Tag Archives: silver leaves on rhododendrons

The October Garden

The glory of the sino nuttallii rhododendrons

The glory of the sino nuttallii rhododendrons

Floral Legacy in bud

Floral Legacy in bud

Rhododendons may no longer be the elite fashion item they were for so many decades, but we still love them.

When we started in the plant business back in the early 80s, rhododendrons were a hot ticket item. We were but one of several rhododendron nurseries in Taranaki and to survive, we needed to find our own niche. To this end, we grew a different range, specialising in varieties that would perform well in warmer climates – like Auckland. After all, even back then, one in four New Zealanders lived in greater Auckland and we figured that if we were going to sell them rhododendrons, we might as well sell them ones that would do better for them. Mark’s father just happened to have done some breeding to find varieties that were more resistant to thrips, didn’t get that burned and crispy edging to their foliage and were predominantly fragrant as well as floriferous. It gave us a good place to start.

Nowadays there are no specialist rhododendron growers in Taranaki at all and the demand has melted away. I no longer have to try and convince people that not all rhododendrons have a big full truss in the shape of a ball but many have loose trumpets in curtains of bloom instead.

Rhododendrons are one of the backbones of our garden and we wouldn’t have it any other way. While they have a relatively short season in full bloom, the anticipation of fattening buds stretches out the weeks with the promise of delights to come. They are as fine a shrub as any we grow here and a great deal more spectacular than most.

The nuttalliis! Oh the nuttalliis!

The nuttalliis! Oh the nuttalliis!

The nuttalliis. Oh the nuttalliis. Peak nuttallii season doesn’t start until closer to the end of the month, taking us into November but some varieties have already done their dash for this year. If we could grow only one type of rhododendron, we’d choose a nuttallii and even more specifically, the sino nuttallii from China. You can keep your big red rhodos (most people’s favourite pick). We love the fragrant, long, white trumpets which look as if they are made from waxed fabric, the lovely peeling bark and the heavy textured foliage. These are rarely offered commercially now so grab one if you ever find it for sale.

Thrips!

Thrips!

It is, by the way, nasty little leaf-sucking thrips that turn foliage silver and no, you can never turn those silver leaves green again. If you look at the underside of the leaf, you can see dark thread-like marks – these are the critters that do the damage. All you can do is to try and prevent the new season’s growth from getting similarly infested. We are not at all keen on spraying insecticide these days and you need a systemic insecticide that the plant absorbs into its system to get a thorough kill. If you must go down this path, spray in mid November, early January and late February for maximum effect. Others praise Neem oil instead but we haven’t tried it.

We favour choosing more thrip-resistant varieties, keeping them growing strongly and opening up around them to let more air and light in. Thrips prefer shade and shelter. Unless it is really
special, if it is badly thrip-prone, we replace it with a better variety. Not every plant is precious.

In the longer term, plants come and go in the fashion stakes. Goodness, even red hot pokers are having a resurgence of popularity. We don’t worry about the fashion status of the rhododendron and Mark continues hybridising for better performing cultivars. If there is no commercial market for the results, it doesn’t matter. We will continue to enjoy them in our own garden.

First published in the New Zealand Gardener and reprinted here with their permission.

Rhododendron Barbara Jury - one of Felix's hybrids

Rhododendron Barbara Jury – one of Felix’s hybrids

Outdoor Classroom – Rhododendrons: common problems and solutions

1) Silver leaves. By far the most common problem is thrips sucking the chlorophyll out of the leaves, turning them silver and weakening the plant. Turn the leaf over and you may find black, thread-like insects on the back. Replace heavily infested plants – some varieties are more susceptible than others. Open up around the plant for more air movement and light. You can use a systemic insecticide – spray November, early January and, for really bad cases, late February. Neem oil is recommended by some as an alternative to insecticides.

2) Leaves with dry brown patches and edges. This is usually a sign of stress. The plant may be too dry or too hot. Move it if necessary (sun for half the day or dappled light is best) and get a blanket of mulch over the roots. Some varieties prefer a much colder winter than we have and these tend to burn and crisp on the leaves. Replace them. Some plants get touched by mildew and lichen. Open up to allow more air movement.

3) No flower buds. This is usually a sign of too much shade. Move the plant or open up around it to allow more light.

4) Leggy, bare and stretched. Again, this is usually a sign of too much shade. Some varieties have a tendency to get rangy and open, others are naturally more compact and bushy. You can rejuvenate a leggy plant by cutting back very hard but it is really too late in the season now. It is best done in the middle of winter. You are more likely to kill the plant if you cut it back to bare wood now. This plant was cut back hard two months ago and has made its new growth already.

5) Plants which make only one new growth from each stem can be encouraged to make several growths by pinching out the single shoot. Do this as early as you can or you will be pinching out next year’s flower buds. In the right hand photo, you can see a plant making several new shoots instead of only one.

6) If not deadheaded, some rhododendrons set so much seed that it can weaken and even kill them. It can also reduce flowering the next season. This plant missed being deadheaded last year. Varieties that don’t set seed are generally deadheaded for aesthetic reasons, not because it is necessary.

In the garden 01/01/2010

  • If you are making only one New Year’s gardening resolution, for long term gains resolve not to let weeds go to seed. Long term it is labour saving. The light rains this week will have given enough moisture to start the next round germinating. Get them early with the push hoe. If you have ignored the last round and they are setting seed now, weed with a bucket at your side or you will be spreading the seed. Unless your compost heap generates high temperatures (and the black plastic types rot the contents, rather than sterilising by heat), keep seed heads out of the compost. You can either put them out in the rubbish (hopefully they get buried so deep in landfill that they can not germinate there) or if you don’t have rubbish collection, putting them in a black plastic rubbish bag in full sun should work.
  • Do not delay on dividing the autumn flowering bulbs which will be triggered into growth soon. These include nerines, belladonnas, colchicums (often called the autumn crocus), most ornamental oxalis and cyclamen hederafolium. The rejuvenated clumps will reward you soon enough.
  • Flowering cherries are summer pruned to avoid the effect of silver blight. If you have a tree with witches broom, you will have noticed in spring that you had sections which did not flower and where the foliage was much denser and came while the rest of the tree was flowering. Cut out the witches broom before it takes over the entire tree (which it will over time) because then you will have to cut out everything.
  • If you had a problem with silver leaves on rhododendrons last year, check for fresh infestations now by looking underneath the leaves. The problem is leaf sucking thrips. The adult thrips are black and thread-like while the youthful offspring are white. The usual approach is to blast them with a systemic insecticide which the plant sucks into its circulation system. If you are not at all keen on this approach, cut out weak and badly infested plants (the damage won’t be showing in the new leaves yet but it will happen), and open up around other plants to increase air movement. Theoretically, an oil spray will suffocate the little critters and you can use a mix of light cooking oil with a squirt of detergent mixed with warm water. However, the problem is that you have to spray directly onto the underside of all leaves because it will only suffocate on contact so this is only practical where you have a very small number of plants. We haven’t tried them but apparently the collars of insecticide wrapped around the trunk can work well. The DIY approach is to secure a band of carpet around the trunk and then inject the concentrated systemic insecticide into the carpet. Wear gloves.
  • Garlic can be harvested when you think it has reached a good size. Lift it and leave it on the ground while the foliage dies off. After being given a large bulb of smoked garlic at Christmas, we are keen to try smoking some of this year’s crop to see if it extends its shelf life through the season. Garlic tends to lose its oomph after about six months. The smoked garlic is wonderful for aioli and summer dressings.
  • Unlike garlic, you have to wait for the tops of onions to bend over and start to wither before lifting the crop.
  • Keep successional sowings of sweet corn, lettuce, salad veg and beans going and in a warm spot, you can plant a late crop of tomatoes.

November 13, 2009 In the Garden

  • We are starting to dry out already. Keep a close eye on container plants. If they are showing signs of stress, it is likely they are either badly root bound (should have been potted on when we told you in winter), hungry or dried out. To get water back into dehydrated plants, a squirt of dishwashing detergent or surfactant will help absorption. However, ignore any advice given elsewhere to add water holding crystals (also called Crystal Rain) to potting mix for anything other than annuals. In our climate with high rainfall, woody plants and perennials will rot out in winter if you add these crystals, however tempting it may be in summer to use them. Partially burying pots and containers into the garden (called plunging) can reduce excessive drying out. It also stops pots with taller plants from blowing over in the wind.
  • It is late in the season for planting out woody trees and shrubs, especially if they are large or root bound. Our advice is to heel them into the vegetable garden until autumn. If you are determined to plant into other garden positions, make sure that the root ball is soaked right through. A watering can just will not do. It can take hours (or leave overnight) to get the water into the middle if it is very dry. Once planted, mulch to conserve moisture and keep an eye on the plant until Christmas at least to ensure that it has not dried out again.
  • If you spray for thrips on rhododendrons (the leaf sucking critters which cause silver leaves), get the first application on when you see the insects on the under side of the new growth. We are not keen on this practice and will only spray one or two special plants ourselves. We would be much happier to hear of gardeners opening up around the plant to encourage air movement, feeding and mulching to encourage more health and vigour and taking out plants which are particularly susceptible to replace with healthier selections. We have drawn a line under many of the cold loving German and American hybrids here and said that we just can not grow them well in our mild, coastal conditions.
  • It is the optimum time for planting kumara runners. This is one plant which really loves warm, light soils.
  • As soon as we get more rain, fungi are likely to attack potatoes and tomatoes. A copper spray applied as soon as the foliage has dried out after rain is usually necessary if you wish to guarantee a harvest later.
  • Brassicas will be under siege shortly, if not already, from much of the insect population and in particular the dreaded cabbage white. This is the single biggest reason for not growing brassicas for summer harvest in our climate. If you don’t wish to spray with an insecticide, you have to start getting creative with old net curtains and the likes. However, this only stops the cabbage white laying more eggs and does nothing to deal to existing caterpillars in residence. We will be eating our remaining brassicas soon and not replanting until autumn, with the exception of brussel sprouts which are best sown in the summer for harvest next winter.
  • Leeks can be sown now.