very large container. You'll have problems.) On the other hand, freeze-thaw will heave small hostas planted in the ground in the fall if the roots didn't have a chance to become anchored in the soil.
   What will kill a hosta in a container is having water sitting atop a frozen root mass in a container when the ambient temperature is above 45-50 °F. Here's a scenario to illustrate the problem: A hosta in a container is outdoors unprotected; it is sitting on the ground with no covering. The temperature falls below freezing and the potting mix with the root mass freezes. Then it warms up considerably, and rains. The weather from then on remains above freezing. The soil in the pot does not thaw out immediately; it may take days depending on the size of the pot, ambient temperature and how sheltered the location is. Meanwhile the crown of the hosta is in contact with warm water. Come spring, you’ll likely find the roots rotted.
   To avoid the possible occurrence of this unfavorable situation, I overwinter our containerized hostas in an enclosure.
   De-overwintering must be considered also.. Almost always the shoots in pots will emerge earlier than hostas in the ground. Sometimes this will be months or so before the last frost of the season, officially about May 10 where I live.
   For me, this is a game of moving containers with sun-starved tall shoots and unfurled leaves outdoors into the sunlight when air temperature is above about 45 degrees, and moving the pots back into the garage when the forecast is for temperature below freezing. As I said, it's a chore. But I don't mind doing it.
Stan Alpert's Overwintering Way:
   His garden is in New City, New York, located not far from New York City. He tightly packs his containers in clusters of 200-300 in locations that are sheltered as much as possible from harsh winds, such as along the side of his house. He tries to group pots of the same size together.
The pots are covered with bark mulch or wood chips to a height about two inches above the pots' rims. The mulch/chips are packed tightly between the pots and piled up along the outsides of the clusters.
   He does this around Thanksgiving. If there hasn't been a lot of rainfall, he'll water the piles.
The pot clusters are covered with a “Microfoam” blanket, a thin spun-bonded polymer fabric sold to protect plants in the ground from spring frosts. He says he hasn't seen a difference whether pots are or are not covered with Microfoam, so he may not continue to add the coverings in the future.
In very late winter or very early spring, he removes the plastic covering to allow the shoots to emerge without obstruction.
   Stan Alpert has had no losses overwintering his 1,000 or so pots with this method.
   Mulch or wood chips filling the top of the pots to their rims prevent water from collecting and sitting on the surface of the soil in the pots. They also act as an insulation.
Other Methods:
   Tip the pots on their side and leave outside.
   Remove hostas from the container and place in raised bed with loose, highly composted soil. Top with pine needles or shredded leaves.
   Sink the plastic container in the ground in a pre-frost-dug hole to fit container. Cover the container with shredded leaves, an inch or maybe more.
   Other containers can be grouped together, covered with shredded leaves and then a plastic sheeting like polyethylene can be put over everything. The plastic sheet may need to be removed and then put back on several times in early spring.
Remove Covering
     Remove mulch, plastic sheeting, leaves, etc. when shoots start to emerge. You want as much direct light on the emerging divisions and unfurling leaves as weather permits.

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