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HOUSEPLANTS |
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KEY CONCEPTS
II. Acclimatization of New Plants
- Greenhouse conditions vs. home conditions
- Maintenance vs. growth
- Acclimatizing houseplants to the outdoors
- Potting and repotting
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ACCLIMATIZATION OF NEW PLANTS
GREENHOUSE CONDITIONS VS HOME CONDITIONS
Commercial growers strive to maintain optimal growing conditions. Light, temperature and humidity are controlled by specialized equipment and trained staff. It is unlikely that these conditions can be duplicated in the home. Central heating systems make home humidity lower than greenhouse conditions. Light is usually drastically lower in quality and quantity.
Houseplants should be gradually weaned from the near-perfect conditions of the greenhouse before being placed in the home. This is called acclimatization. Scientific study has shown that plants produce both sun leaves and shade leaves. Plants grown in the sun have thicker, smaller, more numerous leaves. These leaves have less chlorophyll. Shade leaves are thinner, larger and fewer. They contain more chlorophyll. When light conditions are dramatically changed, leaves must be replaced. A gradual change through acclimatization is less stressful to the plant.
When newly purchased plants are brought home, first place them in a south-facing window or high light area. Then gradually, over 4 to 8 weeks, move them to the darker location. This will give plants time to produce the right leaves for the light in the new location, assuming the light level is adequate for the plant.
The best time to buy new plants is spring through early autumn, when conditions in the home are adequate for growth. In winter, the home environment is dry from heating, and the quality and amount of light are reduced. When making plant choices, remember that younger plants will acclimatize more easily to home conditions than mature plants.
Protect newly purchased plants to prevent exposure to sudden temperature changes during the move from the store to the home. During winter months, cover plants with plastic or paper bags or wrap them in newspaper. Cardboard boxes will offer further protection during the ride home. Consider the length of the trip. The trunk of the car is too cold to carry plants home safely in winter. Most foliage plants will be damaged if exposed to temperatures below 50 degrees F.
In summer, avoid keeping plants in the car for long periods of time. Temperatures rise very quickly, which may result in rapid loss of moisture. Shade plants from direct sun while in the car. Do this even though the air conditioner has cooled the air temperature.
When considering how to care for houseplants, it is important to decide if growth is desired. It is usually easier to maintain a plant in the home rather than have it grow in size. Plants have varying growth rates. Younger plants grow faster than older plants.
Growth rate varies with factors in the environment. Plants have seasonal growth fluctuations. In the spring, as days lengthen and intensity of light increases, houseplants grow quickly. As the days begin to shorten in late summer, growth gradually slows. During winter, most houseplants do not grow. Maintaining houseplants in a healthy condition should be the goal for the winter months.
The purpose of a plant will determine whether growth in size is desired or maintenance is the goal. To maintain a plant at the same size, the home gardener must manipulate factors in the plant's environment. Care must be taken not to stress a plant with extremely low light and fertilizer levels.
Plants that are maintained are usually fertilized less than those that are expected to grow. Pruning will help control size. Both above-ground parts and roots can be pruned to maintain plant vigor, but keep size constant. If a plant is maintained at the same size and in the same sized container, it should have its soil renewed annually. ROOT PRUNING or slicing off the bottom and sides of the outer root ball is done to allow room for new root growth. Remove no more than one half the root ball. Root pruning allows the plant to continue its growth but not outgrow its container.
You may not be able to repot larger plants. Instead, the top few inches of soil should be removed and renewed.
ACCLIMATIZING HOUSEPLANTS TO THE OUTDOORS
Many people put their houseplants outside for the summer. This provides ideal growing conditions for many of the tropical and subtropical plants. It is important to acclimatize
the plant to the outside conditions by gradually increasing the intensity of light. Move the plant first to a shaded porch or under a large tree for two weeks. Then move the plant to a partially shaded area. Finally, move it into the sun, assuming it will tolerate full sun.
The plant may be kept in its own pot or removed and placed in the soil. Growth will be more dramatic in well-prepared garden soil. However, repotting at the end of the season will damage roots and have a higher potential for introducing insects. To move plants back indoors, simply reverse the process. Pay special attention to insects that have infested the plant while outdoors.
Potting and repotting of houseplants should be done for various reasons. Plants will outgrow their container and become pot-bound. The soil should be replaced if there is a salt buildup or if soil becomes compacted. The owner may wish a more attractive container. Remember, a few plants, such as clivia, thrive under pot-bound conditions.
In a garden, plant roots are free to spread throughout the soil. Indoor plants are restricted to a smaller area that can quickly fill with roots. Sometimes it is not obvious that a plant has outgrown its container. Plants should be periodically removed from their container to examine the roots. Over time, the soil in any pot loses organic matter. Nutrients are leached out by watering.
Roots can be examined by loosening the plant from the container. Water the soil before examination. Give a gentle tap on the rim of the pot to loosen the plant. If there are mostly roots and little soil, the plant is pot-bound and it is time to repot. Roots growing out of the bottom of the pot is another sign that the plant is pot-bound.
Repotting should be done in spring, when the plant begins active growth. If the repotting of a flowering variety is being considered, wait until after it has flowered.
The next pot a plant goes into should be no more than two inches larger in diameter than the current outgrown pot. If a very small plant is being repotted, the difference in pot size should be 3/4 to 1 inch between old and new. A small plant should never be potted in a large pot. If this is done, water is retained in the soil because roots are not absorbing the water. Under these conditions, the soil can remain waterlogged, creating ANAEROBIC conditions.
The steps to repotting are demonstrated by illustrations. First, the plant must be removed from its existing container.
[diagram]
Be sure to moisten fresh potting media. This makes it easier to use. It should be wet enough to form a ball, but able to fall apart when poked or squeezed. Drainage material (stone, broken piece of pottery) is not needed in the bottom of the new pot because a pot with drainage holes should always be used. Scientific study has proven that drainage materials at the bottom of a container give no advantage. They merely reduce the amount of soil that can be put into the pot. Screening material should be placed over the holes so soil does not flow out the holes.
If the plant is pot-bound, cut and loosen the roots. Remove and replace the top inch of soil if salt buildup is noticed. Position the root ball so that the original soil level is maintained. Fill in soil around the sides. Do not add soil above the original level on the root ball unless roots are exposed or some of the surface soil had to be removed. Allow enough headroom so an inch or two of water can be applied.
Do not pack the new soil. Instead, settle it by tapping the pot against a flat surface. The first watering will cause soil to settle. Additional soil may need to be added.
There should be enough space to allow for applying enough water to thoroughly moistens the soil
Houseplant containers are made from plastic, clay, ceramics, fiberglass, wood, and various metals. Containers should be large enough to allow proper watering, have drainage holes, be clean, and coordinate well with the plant. Do not use pots or containers that do not have drainage holes. If there is no drainage opening, roots will sit in water, and soil pore space will be filled with water. Drainage is a must if houseplants are to thrive.
Unglazed clay pots absorb and lose moisture through their walls. Moisture and nutrients accumulate in the pores of clay pots. Therefore, plant roots tend to accumulate next to the walls of these pots. Unglazed clay pots provide excellent AERATION for plant roots. New clay pots should be soaked in water for a few hours before potting. Otherwise they may wick out all the moisture from the potting mix. Although clay pots provide excellent aeration, they also dry out most quickly of all container types. This fact will impact frequency of watering.
Glazed ceramic pottery with drainage holes are commonly available. This is not a very porous container type, but it is very decorative. Plastic and fiberglass containers are light, inexpensive and easy to clean for reuse. They are not porous. Glazed ceramic, plastic and fiberglass pots will not accumulate salts as quickly or require watering as frequently as unglazed clay.
Self-watering containers are available. They have built-in water reservoirs. Water travels into the potting medium via a wick. These containers offer the advantage of less frequent watering. However, fertilizer salts are often moved up to the surface with the water, leaving a white toxic crust that must be removed.
Other container options include terrariums, bottle gardens and dish gardens. Instructions for constructing a terrarium are provided in Fact Sheet 1001, Reference House.4.
Houseplant growing conditions are rarely as good as native conditions. It is even more critical that the potting mix be of good quality. It must be porous, yet able to retain water and nutrients.
Most commercial potting mixes are soilless. Soilless mixes have the advantages of being light, easy for roots to penetrate and free of insects and disease. High quality mixes contain slow-release fertilizers that provide nutrients for several months.
Inexpensive potting soils are found in many retail stores. They are often very dark in color because they contain large amounts of organic matter. Problems arise because these mixes compact readily and retain too much moisture. The home gardener can prepare soilless mixes at home. Information on preparation of soilless mixes for houseplants is presented in Fact Sheet 572, Reference House.5.
Potting mixes that contain mineral soil provide larger plants more stability because they are heavier. For larger plants, a potting medium containing soil is best. However, homemade mixes that contain soils have several disadvantages. Finding good quality topsoil is often difficult. Garden soil will contain pathogens and insects. Before using garden soil, it should be pasteurized. A growing mix that contains soil has a tighter structure and less pore space for root growth. It must be amended with equal volumes of organic matter, sand and vermiculite or perlite.
Be aware of the special potting media that should be used with some plants. One group of plants, EPIPHYTES, are grown on pieces of bark or potted in a special mixture that may contain sphagnum moss, bark or plastic chips. Know the proper soil for the specific plant.
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