Garden Docs: Why is my phormium changing color?

Editor’s Note: After more than 20 years advising Sonoma County gardeners on their horticultural problems, the Garden Doctors are retiring. This is their last column and they sign off here, with warm goodbyes to readers.

What’s going on with my phormium?

Edith and Bill N. write: Our garden is good-sized and we chose to plant several varieties of phormium (New Zealand flax), emphasizing their beautiful variations in color. To our dismay, most of them are no longer colorful and some have even changed from smaller varieties to very large plants. Can you shed some light on this problem?

Over the past years, as we learned more about the many popular phormium cultivars and their cultural requirements, we also became aware of their tendency to revert to green or bronze. This is referred to as their color stability. Selecting those cultivars that are known to be more stable and diligently removing new unwanted bronze or green shoots immediately as the new growth appears from the base of the plant will keep the colorful leaf forms that drew you to the plant when you bought it.

Although the task may seem daunting, try to cut out the new offending shoots as close as possible to the ground, at the plant’s base. A pair of sharp, heavy-duty shears will allow you to cut through the tough swordlike leaves more easily.

More tips on phormiums

For many years, San Marcos Growers has specialized in phormium cultivars, with expertise on growing and selecting these large, strap-leafed evergreen perennials. Here are some of their excellent tips:

Hybrid flax are more susceptible to hot and cold temperature extremes. (Hybrid forms are a cross between Phormium cookianum and Phormium tenax.)

Phormium prefer moderate water and soil that drains reasonably well.

If you have heavy soil, plant the flax on a mound or slope.

Fertilize occasionally with phosphorus to keep the leaf colors vibrant.

Know the difference between Phormium tenax (larger coastal flax) that most gardeners are familiar with and Phormium cookianum that is smaller and has a weeping and very graceful form.

Phormium cookianum does best in bright shade, which will prevent scorch burns from hot direct or reflected sun. Coastal cool areas should not experience scorching problems.

Here is a sample of beautiful and “stable” phormium hybrids that are less likely to revert. The mature height listed also will be its mature width. It is always a good idea to take height and width measurements into consideration before planting. Phormium are not always easy to transplant if they are the taller cultivars.

P. cookianum, ‘Cream Delight’: 3 feet, cream-yellow mid-rib stripe and green margins with red

‘Dark Delight’: 3 to 4 feet, with arching dark reddish-brown foliage

‘Dazzler’: 3 feet, deep maroon and scarlet (remove old foliage as needed)

‘Maori Chief’: 6 feet, rose-red margins on leaves

‘Tom Thumb’: 2 feet, green leaves with red-bronze margins

‘Sea Jade’: 4 to 5 feet, upright rich green leaves and maroon to bronze mid-rib stripe

‘Sundowner’: 6 to 8 feet, with upright very wide bronze-green leaves with rose-pink margins fading to a cream color

‘Jester’: 1.5 to 2.5 feet tall with arching leaves that are rich pink with hints of orange edged in lime green

‘Jack Spratt’: 18 inches tall with twisting reddish-brown leaves

Help. My apple tree has scales.

Benjamin asks: I took a sample of an apple twig into a nursery and was told it looked like a scale infestation. My apple tree shows some stress, so how do I control this problem? I certainly don’t want to lose the tree.

The best control of scale insects means understanding their life cycle. San Jose scale feed on the sap of apple, pear, other fruit and shade trees. They appear as small gray circular bumps with a lighter center. Scales cause small reddish spotting on apples and twigs resulting in a mottled appearance.

Scale is in the dormant nymph stage during the winter months. As soon as the sap starts to flow in the spring, the nymphs begin to feed until approximately bloom time. They are then full grown and will fly and mate with stationary females. Eggs are produced and tiny yellow crawlers hatch after petal fall. During this period, you can see them busily moving over the bark searching for a site to settle, feed and do their damage. At this time they secrete a waxy covering that will protect them from insecticides. (More bad news — they produce three to four generations per season.)

Here is a brief spray-timing schedule:

• Spray dormant oil or lime sulfur before spring bud break.

• Crawler treatments are most effective when applied about one month after apples first bloom. A good technique to determine crawler emergence is to regularly shake suspected infested branches over a sheet of dark paper. The newly hatched crawlers will then be easy to detect.

Lastly, infected twigs and branches should be pruned or removed as much as possible.

Encourage birds to frequent your garden since they will feed on scale crawlers. Parasitic wasps are also used for biological control.

Garden doctors say goodbye

As I write this last column and bid farewell to our faithful readers, I wish to say I have enjoyed your questions and researching answers to help you in your gardening endeavors. We explored topics ranging from problems with deer and other critters/varmints, propagation, companion planting, plant disease and insect damage to firescaping, pollinators, landscape design, soil problems and several more subjects of interest. I appreciate the opportunity The Press Democrat has given these past 22 years to provide this educational service to the gardening community. I hope you have enjoyed it as much as I have. Thank you and good luck in your future gardening efforts. — Dana Lozano

It has been both fun and educational answering all your gardening questions for the past 22 years. But it’s time we say farewell and thank you to all those who read and enjoyed our gardening column. — Gwen Kilchherr