Mycorrhiza in the garden

I was probably overly harsh on the subject of Japanese maples and mycorrhiza on Friday. In practice, some benefit can be obtained from mycorrhizal treatment but overall, the difference in growth is going to be marginal, assuming that you have a healthy plant to start with. What mycorrhiza can't do is revive or improve the health of a poorly performing maple. As far as the soil microflora is concerned, boosting bacteria numbers and variety will have a far more impressive effect on the overall well-being of your Japanese maple and this is a subject I'll go into in more detail in a future post.

The reason mycorrhiza have little effect on maples is due to how they originally evolved and the types of plant they developed a symbiotic relationship with. Although it's not immediately apparent, the fine feeding roots of a Japanese maple are covered with a mass of root hairs. If you grow a seed and the initial root hits a small air pocket in the growing medium, the root hairs are easily visible. Under normal growing conditions, if you pull up a maple you won't see anything as the root hairs will be within the soil or are easily pulled off. You can see a more obvious picture of root hairs on something such as a lily bulb, particularly the roots that grow above the bulb from the base of the stem.

Root hairs serve the same purpose as mycorrhiza and specifically arbuscular mycorrhizae, as these are the symbiotic fungi most closely associated with garden plants. The root hairs penetrate the soil and provide the plant with it's nutrients in the same way as mycorrhiza do and no symbiotic relationship is required for the plant to perform 100%.

The root hairs also serve another purpose and that is as a barrier to fungi, good or bad and inoculating the soil will mean the fungal hyphae can't reach the roots and develop within them. This barrier to mycorrhiza is only present in plant species that are relatively 'new' and have developed more sophisticated forms of nutrient uptake. Acer palmatum is a very 'young' species in terms of evolution and is still unstable. This manifests itself in it's inability to produce offspring that look identical to the parent; sow a thousand seeds and you will have the majority of them unique in leaf shape and form. They may all look very similar, either red or green, but there will be subtle differences in shade of colour, the serration on the lobes or leaf size.

Where mycorrhiza can make an appreciable difference, however, is with the more 'primitive plants and I shall, hopefully, cover that tomorrow, as this type of plant is the reason for the existence of mycorrhizae.

Mycorrhiza, nature's root extensions

Looking through all the information I have on mycorrhiza, to put in this post or spread it over several days would produce an impossibly long article. For the moment, the best introduction I can give is to send you to the following site: Introduction to Mycorrhizas

I'll discuss how best to manage mycorrhiza in the garden tomorrow and provide some information for growers of exhibition vegetables.

What not to buy

Following on from yesterday's post, I thought it would be a good idea to illustrate some typical aphid activity. If you click on the picture, I've put two larger versions on my web site. You'll notice they're starting to congregate at the base of the dying leaf stems and around the base of the current season's shoots. These are all ideal hiding places to lay eggs; not to get away from you but to protect the eggs from birds. Again, the same advice as yesterday; kill them before they kill your plant! And yes, small plants can be severely weakened in the spring and can die.

When I'm browsing on the Internet I sometimes suffer from WILF (what was I looking for!) and I ended up on a Technorati page listing that had links to some Youtube videos. I clicked on one of them and it turned out to be a clip from Garden Time tv and an interview and product plug with a garden centre owner describing some Japanese maples. So far, so good, although I never take any notice of people telling me a particular variety is only going to get to a specific height; a good rule of thumb: take the height and double it!

What they were advertising at the end illustrated the danger of jumping on a bandwagon without having the facts to back it up. In essence, they were promoting mycorrhiza as a 'must have' for improving the quality of your Japanese maple. The product contained lots of different strains that would, apparently, all help to make your maple healthier and more vigorous, protect it from soil-borne diseases and generally act as a universal panacea.

The reality, however, is somewhat different. Mycorrhiza have little or no effect on the well-being of your Japanese maple and applying beneficial fungi to them will not be cost effective.

As a professional nurseryman, I started using mycorrhiza in the late nineties when reliable strains first became available, although having said that, there was a lot of rubbish about just as there still is and considerable testing of their effectiveness had to be done. Initially, it held some promise, at least in theory and I started using it extensively but more research and field trials showed that, on it's own, it was doing nothing. There were other elements of the soil microflora that had a far more important role as far as Japanese maples were concerned; specifically, bacteria and some of the most important of these are Azotobacter, Pseudomonas and Rhyzobium.

The subject of soil microflora is an important one, not just for Japanese maples but for most garden plants. I'll come back to this subject next week as there is a large amount of information that can be of great benefit to all gardeners and I'll also have a secret tip for growers of exhibition vegetables that probably no one, outside of a laboratory, is aware of.

Need more information? find it at growing Japanese maples.

Japanese maple pests

Today I took my first inspection through my stock plants to see what wood is going to be available for grafting this winter and was glad I hadn't left it any longer. Although I regularly inspect plants during the summer when aphid populations can build up quite quickly, some had obviously been overlooked. Several trees had infestations of juvenile aphids crawling all over them and action need to be taken fast.

To the casual observer, the sight of aphids in the autumn, whilst acting as a reminder that they need to be removed, won't engender any sense of urgency. It's a job that can be done when you've got some spare time next week or next month, if at all. You're thinking 'the only thing they seem to be doing is putting a sticky deposit on the leaves; they're going to fall off shortly and the upcoming cold weather will kill the aphids off so I'll leave it as I've got more important things to do in the garden'. Big Mistake!

What you can't see unless you get up very close and if you can see, it's too late, is the aphids are laying eggs. Initially, they're walking up and down leaf stalks and shoots, but gradually they will start congregating in specific ares, ready to unleash a time-bomb next spring. They will start laying their eggs in the leaf axils where next year's buds are developing. They're going to be in tiny cracks in the bark next to the buds and in the bud sheaths themselves. Once they've been laid, there is nothing you can do apart from wait for them to hatch next spring.

Unfortunately, next spring is going to be too late to minimise the extensive damage they can cause as, conveniently for them, they hatch just as the buds start expanding. But this time they're not going to be walking all over the leaf surface, at least not initially; they're going to be within the expanding buds. But it gets worse! They're not interested in the fully opened leaves where it's easy to get at them; they're going to be feasting om the most succulent part of the shoot, the growing tip and all you'll see is a mass of sticky distorted shoot tips covering the whole of your Japanese maple and severely weakening the growth of your plant.

When it gets to this stage, control is very difficult without causing extensive damage to the shoots. Repeated applications, because they won't go without putting up a fight, with garden chemicals can do almost as much damage as the aphids themselves. By spraying now with something like a soap solution or Neem oil, that works by suffocating them, you can quickly eliminate future problems. So today's tip is check for aphids, not just on your Japanese maples, but on all your trees and shrubs. That way you won't have any unpleasant surprises next spring!

Need more information? Get it at growing japanese maples.