Maintenance of Container Grown Plants in the Garden Center

At the January 1982 CNA Short Course, I gave a brief talk about maintaining container grown plants in the garden centers. Several people were nice enough to say they thought it was a good talk, and a few were adamant that I put the thoughts I expressed there down on paper. I placed a summary of that talk in “Additions to the Plants We Grow” and also decided to include it in this book with some additions from the talk I gave at the New England Meeting in February 1986. Most of this material will be ‘old hat’ to those that have been in business for some time. However, I hope some of the information will be useful for those who are new to the garden center business.

As soon as new plants are received in the garden center, the person in charge should immediately check to see what type of media the plants are growing in. Different growers use different media. The most important factor that the garden center operator has to take into consideration is how well each of these media retain water and absorb water when irrigated. Some of the bark mixes, which are so popular with many growers today, dry out extremely fast and have to be irrigated much more often than the sand-peat mixes that were so popular a few years ago. It is only by being aware of this problem, and by trial and error methods of irrigating and then allowing the plants to dry to a certain extent, that a garden center manager would be able to tell just how much irrigation is needed for the plants of different suppliers. Another factor that should be taken into consideration is the practice of many growers now buying in plants from other nurseries and reselling. This means you could be getting several different types of media in one shipment. Therefore, the media should be checked on different varieties of plants, especially if different types of containers are apparent in the shipment. All of the above isn’t nearly as critical in the spring when the plants are dormant as very little water is used at that time, but just as soon as the weather becomes warmer and growth starts, water use increases immensely and this is when plants can be lost unless the above mentioned considerations are met.

Container grown plants are somewhat like the “three bears’ chairs” in Goldilocks — some are too large for the container they are in; some are too small for the container they are in; and some are just right. If the plants are too small, it is generally because the grower had a problem with his crop the preceding summer and had to either ship plants that hadn’t done well or plants that should have been held longer before going into the sales yard. If you receive plants like this, obviously some discussion with your grower is in order. There are exceptions to this — some of the summer flowering shrubs such as Potentilla or Spiraea that will probably not be sold until they have put on a flush of growth and come into flower, or Japanese Red maples that will not be sold until they put on a flush of growth. If these plans are shipped at their optimum size, they will be over optimum size in relation to the container at the time of sale–the same type of problem I will mention below. Also, dwarf conifers at times look small for their contained size primarily because their root system is more extensive than their very slow growing top.

Plants that are too large for their containers, at first glance, appear to be a “good buy”. However, because their root system is too confined for a large top, they are extremely difficult to keep watered, not only in the garden center but after they are planted. These plants can be extremely root bound — fibrous rooted plants such as rhododendrons and azaleas can form a root ball that is almost as hard as a rock and just about impenetrable. Long rooted varieties such as Cotoneaster or pyracantha can spiral their roots around the container until they are practically strangling themselves. It’s my opinion that plants of this nature are the ones that cause the myth that container grown plants do not do well when planted out. Some plants, if in the container too long, will never again have any value; and others, before they can have any value, must have their root systems altered by either cutting or by another type of manipulation, and their tops cut back so that the root system can maintain it.

The plant that is just right for the container has roots that are out to the edge of the container but not spiraled around it. There should be enough root system to maintain the top — not so much top that it cannot be maintained by the roots in the container mix. Plants of this nature, coming into the garden center in the spring, need only to be spaced and given adequate water through the springtime months up until they are sold or the time growth starts. As growth first starts, it is important that the plants be spaced well enough so that the new growth is not smothered.

In most areas, by early June, it is hoped that all the plants purchased for resale have been sold; therefore no more maintenance is required. However, this is a dream that very rarely comes true. The ratio of different species and varieties that are sold one year very rarely is repeated for another year; and therefore, although certain varieties may be sold out entirely, the garden center operator is usually left with a rather large surplus in others. This is when the garden center operator has to think of himself, not as g retailer but as g grower, because container grown plants are ready to grow in a normal manner just as soon as the weather conditions are right. At this point, you are not in a maintenance situation but in a GROWING situation. Therefore, the garden center operator, having set aside the few plants he feels he might sell in late June and early July, should think of handling his leftover container plants the same way a grower would; primarily, this means putting them into a larger container and growing them on.

The steps outlined below are the minimum advice I would give for the neophyte retailer. Most garden center operators should know most of this information already.


1) TIME TO DO THE KICKING UP — the earlier the better. You should repot as soon as you realize that you will have to carry material through the summer, certainly, I would hope before mid-June (see below under Pruning and Disadvantage of “Kick Up” the reason for this early kick-up time.

2) TYPE OF CONTAINER — whatever kind you can lay your hands on the easiest and as long as it looks clean and has not had diseased plants in it previously. It should be one size larger than the container the plant was in when you bought it. You should put a one gallon into a two, etcetera. ‘

3) TYPE OF MIX — keep it as simple as possible. I would recommend one part sand, the sharpest you can get, and one part Canadian peat. It can be mixed in an old cement mixer; or if your quantity is not too great, by hand on a. hard surface. Sand and peat give good drainage, enough weight to hold the cans upright, and should have a minimal amount of weed seed. The ready-made mixes, such as Pro-Mix, are fine except all of them I know of are too light when dry and your plants will tend to blow over between irrigations as they get larger later in the summer.

4) ACTUAL MECHANICS OF KICKING UP — Whether you put the soil mix on a bench or work out of the soil pile is up to the individual garden center. The plants should be just tapped out of the container they are in and placed in the new container, making sure the soil level in the new container does not come above the soil level present in the old soil ball. The mix should be pressed tightly down in the area between the old soil ball and the outside of the new container so there are no air pockets. If the plants being ‘kicked up’ have been grown correctly, there is no need for anything to be done to the roots; however if they have been in a container too long, the roots should either be cut or manually raked out so that they will be able to penetrate into the new media and stop any coiling.

5) FERTILIZATION — Unless the garden center already has an extensive liquid feed fertilization program which is used on the ball and burlap material as well as containers, I would recommend a dry, slow release type fertilizer placed on top of the mix. I prefer Osmocote myself and would use the full rate recommended for everything, except one-half rate for ericaceous plants.

6) PRUNING — The quite drastic pruning or shearing that is sometimes necessary for these plants after they have been kicked up is a subject that is too long to go into now, for each variety has to be handled individually. However, just about all ‘feathered-out’ growth should be taken off almost all varieties. If in doubt about how hard to shear, I would suggest contacting the grower to see how he handles the variety in question. A later shearing, some time in mid-summer, may also be necessary.

7) INSECT AND DISEASE CONTROL — Just as a grower, you are going to have disease and insect problems with these plants. More than likely, one of the all purpose insecticide and fungicide combinations that you would be selling to a homeowner would solve most of your problems.

8) WEED CONTROL — Unless you have a million of these plants it will probably be best to hand weed — be sure to get somebody in there at least once a week to go through them. If weeds in a contained get too larger, it is sometimes necessary to throw away everything as the weed cannot be pulled away from the plant without destroying the root system of the plant being grown.

9) WATER — Irrigation for container grown plants during the growing season is necessary every sunny day — this means weekends, weekdays and holidays.

10) SUN — All plants, with practically no exceptions, should be grown in full sun and spaced well enough apart for good air movement. Growing them in a shady location will only lead to disease problems, leggy growth, and poor plant material. Of all the varieties we grow here, the only ones that are grown under shade are the ferns. Even plants that we feel will tolerate shade produce a more salable plant if grown in full sun. Full sun, of course, means they require adequate water. The two go hand in hand.

11) DISADVANTAGE OF “KICK UP” (This could also be entitled “When to Sell”) — The great disadvantage of kicking up plants in this manner is that they really should not be sold for about two months. Heavy pruning can make them look pretty ugly for a while. But most important is the fact that the root system takes about two months to get out and solidify itself into the new mix. If the plants are sold too early, the customer will tap them out of a two-gallon container and find that the soil ball is the size of a one-gallon container and will obviously feel that they have been cheated. Also, the plant will be set back by having the new roots that are just starting to move out into the mix damaged by this treatment. This is one of the reasons why the ‘kicking up’ operation should be done in mid-June so that the plants will be established in their larger container in time to be sold in late August and September; the optimum time for fall planting.

12) ADVANTAGES OF “KICK UP” — The economic advantages should be obvious. A one gallon plant purchased in the spring would probably be almost worthless if carried through the summer in the same one gallon container. That plant, kicked up to a two gallon, would probably have a retail value in the fall four times the original cost. Taking into consideration the effort that has to be put into growing such a plant, the profit on that two gallon would probably be about the same as if you bought it; however by avoiding the almost certain loss if kept in the one gallon container, the profit will be greater on the “Kick Up” plants. The other advantage is that in the fall the garden center will have good looking nursery stock to go along with the new material that has been purchased from your grower.

If you have some container material still unsold that you have to carry through the winter, I personally would suggest a quonset-type holding house such as most of the growers in the northeast are using; bent 3/4 inch pipe, 3 feet apart seems to work well in our area. The house, obviously, can be made in any increments of 3 feet depending on your needs. A 21 foot length of galvanized pipe, bent in the half circle arch, will make a house 14 feet wide. Don’t try to sneak out a couple of extra feet as that flattens the top of the quonset and makes it susceptible to collapse under a snow load. Six mil, clear polyethylene shaded with a bit of cheap latex paint thinned in water should work well. A layer of clear, thin 2 mil polyethylene laid over and tucked in under the bottoms of the tender-rooted plants such as Cotoneaster and Ilex will hold the temperature even higher than the temperature within the quonset and give extra protection to tender roots which can die at 20 above zero. irrigation within the quonset is necessary three or four times throughout the winter and inspection of the stock should be made at rather frequent intervals, especially in late February and early March when excessive heating of the quonset and drying out can occur. Remember — if you vent to cool the houses you also lose moisture. Once again, this is a situation where you have to think like a grower, and a visit to your grower to see how he maintains his plants through the winter should give you many ideas on how you can best handle the problem.

As I said earlier, the talk I gave at the Short Course was a brief one, and the points that I have mentioned above are what I consider minimal. If any of my customers feel that they have problems with maintaining, growing or over-wintering their container grown plants and the answers to their specific problems aren’t in the above, I would be more than glad to discuss these problems with them and see if, together, we can come up with some solutions.

I f a butcher sold tainted meat, he certainly wouldn’t stay in business very long. Likewise, a garden center that is selling off color, unpruned, root bound material is also going to be in trouble. By presenting only well-grown, first-rate material to the public, the garden center operator not only enhances his own business but elevates our whole industry. It is an effort to which we should all apply our best thought and energies.