WILL ADDING MULCH TIE UP NITROGEN IN THE SOIL?
This question comes up frequently and as with most questions, the answer is “It depends…”
Adding pretty much any kind of mulch as a top dressing (laid on top of the soil and NOT incorporated into the soil – that is a critical distinction) will not tie up Nitrogen (N). What does tie up N is incorporating non-decomposed material into the soil.
Fully decomposed matter has a low carbon to nitrogen (C:N) ratio. Material that has not been fully decomposed has a high C:N ratio. To understand why this matters, we need to understand something called a nitrate depression period and the basic needs of the organisms in the soil whose job it is to decompose stuff.
Decomposition by soil organisms is a good thing. We want that to happen. This is what builds organic matter in the soil, providing so many benefits for healthy soil and healthy soil ecosystems. And is, in fact, the topic of another blog. We will go with the short version here.
Microorganisms have a body C:N ratio varying (depending on the species) from about 5 to 10 carbon to nitrogen. The ratio of 8:1 is often used for simplicity. They have to maintain that in order to survive. It isn’t optional. During their day-to-day job of decomposing matter, they use approximately three times as much carbon as nitrogen. This is why recommendations of anything we incorporate into the soil should be no more than 24:1. If a high C:N product is dug into the soil, the organisms have to scavenge the soil for the nitrogen to maintain that ratio. This can tie up N making it unavailable for other organisms, such as our plants, until they have brought the ratio back to a suitable level. Still with me here?
Examples of a suitable ratio product (24:1 or less) would be fully decomposed compost, some grass clippings, some aged manures, and many of the meal products (such as alfalfa, corn, linseed). These may be incorporated into the soil and, in fact, generally contain some amount of available N. And, yes, going into the properties of the multitude of soil amendments is a topic for another (if not several) blog(s).
Examples of higher C:N ratio products you would want to use as top dressing only would include whole tree chips, bark (shredded or nuggets), compost incompletely cured, cardboard and paper products. Side bar: cardboard and paper products are often incorporated into the mulching process as a weed-inhibiting layer with a top dressing applied on top. And, you got it, a topic for yet another blog.
Organic products used as top dressing are excellent for regulating moisture and temperature of the soil, it protects the soil surface from erosion by wind or rain. They can protect the soil from crusting caused by the impact of rain or sprinkler irrigation. It gradually breaks down and is incorporated into the soil by biological activity which improves soil quality and releases nutrients slowly. At that point, it no longer has a high C:N and, therefore, does not tie up N.
So the bottom line is to determine your purpose and then make your choice suit the purpose. Do you want to immediately increase the organic matter content of your soil? Purchase a product that is fully decomposed. Do you want to protect and improve your soil from the top down? Purchase a product you can use as top dressing.
A follow up question is often “how do you tell if it is fully decomposed”? It should crumble between your fingers and be dark brown all the way through. If it doesn’t crumble, it isn’t fully decomposed whether or not it appears the same color all the way through.
Now what about manures? They crumble even when fairly fresh. Most manures are in the relatively “safe” zone, with fresh horse manure being a bit high.
A concern with some of the manures is less about the C:N ratio but more about herbicide contamination, high levels of phosphorus (P) and potassium (K) and the possibility of excess soluble salts. But, as stated above, that discussion will appear in another blog.
WHEN IS THE BEST TIME TO PLANT A TREE?
There is an old saying that states the best time to plant a tree was 20 years ago; the next best time is now.
Trees take time to grow and mature and humans are basically impatient. Many people think they won’t see a tree mature in their life time, so put off planting them at all. But the reality is you may very well see a tree you plant gain substantial size in your lifetime. It may not be fully mature but it has the potential to become significant. And you are leaving a legacy for a future you helped to improve. So go ahead, plant a tree. Plant lots of trees!
Now getting down to more specifics: when is the best time to plant a tree when considering seasonal influence. Some say spring, some say fall. As with everything: it depends.
Here in our region (remember, we live in Montana) my preferred time to plant is spring. The reasons being: 1) you will have better selection at the nurseries and 2) the tree will have a longer period to settle in and establish prior to winter.
Fall planting is problematical here due to the possibility of early onset of winter. A tree should have at least 6 to 8 weeks to establish prior to the ground freezing.
If you live in an area that does not freeze, fall may be fine. In fact, some prefer it as roots may develop during the early fall in these areas, putting necessary resources into developing a new root system. But as soil temperatures go below 32 deg F, everything slows down to a crawl.
Nurseries in more temperate areas may maintain a selection of quality species as well as variety through fall. However, in some of the more northern areas where winter sets in and the ground freezes hard, stock of new trees generally comes in in the spring. By fall, yes, the nurseries may have good sales, but the selection is limited. You might find a great deal or you may not. And, again, you want to get that tree in the ground with 6 to 8 weeks to settle in.
When is the Proper Time to Prune a Tree?
This is a common question arborists are asked. The answer begins with a phrase you will hear me say frequently, “It depends….”
There are no hard and fast rules or answers. It depends on the species of tree, the condition of the tree, and the purpose for the pruning.
Many people have heard it is best to prune during the dormant season, but this is only applicable in some circumstances.
Being proactive in your pruning schedule will be cost effective and may save storm damage and costs down the road. A well-maintained tree is able to withstand more impacts than one that has been let go too long, is full of deadwood, cracked limbs and/or hangars.
Some basic suggestions on timing are as follows:
Removing hangars or cracked limbs, mitigating storm damage, pruning limbs causing damage to a structure or creating a hazard can be done at any time.
Generally, a tree will seal over a pruning cut fastest when it is actively growing. Therefore, for general pruning on many species, spring after the first full flush of growth and prior to fall is warranted.
There are always exceptions. One of those being to avoid flight time of a problem pest or the active period of a pathogenic disease.
An example here in our area is the Mountain Pine Beetle (MPB). This is a native beetle which attacks native and non-native pines. Whereas populations are starting to come down in some areas, taking precautions not to attract them to your trees is still a good practice. They are active, roughly June through September. Pruning or removing pines during this window presents the risk of attracting this pest to fresh wounds or debris left on site. So we recommend pruning or removing pines October through April. By October they should be settled for wherever they are going to be for the winter. Fresh wounds on trees emit pheromones which can attract the beetles. Hence, the recommendation to finish pruning or removals well before flight to allow time for these wounds to seal and/or the debris cleared from the site.
There are many other insect pests which can be attracted to fresh wounds in trees. This list varies region-to-region. Find out what your problematic pests are, their life cycle and flight times as well as their host species. Avoid pruning during those times.
The same philosophy applies to avoiding times when pathogenic diseases are sporulating or when environmental conditions are suitable for dispersion. Some diseases are dispersed by rain, so pruning while the tree is wet or during a rainy period can pose a greater risk of spreading the disease. Thyronectria canker in honeylocust, Gleditsia triacanthos, is an example here in our area.
Many shade and ornamental trees only need periodic pruning.
If pruning the crown for clearance on a non-emergency basis, such as for mowing, pedestrian, vehicular, or structural conflicts, it is most effective to prune after the tree has fully leafed out for two basic reasons: 1) you will get a more accurate assessment of the amount of clearance achieved if they are pruned when they are heavy, and 2) the pruning will last longer.
If pruned prior to leaf emergence, a tree will re-establish that amount of growth quickly. If pruned after its spring flush of growth, it will not.
It is unreasonable to suppose all work may be performed at the optimum time for every tree. However, planning ahead and calling your arborist well in advance may allow your tree to be pruned during the appropriate time period.
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