By: Ronald Schwerdt, 2-8-03
If you would like to have miniature roses growing indoors during the cold winter months when the snow is deep over your rose beds, late fall is the time to get organized. Almost everyone has a window or corner in the house somewhere; a few miniature roses can be grown under lights. Here’s how to collect roses from your garden for indoor excitement!
The best time to prepare the roses that you want to grow indoors is when plants are going into dormancy. First off, refrain from removing spent blooms from the selected plants. This helps your plants go into dormancy. The petals on the blooms will generally fall off in time, leaving the rose hips. Had you pruned your roses as you did during the summer, the plant will think its time to start into a new growth cycle.
The miniature roses you want to grow indoors need to be dug up and transplant into containers. I use 6″ plastic pots that have sufficient drainage holes. Transferring roses from your rose bed into containers should take place when the soil can still be worked, and just prior to the ground freezing. The longer you hold back the better. The best time for a plant to be moved is when it is semi-dormant.
If possible, keep the soil ball intact without disturbing the root system. Once in the container, the plant and container is given a good flushing with water. Water the container until the water flows from the drainage holes.
At this time, the plant and container are sprayed with a combination of a fungicide and an insecticide. I use Funginex to protect the plant from black spot and powdery mildew, and Orthene as an insecticide. Spray until the foliage and stems are dripping. This will eradicate any bugs or eggs intending to hibernate on the plants over the winter.
Generally about mid-November the plants need winter protection:
- The containers are set into some type of cold frame (this is no more than some type of enclosure that protects the plants from the direct blast of cold air, the sun, or a build- up of snow on top of the containers during dormancy. It is not that snow is bad for the plants, it’s just not desirable at this particular time.).
- The plants may be buried in the garden and covered with leaves.
- Containers can also be set in an unheated garage or placed in a second refrigerator used during the summer to store rose blooms. The refrigerator should be set at about 35°F.
The roses stay in this dormant environment until mid-January, when they are brought into the house to start a new cycle of growth.
January is the time to bring in your roses for winter forcing. After a couple of days inside, the soil will have thawed and warmed up. Wash off the pots and prune the plants down to 3 to 4 inches, and set them under your lights. In 40 to 45 days the plants should be coming into bloom. Increasing the light intensity, along warmer temperatures, will result in quicker blooming.
By growing the minis under light you will be able to produce the finest disease-free miniatures you have ever grown, since you are in complete control of the environment in which they are bring grown. Once you understand the principles of growing under lights, the actual physical part of growing them is relatively simple. Let’s consider the various elements of that environment.
LIGHT Light when combined with fresh air, water and organics in the soil helps produce food for the plant. This is known as “photosynthesis”, and affects the quantity as well as the quality of the blooms. Miniature roses require high light energy; it is their #1 requirement. This can be achieved by various means:
- Increase the number of lamps
- Grow the plants closer to the light source
- Provide some type of reflecting material above the lamps and on the sides of the fixture.
Light intensity is measured in foot candles (f.c.). The longer the fluorescent tubes the higher the light intensity. Plants receive the most light intensity when they are directly below the center of the lamp. Light intensity decreases by 20% at the ends of the lamp. If the plants are set off at an angle to the lamps the light intensity is also decreased. By rotating the plants under the lamps, you will assure that all sides of the plant are receiving the same amount of light, resulting in a fuller, more symmetrical plant. Very good success with miniature roses is obtained when the light intensity is in the 1400 to 1500 f.c. range.
The necessary wavelengths for plants to grow are blue, red and far red. The standard cool-white fluorescent lamp emits blue and red light energy. These wavelengths are necessary for proper foliage development. The standard warm-white fluorescent lamp is rich in the red and far red light energy needed to provide true coloring in the blooms. The incandescent light bulb produces light that contains red and far-red rays.
Either a cool–white, a warm-white fluorescent, or an incandescent will grow miniature roses. But in order to achieve the true colors in the bloom, a combination of both should be used. Alternate a cool-white with a warm-white fluorescent lamp, or a cool-white fluorescent lamp with an incandescent light bulb at a ratio of 3 watts fluorescent to 1 watt incandescent. Incandescent light bulbs should face inwards; they are easily attached to the ends of a lighting fixture using spring type clamps.
Next to light, indoor temperature is the most important item affecting rose growth. The night temperature should be in the low to mid 60’s, and the day temperature in the low 70’s. The warmer temperature during the day helps the plant manufacture food. The cooler night temperature slows the plant down, so it can utilize this food.
Humidity is the amount of moisture in the air. The recommended humidity for miniature roses is 50 to 55%. In winter the indoor humidity in the average home is often below 15 to 20% unless a humidifier is used. The level of humidity must be raised by placing the plants on trays filled with moist pebbles, or by placing containers filled with water between the pots. Misting the plants a couple of times a day also helps maintain a high humidity. The finer the mist is, the more thorough the coverage. A too low humidity can cause foliage to curl and buds to dry out and drop. It is also one of the causes for leaves turning yellow.
Ventilation is the circulation of fresh air. The leaves of plants continuously transpire moisture. Without sufficient air movement, the moisture condenses on the leaves, creating an ideal condition for the development of fungal disease. Ventilation is also the means by which carbon dioxide is supplied to the plant. The leaves breathe in carbon dioxide during the light hours, and exhale oxygen during the dark hours. Using a small fan helps the air keep circulating between the plants.
When growing roses under lights, darkness is often taken for granted. Darkness is that period when the plant uses the food it manufactured during the light period. It is of utmost importance that you allow the plants to have a period of darkness. Studies have shown that it is not the light intensity or temperature that produces flowering, but the successive rhythmic periods of darkness and light.
MICROCLIMATE: “WINTER GROWTH CHART”
Lamp Distance Temp. Humidity Intensity (f.c)
12 inches 0°F 0 % 500
6 inches 69°F 47 % 860
5 inches 71°F 48 % 980
4 inches 73°F 49 % 1100
3 inches 75°F 50 % 1220
2 inches 77°F 51 % 1340
1 inches 79°F 52 % 1460
0 inches 81°F 53 % 1580
IDEAL CONDITIONS: LIGHT-HUMIDITY-TEMP
Light Hours: 14-16 Hrs/Day Temp. Low-Mid 70’s Dark Hours: 8-10 Hrs/Day Temp. Low-Mid 60’s
The chart above shows actual readings recorded in my indoor light bed.
- By decreasing the distance between lamps and foliage you will increase light intensity and at the same time raise the temperature and humidity in proportion.
- The higher the light intensity, the more heat a plant can endure.
- With a high temperature reading you should also create a high humidity to off-set the moisture lost by evaporation due to the heat.
- With the humidity being on the high side, conditions are right and mildew can develop.
- But at the same time, this moisture will discourage spider mites.
- Providing fresh air and proper ventilation should alleviate the problem.
- If there is a high temperature reading and low humidity, leaves may have brown edges.
There are many factors that determine the frequency of watering. Porosity, soil type, light, temperature, humidity, and the type of container, etc. will determine this. When the soil is starting to dry out, check 3/4″ to 1″ into the soil. If it feels and looks dry, it needs water. Water until it runs out of the drainage holes. Potting soil should be kept evenly moist, never soggy, as this prevents the outside fresh air from penetrating into the root zone.
POTTING SOIL The first requirement is that the soil is sterilized, porous, does not pack, have good drainage, and yet be able to retain some of the nutrients. I use a soil-less potting mix. There are many good ones on the market. Pro-mix, Jiffy-mix, etc., all have basically the same ingredients; peat moss, perlite and vermiculite, only in various proportions. For those just starting out, it may be advisable to use a commercial mix. My own formula for a soil-less potting mix is (1 unit equals 24 cups): 5 units peat moss, 2 units vermiculite, 2 units perlite, 1 unit kitty litter (this is clay), 1 cup Osmocote 14-14-14, ••• cup hydrated lime and 4 Tbsps. Captan 50% w.p., thoroughly mixed.
FERTILIZER When using a commercial soil-less potting mix, you can scratch in a time-release fertilizer as directed for a 6″ pot (if this is the size pot you are using). I use Osmocote 14-14-14. This will feed the soil until spring when the pots are moved and roses are planted outdoors.
There they will be fertilized with the rest of the roses for summer growth. In addition, once a week I use ¼ Tbsp. fish emulsion in a mixture of warm water, combined with a mixture of Captan 50% w.p. (1 Tbsp. Per gal.)
INDOOR PESTS AND DISEASES
Any insect or disease that a plant has to contend with outdoors can also attack the plant indoors. Just as your indoor light table is ideal for growing roses, it is also ideal for insects (a warm, stable temperature, and an environment that is free of nature’s predators that kept them under control outdoors).
Spider mites and aphids are the insects most likely to be troublesome indoors. With plants being in close proximity to each other, insects spread very quickly. A strong spray of water daily will keep the plants free of mites, breaking up their webs and knocking them of the foliage. For a severe infection, dip the plants, stem and foliage, in a solution of Mavrik (use a bucket and submerge the entire plant). For aphid control, spray with water, or a liquid soap and water solution, but flush off the soap the next day to prevent clogging the leaf pores. You can also dip the stem and foliage in an Orthene solution.
Black spot and powdery mildew are the diseases most likely to be a problem indoors (as they are outdoors). I use an Orthenex Formula III solution, dipping the stem and foliage every seven to ten days. This seems to do the job of providing a protective coating on the foliage and at the same time keeping the insects in check without having to resort to any other chemicals.
No spraying of any chemical indoors, never ever. Always wear safety glasses whenever handling any type of chemicals. It should also be pointed out that you must use rubber gloves when you are immersing the plant in any of these chemical solutions. Some pesticides are systemic, and will be absorbed by the skin just as they are absorbed into the tissues of the plant. I am pretty sure the chemicals listed in this article are available and safe to use; always read the label directions and check to be sure. Use gloves, even when using the so-called “safe” insecticides. The poison in some of these chemicals can affect your nervous system, including the brain.
I hope you will experiment with growing roses indoors and enjoy the results as much as I have. Grow only the number of roses as you are able to take care. When it begins to be a chore, it is no longer fun.
Excerpts from: An article I had published in one of the original issues of the Miniature Rose Growers Bulletin in the 1980′s. While the article is several years old, the information is still applicable and may provide some help in growing roses indoors. Over the years I have grown many roses under lights. The procedure is simple and pretty much the same for HT’s, Floribundas, Shrubs, etc.
To download the pdf version of this article click here.