How to plant a tree

I’ve been working with a homeowner to trim a few trees and remove some trees during their new home construction/remodeling process. The house is done (it turned out fabulous!) and it’s time to plant some new trees. Some for shade on the west side of the house (“Death Valley”), some to screen less than desirable views, a screen for a power poles, etc. The homeowner is very knowledgeable about plants and their requirements. She came up with many of the species we will use, and relied on my recommendations for others.

The plan called for three species of ash trees (Fraxinus greggii – Littleleaf ash, Fraxinus velutina – Arizona Ash and Fraxinus udhei – Shamel Ash), two species of oak trees (Quercus suber – Cork Oak and Quercus virginiana), a Vitex agnus-castus, three Arizona Cypress – Cupressus arizonica, and five South American hybrid Mesquites (Prosopis sp). A nice selection! It is always nice to plant a variety in case a disease, insect or environmental conditions cause some trees to do poorly.

Because their growth often outpaces larger container sizes, and because of cost, we decided to use 24” box size trees. (Here in Arizona, field grown “ball & burlap” trees are usually not available – we  typically have a selection of container grown trees.) Larger box sizes increase in price at the nursery in an exponential fashion. Also, it becomes difficult to handle larger sizes without using heavy equipment, which increases planting costs. Unless someone needs a very large tree immediately (I mean RIGHT NOW!), it is usually best to stick with smaller sizes.

The quality of the nursery stock is also a huge concern. I have preferred suppliers in Phoenix who know how to handle the plants as they grow. Each time a plant is moved from one container size to another (“bumped”) they need to ensure that the roots are manually straightened or pruned at the edge of the container. If this is not done, you can end up with a root system that looks like this:

A really messed up tree! We replaced it with a 24" box Mesquite.

This poor Mesquite tree had a number of problems which ensured it’s eventual demise. First, the nursery which propagated it failed (at the 1 gallon container size) to do any root pruning when they bumped it. The roots that were circling the inside of the container can still be seen inside the “root ball” from the 15 gallon container. These roots will never straighten themselves out. They will swell in size along with the tree’s trunk, eventually strangling the tree. They will never straighten themselves out! The will keep the roots from anchoring the tree in winds which will cause it to blow over in a storm. They would have been invisible inside the 15 gallon container’s soil – the nursery who planted it never knew… But, they should have dealt with a propagator that knew what they were doing!

The nursery that planted the tree also planted it too deep. A tree’s trunk was made to be in the air. A tree’s roots were made to be in the ground. Simple? But, a tree’s roots need water and oxygen to grow – that is why you sometimes see a tree’s roots rising to the surface – that is no problem. If you bury them under more soil it could be a problem… But, it is very important to plant a new tree at exactly the right depth. The “root flare” or “root crown” should be right at the surface. This poor Mesquite tree was planted at least 6” too deep. You can see roots trying to grow out of the sides of the trunk (adventitious roots)! Trees planted too deep are under continual stress which can lead to their premature decline.

This poor tree also had some girdling roots at the 15 gallon container size which were not properly trimmed off by the nursery who planted it. This also could likely have killed the tree in time.

When planting new trees we rarely stake them. Staking is not usually necessary and causes more problems than it cures! The ties often end up getting grown into the trunk, or girdling it. The stakes are usually so weak that they would not hold the tree up anyway! A tree grows “reaction wood” in response to it’s need for strength in certain places. A large horizontal branch, for instance, would add wood in places to reinforce it and keep it from breaking off. A tree that is staked won’t develop a root system strong enough to support the tree, creating a real problem!

Sometimes we will need to stake a tree if the top is too whippy to stand up, or if it wants to lean in a way that we don’t want it to. These stakes are temporary – 6 months to a year at most. If the tree will still not support itself by then, it probably never will!

We have taken out a lot of storm-damaged trees this winter, and almost all had root problems. Either girdling roots from the nursery (or time of planting), or roots that didn’t develop because of poor irrigation practices (which I’ll try to cover in a future post).

The poor Mesquite tree above was staked! An animal (rabbits?) ate the bark off one side, killing about half the trunk. Then a wind broke the tree off just above the stakes. What a mess! We replaced it with a 24” box Mesquite with a good root system – and no stakes!

Back to the big tree planting project for the new homeowner… We had enough trees that I could get them delivered and didn’t have to go pick them up! Moving a 24″ box tree is usually pretty easy for two people. The weight depends on what exactly the nursery used to fill the box. Wet clay soil can be VERY heavy, dry organic mulch can be light. It is really nice to have a third person around for the heavy ones!

Unloading a 24" box is AT LEAST a 2-person job!

As we were unloading, there was a problem - one of the trees was not very nice (the Vitex agnus-castus). I ended up rejecting it and driving to Phoenix to pick up a replacement at another nursery. It gave me an opportunity to take some pictures for you!

Sunrise among the BIG 60" box trees.

The huge selection at Baseline Trees, one of the Phoenix nurseries we use.

We had enough holes that we could get a contractor to dig them with a little backhoe. Hand digging 14 holes would not be very fun! The holes need to be at least 3-4” wider than the container. For 24” box trees that ends up being 30” to 32” square. The holes should be just as deep as the soil depth in the container – OR SHALLOWER! We usually go about 17” deep for a 24” box (the usual soil depth in a 24″ box). It is important to not dig the hole too deep – the soil can settle and you end up with a tree that is planted too deep! Two to three inches shallow is preferred to being too deep at all.

Skid steer with backhoe attachment speeds hole digging!

We set the wood box in the hole and take off the metal straps which hold it together. Then we remove the box sides. Surprisingly, the box bottom is left on! It will soon decompose and doesn’t cause any problems for the tree at all.

Looks too shallow! Better pull it out and dig a bit more...

After the box is off, we take an old pruning saw and cut off the outside 1” to 1-1/2” of the root ball. This should ensure that any circling roots will be removed. We can’t see inside the rest of the root ball, and have to trust that the nursery we dealt with did a good job!

Sawing the root ball to remove girdling roots.

We use water as we backfill to make sure there are no air pockets around the root ball. We backfill to level, making sure we don’t add dirt around the trunk or on top of the root ball.

This Arizona Ash was tall and whippy, so we temporarily staked it.

You can see in the picture above that we prefer to “guy” trees rather than stake them. It is more secure and more flexible. We use Arbortie which is a soft nylon strap for the guylines. I tie them loose, so that they tree can move in the wind but will be held from moving too much. They are taken off as soon as possible!

We made (temporary) shallow basins around the trees so that the irrigation water will not run off when they are watered with a hose. Normally we would hook up irrigation, but this customer doesn’t have their drip system in yet. That is a project for this fall!

Wood mulch, spread 3-4” thick over the area (but not right up against the trunk!) is a good idea. Studies in Phoenix have proven that the soil underneath wood chip mulch is cooler and moister than soil under rock mulch. (Contact me if you would be interested in a load of chips for mulch, erosion control, or composting!)

The new shoots on a tree produce hormones that stimulate new root growth. New roots produce hormones that stimulate new shoot growth. Normally, things stay well balanced. What happens if a tree loses a bunch of roots during planting/transplanting? Do we prune the top of the tree to “balance” it with the new, smaller root system? Current research says “No!” We need all the shoots we can keep to signal the root system to grow! In accordance with this, we do not like to do any pruning on new transplants except to take off branches damaged in transit.

We’ll be back to tree trimming and some other interesting project – check back and I’ll post more when I get a chance!