While shovelling out from a heavy snowfall this week, I noticed a rose shrub with reddening leaf buds along its bare canes. This is a sure sign of approaching spring! Plant hormones are stirring, and will soon cause buds to swell and sprout. This is a good time to walk around the garden and check for changes in buds on other woody plants. Some like forsythia and quince are probably advanced enough to cut for forcing into bloom indoors.
Woody plants manufacture their own growth hormones in response to temperature changes in late winter, and that’s why the rose canes have reddening leaf buds. Plant hormones are sometimes referred to as growth regulators in commercial greenhouse production, and as growth factors in commercial agriculture. There are several hormone categories — auxins, gibberellins, cytokinins, abscisic acid, naphthaleneacetic acid, ethylene and polyamines — and each category has multiple hormone elements (for example, there are 100 gibberellins). We don’t really need to know all these chemicals, although gardeners do come across them when using seed germination stimulants (gibberillins) and powdered rooting hormone and transplant solution (indole butyric acid), and when purchasing tomatoes, strawberries or bananas that have been ripened with ethylene gas.
It’s reassuring to know that plants produce their own growth hormones at the appropriate time and in the right amounts. But when putting in new plants in spring, I always feel an urge to dose them with something that will influence stronger and quicker growth. Yes, there’s a small voice telling me I could let the plants develop at their own pace. But my enthusiasm for foliage and flowers in a short growing season is a strong incentive for me to provide a mild transplant fertilizer solution combined with rooting hormones.
Garden centres often have a display of liquid transplant solution under their own label near the checkout counter. Most often it’s a 5-10-5 fertilizer combined with indole butyric acid. Another liquid transplant solution that contains 5-10-5 fertilizer and two hormones, indole butyric acid and napthalene acetic acid, is called Root Booster (veseys.com). Rooting fertilizers in water-soluble granular form may have an analysis of 10-52-10 with no hormone content, relying instead on a large amount of phosphorus (the middle number) to stimulate root growth.
Commercial transplant solutions are easy to dilute with water, and deliver with a watering can. I soak the plants in their pots with the solution, and then water them into their holes with additional solution. After a month in the ground, I give them another drink of transplant solution, watering it into the root zone. New plants experience a period of transplant shock when first set into their holes. Sensing a change in soil temperature and reacting to root disturbance in the planting process, they may wait up to six weeks before tentatively putting out new roots. Using transplant solution eliminates the shock and waiting period, encouraging transplants to begin root growth immediately. That can make quite a difference in plant performance the first season, and speeds up the establishment process.
It’s also possible to deliver spring root-boosting therapy to plants already established in the garden, particularly if they’ve been slow to grow or are recovering from loss of wood through physical damage. I’ve given transplant solution to established cedar shrubs that suffered damage from heavy snow and ice. Keeping in mind that twig and foliage development must be preceded by root growth, mild fertilizer combined with rooting hormones is a good therapy for physical damage to woody plants. Transplant solution will also encourage root expansion on clumps of favourite perennials.
The important key to using hormones for new transplants, as well as for established shrubs or perennials already in the garden, is to follow their natural biological timetable of growth. Supply hormones in spring through early summer when plants are eager to expand their root systems. For later transplanting and feedings in midsummer, supply fertilizer alone. When dividing plants in late summer and early autumn, set divisions into their holes with just water, or use an organic fertilizer like compost or aged manure.