Hostas in Containers

To start with, we do not recommend growing hostas in containers.  Obviously it can be done, we grow thousands of pots here every year, but we also lose some of them every year.  It may be just a few, it may be hundreds, but we know there are going to be losses.  So if you're going to grow hostas in containers, you have to accept the fact that one or two or all of them might die.  If you have a conniption every time one of your plants dies, and especially if you want us to replace it, then just don't try it.

The most common causes for failure of container grown hostas are poor drainage and late freezes, both of which can lead to crown rot.  Just remember that when the plant goes dormant in the winter it does not need care, it needs protection.  There is virtually nothing going on inside the plant during dormancy, so all you need to do is stop bad things from happening. 

It really isn't as hard as we might make it sound.  If you're trying it for the first time, we recommend you use the less expensive varieties, and you should probably stay away from blue varieties, which seem to be the hardest to grow in containers. Just be realistic and remember that Mother Nature didn't design the plants to grow in pots, so you have to provide for them and accept the risk.

Most of the information below applies to cold winter areas.  I have no experience in areas where it does not freeze, so you are on your own there.

Watering

As with just about every aspect of hosta growing, water is a key factor in growing in containers.  Potted hostas in active growth will almost always require hand watering, at least in the summer.  How often they need watering will depend on the size of the plant, the size of the container, the type of soil, and whether they get natural rain.  Just water them often enough to make sure they have plenty of moisture available during the spring and summer, and never dry out when they are in active growth, that is, the entire year except during winter dormancy.

During dormancy, the plant should be kept just moist enough to prevent the soil from drawing the water out of the plant.  The plant is not using water at this time, so you do not need to add any unless the soil is dry to the touch.

If you leave your pots outside during the winter in the rain and snow, the water in the soil will freeze, forming a solid plug even after the top of the soil thaws.  If more water gets in the pot it cannot drain and the crown will sit in water, leading to - you guessed it, crown rot.

Potting Soil

Choices here range from whatever you can shovel up in the yard to bagged potting mixes.  I would always recommend a commercial potting mix, preferably a mix that contains more than 50% composted bark. Our preferred mix contains 60% bark, 20% peat, and 20% perlite/vermiculite. Some growers use up to 100% bark. If you are going to keep a hosta in a pot for more than just a short time, drainage is extremely important.  The temptation is to use a heavy mix that holds a lot of moisture so you don't have to water so often, but if you use a poorly drained mix, heavy on peat, compost or dirt, your hostas are likely to - here it is again, rot.

Fertilizing

I recommend a light touch with the fertilizer, probably a maximum of half of what the directions recommend.  We stop feeding in early August here because we don't want to encourage late growth before cold weather.  Make sure you drench the plants heavily to wash out any salts occasionally, especially before winter.  I recommend a balanced, general purpose fertilizer, but I don't think it matters much what kind you use. Using too much or fertilizing too late can lead to you know what.

Containers

Hostas do not like to be over-potted.  We recommend growing in the smallest container that is practical.  We say practical rather than possible, because the smaller the container, the more often you will have to water it and the sooner you will have to either divide the plant or pot it up.  We start a plant in a 3½" pot if it will fit, then move it to a 4½", then a gallon, then, after a year or two in a gallon, to a 2 or 3 gallon pot if the plant requires it.  After quite a few years, we end with a 3, 7, 15, and up to a 25 gallon pot, depending on the plant. 

It seems like a lot of trouble, and maybe it is, but putting a small plant in a large pot seems to be the easiest way to fail in container growing.  Even if the plant seems to thrive during the summer, there is a very good chance that it will rot over the winter.

Over-wintering

Our over-wintering program starts before the plants go dormant.  We try to make sure the plants go into winter well watered, with the soil moist but not wet.  We leave the plants in unheated hoop houses covered with white plastic. 

We also grow plants outside in containers.  We cover these with a thermal blanket so they don't continually freeze and thaw, covered with a layer of white plastic to conserve the moisture in the pot without letting additional rain or snow get them too wet. White plastic is better than clear because it reflects the sunlight.  If you are holding plants in the shade, clear is probably fine.  In the spring, we uncover before the plants break dormancy to avoid the leaves coming up under the plastic. 

Since most of you do not have access to cold frames and thermal blankets, a reasonable alternative would be an unheated garage or a covering of leaves or other insulator outside.  If you leave your plants outside and cover them with leaves or straw, either cover the pile with plastic or put the pots on their sides so water can't get in.  I would suggest including an ample supply of mouse bait with the pots to keep the mice from feasting over winter.  Check the bait supply frequently and make sure you uncover the pots before the leaves come up.

Other than the possibility of being eaten, almost all losses occur during the winter or very early spring, and the cause is almost always crown rot. Spring is the worst time for us.  We usually get quite a bit of rain or snow in March and April after we uncover, and that's not a good thing unless the plants have broken dormancy and the leaves are growing.  Plants break dormancy earlier under the plastic than in the ground, so we usually have to uncover them before we would like, and we almost always have late freezes after the plants break dormancy. 

Ah, the late freezes.  If a hosta freezes after the leaves start to unfurl, there is an excellent chance crown rot will set in.  At the very least, the leaves will turn to mush and it will be weeks, maybe a month, or even more before it looks good again. If a late heavy frost or freeze is forecast, we have to heat the cold frames and recover the plants in the field.  Our plants have to look good early in the season, so we have to try to avoid even minor leaf damage. Covering and uncovering thousands of plants is a colossal waste of time, especially when the forecast is almost always wrong, but every time we take a chance we get burned.  You may not have to worry so much about frost, because the plants will recover, but it might take a while.  If a freeze is forecast when the hostas have even partially open leaves, you should protect the plants.

A hard freeze often leads to crown rot, especially in blue varieties, and especially if the soil is wet.  In a large plant, the rot may only affect part of the crown and the rotten part can be cut away.  In smaller plants, it is usually fatal.  If the leaves are still furled in a tight, pointed spear, hard to the touch, they can probably withstand a hard freeze with no damage, but if they have started to open only slightly, don't take a chance.