How to grow roses: Growing roses in containers
Select a size of container that matches the anticipated size of the rose one wishes to grow – water-holding capacity is central to success. In principle, a pot that holds 10 litres of water would suffice for a Miniature rose; a Bush Rose needs a water-holding capacity of at least 20 litres; and a large Climber needs a tub or drum with a capacity of at least 50 litres. On the other hand, three and even more roses can be planted in one large container, as long as each bush still has a soil volume of 20 litres.
Pots may be plastic, asbestos, concrete, wood or metal.
Container roses are expected to be feature plants, so it is advisable to select showy varieties that are vigorous, free-flowering and that develop a good plant shape. A tall-growing rose looks better in a tall container, and a bushy variety in a more compact container.
Ground-cover plants look attractive planted round the edge of the tub; and pebbles or bark chips make good mulch.
It is essential that the container has good drainage holes at the bottom or at the lowest point on the sides. With holes at the bottom, the container should stand on bricks or similar supports, not on soil or lawn, which could block drainage holes. The practice of placing pebbles, potshards, stones or similar material at the bottom is advisable, since it ensures long-term drainage.
The soil used should offer good drainage on the one hand, and water-holding capacity on the other. Ordinary potting soil is not good enough, since it will settle and compact after a year or two. A good mix is: one part garden soil; one part potting soil; one part pine bark mulch; one part pine bark chunks, or pecan nut shells or similar material; one part gravel or clinker ash; one part coarse river sand; and one part peat moss or peanut shells.
Plant the rose, making sure that soil level is somewhat above the rim of the container, and not settled too deeply. Water thoroughly until the water is running out at the drain holes.
Watering is now the key to success. During the first two months, water only every second or third day. After this period, the roots of the rose will have spread in the container, and it is now important to water every day. Water must be sufficient just to reach the bottom drainage holes. With less water, the lower parts will dry out, the peripheral roots will shrivel, and the rose will soon be riddled with spider mite – and could eventually die. Watering can be reduced during winter to twice a week, but the rose should never be allowed to dry out.
Spread a tablespoon of a rose fertiliser every three to four weeks per every 20-litre volume.
Normal pest and disease control applies. However, especially, in the more controlled environment of a container, it is useful to drench early in spring with an insecticide of the active ingredient imidachloprid. This takes care of insects for about six months.
Although roses can perform well for 6 to 10 years in a container, if it is found that vigour and flowering is lacking, water takes too long to arrive at the drain holes indicating soil compaction the rose plant can be pulled, levered out of the pot and replanted with fresh potting soil. Alternatively, a strong stick, steel pipe or crow bar etc. is pushed all the way down to the bottom a few times and such tubular holes are filled with a water holding compost mix.