Many factors can cause flowers to change color

By Sherry Fuller

Your long-stemmed, red rose bush suddenly starts producing small, pink flowers. The spectacular bed of purple and pink columbines you planted five years ago now has only yellow and white flowers. The blue, yellow and rust iris you transplanted from a friendís yard are all blooming white. Whatís going on?

Plantsí flower colors can change. There are six easy reasons why this might happen and botanists may discover other reasons as they learn more about how plants work.

Rootstocks

Many plants including roses, fruit trees, shade trees and some shrubs are grafted onto the roots of hardier relatives. This technique can make plants grow faster, stay more dwarf or have other desirable characteristics. The problem arises when the top, grafted part dies, leaving the tougher rootstock alive and ready to grow.

This is especially common in our area with roses. The top dies during the winter and in the spring the rootstock starts to grow, producing few or no flowers and certainly not the long-stemmed beauties you expected from your rose.

If this has happened to your plants, there is no solution other than removing the offending rootstock and starting over. Mulch your grafted roses well over the graft during winter to keep some of the intended plant alive in case of severe weather. And water your roses monthly if we have a dry winter. Winter drought is the main reason roses die here.

Seedlings

Some perennials live longer than we do, others die out after 3 or 4 years. These short-lived varieties often produce lots of seed and the plants resulting from this seed are usually more vigorous than their older parents. If the parent plants were hybrids, as many common garden plants are these days, seedlings from their seed will often not have the same color flowers. Columbines are notorious for dying out after a few years, leaving behind white or yellow-flowered progeny in their place.

Stress

If iris are moved from one place to another and left out of the ground for too long, this stress can result in white flowers. Iris growers I consulted verified this phenomenon, but didnít know exactly why it occurs. Sometimes the original flower color will return, sometimes the plants will bloom another color after a year or two. All the brightly colored iris I moved from one home to another had white flowers the first year, and mostly blue the second. Iím waiting to see what happens next year. Stress may alter the color of other flower varieties as well, but iris are the ones it happens to most frequently.

Iris are tough plants and are often available for sale from corms that look quite shriveled with brown leaves, but that grow with no apparent problem. Soak these starts in water for several hours for best results.

AGE

Tulip flowers tend to turn yellow or white as the bulbs get older. Gladioli tend to turn yellow. Again bulb growers confirm this occurrence, but donít have a good explanation for why. This color-change phenomenon is one of the reasons older bulbs are discarded and younger ones replanted when bulbs are dug and divided.

SOIL

Many gardeners are familiar with hydrangeas that change flower color from pink to blue depending on their soilís acidity or alkalinity. The variety that does this quick-change act is commonly grown in the east, but can be grown here only as a house plant. Acidic soil with aluminum turns these flowers blue, more alkaline soil with iron produces pink flowers. Iím not aware of other flowers affected to this extent by soil, but it is certainly possible.

SPORTS

Weíre not talking football here. A sport in the horticulture world is a plant branch that has noticeably changed, whether it be flower color, leaf color or another feature. Again, no one is exactly sure why, and these are relatively rare in the plant world, but many new varieties come from spontaneous sports. If you discover one in your yard, it must be propagated by cuttings to keep its unique color or form.

We may not always appreciate Mother Nature tinkering with the color schemes in our yards, but itís just a part of growing plants. My solution is just to love the white columbines and blue iris Iíve ended up with.

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