An Ivy Green Thumb
Dr. Charles W. Dunham
Professor Emeritus, University of Delaware
Developing an ivy green thumb is no more than careful observation of your plants and learning to interpret their responses. Growing ivy, as growing any plant, involves an understanding of plant requirements and devising a strategy to provide them. Each species of plant needs light, air, water, nutrients, and suitable temperature in order to survive and grow. The conditions needed by all plants are more similar than dissimilar, but the exact combination of factors varies somewhat for each species, and when one variable in the environment is changed it may require changes in others. Light and temperature interact to influence plant growth and in turn determine the requirements for water and nutrients. Each soil or soil mixture has properties (influenced by watering and fertilizer practices and pot size and kind) that affect the ability of the plant roots to obtain air, water, and nutrients. Fortunately, ivy is able to grow and thrive over a wide range of conditions, which is why it is such an excellent plant both in the house and outdoors.
LIGHT and TEMPERATURE
Light intensity and temperature are critical factors for growth of all plants. In the house, light intensity varies according to the season of the year and the exposure. Light intensity is low in winter months and increases in summer. North windows receive indirect light and the intensity is always less than an east, west, or a south window, which is generally the highest. Ivy is quite tolerant and will thrive in any of the windows with direct exposure. Ivy can exist for some time and be quite attractive in a dark corner of a room. However, it will grow very slowly and need much less water and nutrients in this situation. Stimulation of growth in such an environment by excessive amounts of water and fertilizer will result in thin spindly pale growth. In a sunny window ivy will grow much more vigorously, have bigger more attractive leaves, and its requirements for both water and nutrients will be greater.
Ivy can grow and survive over a wide range of temperatures. Some species and cultivars are quite frost hardy out of doors while others do well indoors at temperatures comfortable for people. When ivy is brought indoors for the winter and is kept under conditions of low light, it will do best if temperatures are also low, and water and nutrients are applied sparingly to keep growth at a minimum.
When ivy is kept in rooms where there is no window available, additional light can be supplied by placing them near floor lamps. Ivies thrive under light trays like the ones used for African violets.
Out of doors ivy will grow in both sunny and shady exposures, but perhaps does best in a north facing site where it is protected from winter sun.
Learning to water is one of the most important skills in plant care. Too much water and plant roots suffocate and die; too little water causes growth to become erratic and stunted. The question, "How often shall I water?", will depend on the conditions under which the plants are growing. For ivy, it is best to water so a little drains out the bottom of the pot and the whole soil ball is wet, then allow the plant to dry out almost to the point of stress before watering again. The time between waterings will depend on: the time of the year, (amount of light and temperature), the size of the plant and its root system in relation to the size of the pot, the type of soil, the kind of pot (clay pots dry out faster than plastic or ceramic pots). The interval between waterings may vary from every day or two, to as much as a week or more. Learn to look at the soil, feel the soil, lift the pot to determine how dry the soil is. Some plants start to visibly wilt when dry, but when ivies wilt it is too late. Pots that do not have drainage holes require extra care so that they are not over-watered.
POTTING SOILS AND POTS
Ask gardeners about the soils they use for a particular plant and you may get as many answers as there are gardeners, which means there is no magic soil-mix, only gardeners who know how to manage the soils that they have.
The synthetic soiless mixes have found wide favor among commercial growers of ivy and can be used by home gardeners. The mixes are especially good for rooting and growing small plants. There are a number of brands available in garden stores.
A good potting mix can be made from available garden soil. Use good garden loam and mix roughly equal parts of loam, sphagnum peat moss, and coarse sand or horticultral perlite. Adjust the amount of soil and sand to give a final mixture that drains quickly when the pot is watered. To a bushel of soil mix (32 quarts) add 1 cup of dolomitic lime and 2 cups of bonemeal. Be sure to mix all ingredients thoroughly.
The question of clay versus plastic pots is one of practicality. Because of cost and convenience, commercial growers use plastic pots and synthetic soil mixes almost exclusively. Clay pots and a potting mix containing some soil is my preference for plants grown indoors and as specimens, Ivy runners can be grown in water. They really do not grow well because of the lack of nutrients, but they will form roots and survive for an indefinite time. Transplanting these plants to soil requires care. Pot in perlite and place the pot in a pan of water so that the water comes about half way up the pot. Let the water level drop gradually over a period of a week or two. Then it can be potted in your potting mix (soiless mixes are great here), and normal watering can usually be started, along with a very dilute applications of fertilizer.
Sixteen or more mineral nutrients in varying amounts are required by plants for normal growth. Plants obtain nutrients from the soil and soil solution through the plant roots.
The nutrients most likely to be lacking in sufficient amounts in most soils are nitrogen, phosphorous, and potassium. The percentages of these three nutrients are stated on all commercial fertilizer packages and abbreviated NPK, always in the that order. For example, a 15-15-15 fertilizer comntains equal amannts (15%) of nitrogen, phosphorous and potassium.
In addition to these three nutrients, some fertilizers may contain required nutrients like magnesium, sulfur and others in very small amounts like iron, manganese, and boron. These additional nutrients become increasingly important when synthetic soil mixes are used.
Brands of fertilizer may differ not only in the amount of nutrients they contain but in the way the fertilizer is formulated. Most commonly, nutrients will be present as mineral salts. In most house plant fertilizers these will be completely soluble or in liquid form, while garden fertilizers will have insoluble fillers like sand added. Other formulations may contain the nutrient elements in organic compounds (fish emulsion, organic fertilizer, bone-meal) that need soil microbes to break them down and convert them to soluble mineral forms that can be absorbed by the plant roots. One type of fertilizer has the soluble nutrients encased in a plastic shell that allows the fertilizer to slowly seep out when in contact with moisture (Osmocote). Of course it will need to be applied much less frequently. Directions are given on the label.
The exact requirements and best formulation for ivy is not known and probably doesn't exist, at least for all situations. It is generally believed that ivy needs as much nitrogen as phosphorous and potasium (15-15-15). An excellent system is to use a soluble mineral fertilizer dissolved in water and applied bi-weekly or monthly; fertilize during times of active growth.
Granular garden fertilizers and formulations like Osmocote can be sprinkled on the soil in the tops of the pots and will release their nutrients when the plants are watered. Most brands of fertilizer can be expected to work reasonably well. However, don't be afraid to experiment as different brands and rates may work better in your particular situation. With all fertilizers, too much of a good thing can have serious consequences. Always start out by following guidelines provided for each brand. Remember, young plants and newly rooted cuttings require and tolerate much less fertilizer than older established plants. Plants need less fertilizer when other factors such as light, temperature, or water limit growth.
Fertilizers tend to accumulate in all pots and should be removed periodically by leaching. Do this twice a year, take your plants to the sink and immerse them in water to the top of the pot. Allow them to sit for fifteen minutes then lift them out and let them drain.
This is also a good time to prune and shape your plants and to wash the leaves, which is a good preventative measure for plant pests. If any aphids, spider mites or mealy bugs are found, in addition to washing the leaves, plants should be treated with light-weight horticultural oil either by spraying or dipping the plants.
Increasing water, light, nutrients and temperature will usually increase the rate of growth and size of the leaves. However, best leaf color and plant form is usually attained with conditions that produce somewhat less than the most rapid growth. With common sense, close observation, and regular care, you can learn to manipulate and balance the factors that control the growth of your ivies, and you will be amazed at how easy it is to have an ivy green thumb.