Planting and Spacing

Since Fowler Nursery, Michigan’s primary source of the cultivar ‘Colossal,’ stopped producing chestnut stock in 2008, we have started to work with Forrest Keeling Nursery in Elsberry, Missouri. We provide Forrest Keeling information, seed for rootstock and scion wood for grafting. They do the grafting and rootstock production using their patented RPM® system which they suggest provides the trees with unique fibrous roots. Th system does appear to produce fibrous roots as they contend. We have not done a scientific experiment to see if this is any better than regular non-fibrous rootstock because of the limited amount of stock available; but we seem to see a strong trend toward good survival and better growth in the first year. 

Forrest Keeling has also suggested that we plant their stock in the fall. This is probably the biggest change for Michigan chestnut growers and something for which Michigan growers will need to adjust. This is an important aspect of Forrest Keeling production. We have tested this, and in only a one exception, in the coldest orchard we know of in the thumb, the trees have faired well with fall planting. 

Why fall planting? First, Forrest Keeling uses potted trees, unlike Fowler Nursery who sent their material as bare root. When planted, Forrest Keeling managers state that the roots continue to grow in the relatively warmer soil, even when it is “cold outside” in the fall. You should irrigate and keep them moist through the early part of fall if it is dry. Don’t flood; just don’t let them get too dry going into winter. This eliminates the problem of what to do with trees during the winter months (Forrest Keeling’s concern as the plants are ready to be planted in the fall and the extra winter adds nothing to their survival in Missouri) and it gets the trees in for the spring season. You know what happens with spring plantings, right? Plant the trees too early and they bud out into a frost and die back (very hard on young stock), or plant too late into the heat of a late spring and you cannot get them enough water to survive. So, it seems the fall plantings are a reasonable answer to this age-old problem of when to plant. You also have all summer to prepare the ground and dig the holes for the trees.

It seems like there are always unknowns regarding new grafted material. You may expect to lose 2 to 10 percent of a new planting, but no more. If you lose more than 10% of your planted material, something may be wrong. But remember, just as there are good growing and yielding seasons, there are also good planting seasons and bad planting seasons. Droughts, heat, cold, insects, and deer take their toll. 

Keep track of your cultivars and the time of planting. The more notes you take on the planting the more chances you have of answering why something may have occurred. Plant half a row and then realize you need to be somewhere so you don’t finish and put things away, you may not have a chance to get back to it for a couple of days. That needs to be noted. Changing nurseries or cultivars in a row needs to be noted. Trees that look bad, but you plant them anyway should be noted. If you do get top death after the planting (by frost, deer, or weather events), note where the growth starts up again to make sure it was above the graft union so you can tell if the resulting tree is rootstock or from the grafted cultivar. Sometimes this is difficult to determine, but it gets harder to tell the longer you wait.

Overview

With so many Michigan chestnut orchardists having problems establishing chestnut orchards in the 1980’s and 90’s, Michigan State University researchers decided to focus their efforts on one cultivar. That cultivar was ‘Colossal’. If lessons could be learned from ‘Colossal’ plantations, then researchers would be able to teach others about this cultivar and have a comparison to use for other cultivars. Using a newsletter and meeting format, information has been fed to chestnut orchardists through the non-profit chestnut research and education organization, the Midwest Nut Producers Council (MNPC). In 1996, members of the MNPC bought a couple thousand ‘Colossal’ chestnut trees and its pollinator ‘Nevada’ from Fowler Nursery and together learned how to and in many cases how not to treat the trees. We expect the following information to be useful for other cultivars.

Establishing your orchard; site selection

Many factors determine the suitability of a site for chestnut production. A good, well-drained, relatively fertile soil is most desirable. Generally speaking, the more sandy loam and organic matter there is, the better the soil unless drainage is a problem. Often, soils with considerable clay or organic matter are low and poorly drained. Soil types, drainage, texture, and the amount of organic matter in Michigan soils can vary markedly even within a small area. The importance of a careful soil survey prior to planting cannot be overemphasized as this may help to prevent mistakes that the grower will have to contend with for the life of the orchard. (Read: Before Getting Started in the Post Scripts Section at the end of this handbook).

Chestnut orchards can only be established on well-drained soils where the pH varies from 5.5 to 6.5. From experience, the pH can be lower, but it cannot go much higher without nutrient problems developing. We have seen the burning of young shoots and leaves associated with pH below 4.5. A pH above 7.0 leads to leaf chlorosis and stunted growth (Figure 1). If you cannot meet these basic features with your land, do not attempt to grow chestnut or be prepared to constantly neutralize these constraints. 

Planting on hills is better than on flat land. That not only provides good water drainage, but you need to consider the drainage of frost and the development of frost pockets which have a tendency to develop and harm trees on flat land. Wind, at first, will seem to plague trees on ridges, but we have seen little harm. In fact, wind movement on ridges may help prevent frost. Trees have a tendency to bend on windy ridges, so make sure to stake them toward the wind to prevent the permanent bending of the main trunk.

Soil nutrition problems Soil nutrition problems
Figure 1. Most soil nutrition problems can be solved with soil and tissue analysis. Some would add micronutrients, but here the plant on the left needs to have its soil pH adjusted first. The chlorotic weakened planted on your left is more susceptible to attack by insects. The plant on the right is healthy.

Transplanting: Nursery trees are available as container-grown, bare-root or large-tree transplants. Forrest Keeling Nursery ships their trees in pots.

Bare Root: Many species of trees including chestnuts respond well to bare-root planting. A greater portion and longer roots are retained after digging or removing from the nursery. Also, the roots are easily inspected at planting time. Damaged roots can be trimmed and girdling roots can be removed before planting. Bare-root plants should be planted while they are completely dormant. Large sized bare-root trees might require staking. 

Container Grown: The advantage of using plants grown in containers is that 100% of the roots are in the container. Thus, the plant goes through limited transplant shock if given adequate follow-up care. The main disadvantage of container-grown plants is the possibility of deformed roots. “Root bound” plants have roots circling inside the container. The entangled roots are a physical barrier to future root growth and development. If this condition is not corrected at planting time, the plant may experience slow growth and establishment because of the girdled roots.

Therefore, we now recommend Forrest Keeling Nursery planting stock. We have worked with them to establish some of our best cultivars for Michigan on their RPM® patented rootstock. This material should help transplants get off to a better start because the roots of their trees are not root bound and are fibrous. These young trees are normally planted in the fall.

Potted trees from Forrest Keeling: Usually, Forrest Keeling Nursery is ready to ship trees in September. We have verified that potted trees can be planted in mid-September to mid-October as the usually cool temperatures and adequate rainfall make autumn a good time to plant trees. Also you should consider the soil may be warmer and less damp than in the spring. But also fall-planted trees will demand extra attention because these trees may not have enough time to establish a good root system before winter sets in. Cold winter winds and sunshine cause plants to lose water from their branches, so roots need to be well established to replace the water if trees are to survive.

It is very important to provide water to the root system of the potted tree (Forrest Keeling trees come with a porous soil that demands lots of water even after planting in the ground). Water plants thoroughly and when needed supply about 1 inch of water per week. Continue watering until the ground is frozen. Wrap the trunks with the plastic mouse-guards (tree-guards) by late November to prevent frost, sunscald, and animal damage. Be sure to remove and reset the tree-guard sometime after April so it does not girdle the trees.

A 2 to 4 inch layer of mulch can help prevent wide soil temperature fluctuations. Apply materials such as shredded bark, pine straw, or typical wood chips in late November, after the plants are fully dormant and the soil is cold.

With that said, is it really safe to plant trees at the end of a growing season and close to winter in Michigan? The answer to this question is still not completely known. In the past two years (2010 and 2011) we have planted trees in the fall and we been seen many more positive results than failures. We are discovering that Fall planting can be successful as long as you do not plant too late into the Fall, and if proper care (watering, mulching, staking if needed, etc.) is administered after planting. But if fall planting is extended into November and December, root growth may be poor and planting failures will probably occur.

In summary, fall planting (mid-August to mid-October) takes advantage of favorable soil temperatures and moisture conditions that promote the root growth needed to sustain plants through their critical first year in the soil orchard. Unfortunately, our mid-western climate is unpredictable. However, even the toughest plants may die if fall or early winter weather is severe or comes early. But if healthy, vigorous trees are chosen, if proper post-planting care is given, and if slow-to-establish species are avoided, fall planting of trees and shrubs can be as successful or better than spring planting.

Large Tree Transplanting: Mechanically dug, these trees require excellent soil conditions and frequent irrigation to help them repair damaged roots. We have moved ‘Colossal’ chestnuts after two full growing seasons and before the third. The roots were hand dug after a backhoe cleared most of the soil from around the root zone. The trees survived their transplanting and produced flowers during their first season in their new location. But we have also witnessed trees that struggled after transplanting. The best way to do this is to take the largest root ball possible and move the tree to an excellent site for recovery.

Planting Techniques for all trees: The correct planting technique begins with the loading of the plant at the nursery or at the site where you will pick up your trees. Chestnut growers should be very careful with the plant material received. Always protect the roots, and stems during transport. The plant tops should be shielded from winds. When you arrive to pick up your trees, don’t bring an open back pickup truck unless you have tarps with which to cover the plants. Few plants, whether dormant or vigorous can stand continuous 70 mph winds even if the roots were not connected to a water source. Never pick up a plant by the trunk. Trees are particularly vulnerable to damage if growth has started. In the spring the bark is easily injured. If plants must be held or stored on the landscape site, it is best to place them in a location protected from the wind and sun. Do not let the roots freeze or dry out during this time. If the delay in planting is more then a few days, one should heel the plants by covering the roots with bark or some other mulch. ?

?The Planting Hole: Tree holes should be large enough to accommodate the root system with a minimum of root pruning. However, long roots can be cut back enough to balance the root system and to allow planting without crowding or twisting roots to get them into the hole. If an auger is used in wet, clay soil, the inside surface of the hole glazes and seals off, sometimes preventing root penetration. It also leads to the possibility of rain or irrigation water saturating the soil in the hole and not draining out creating a condition of low oxygen. This undesirable glazing of holes can be prevented by digging the holes a few days ahead of planting, when the soil is dry or with low moisture. If this is not practical, part of the glaze can be removed by slicing the edges with a shovel at planting time.

Bare-rooted plant roots should be kept in water or be kept moist prior to planting, and, unless the soil is wet, the tree should be watered at planting. Clean soil, preferably topsoil, should be put around the roots and firmed in with the feet after the hole is about half full of soil. Above all else, do not put chemical fertilizers in the hole at planting time because the roots can be killed by such treatment. Also, the most common problem in establishing new plantings is improper irrigation and lack of weed control. These two problems cause more stunting and plant loss than any others during the first two years of orchard establishment. 

The most important consideration in planting trees is the planting depth. Don’t plant too deep. It is better to plant in a raised manner so the roots will not drown or suffocate. Dig planting holes 2 to 3 times wider than the root ball and the same depth. Locate the root ball on solid soil and not loose backfill. 

A properly planted tree will be more tolerant of adverse conditions and require much less management than one planted in-correctly. Planting technique impacts water quality as it minimizes water, fertilizer and pesticide use. 

Spacing

This is an area of orchard establishment that is still wide open for discussion. Trees planted too close eventually develop poor health, have unattractive shapes and, as crowding occurs, nut production and quality will be reduced. If tree crowding occurs with age, whole trees need to be removed as soon as possible. Pruning will not correct for root and limb crowding. Pruned trees will grow rapidly and soon crowd again. Also, remember that pruning your trees will set back nut production at least a year. Other important aspects are soil type, frost pockets, wind and water drainage. In California we witnessed one major chestnut grower thinning his ‘Colossal’ chestnut plantation by removing every other tree. You will have to do the math to determine the amount of production gained versus that lost by purchasing and then cutting out trees. It seems to us to be a reasonable thing to do as long as you remember to keep the pollinators. You can’t cut those out of the orchard. 

Colossal orchard in New Era

At one time we thought that 18-foot centers would be enough as our cultivar trials are planted at 18-foot centers. But chestnuts only produce flowers in the sun and with chestnuts only 18 feet apart, they soon grow into each other causing reductions in flower and dying branches from shading. With Chinese chestnut varieties which do not always grow as large as Japanese or Japanese-European hybrids (like ‘Colossal’) it would be easier to get away with spacing that is closer together. But 18-20 feet still evaporates within 8 years in most cases.

Branch death
Branch death occurs as the trees grow into each other in a ‘Colossal’ orchard in California.
Trees in orchard
Grower begins to remove trees in orchard, attempting to get more light to the trees.
Chestnut tree
In comparison, this 20-year-old chestnut orchard composed of similar trees (grafted European X Japanese hybrids) in Australia is what growers in Michigan should strive for. You can see the large trees, but each tree casts its own shadow indicating that sunlight lands on the entire surface area of the tree. That’s important because that is where the flowers are borne. Only the internal branches of these trees are shaded, where flowers are not produced.

With more and more ‘Colossal’ orchards being established, it was suggested that trees be planted every 20 feet with the planned ultimate removal of every other tree such that spacing becomes 40 feet apart after they begin to grow together. That requires a serious calculation to determine how much a tree costs and much you gain from twice as many nuts early in the production cycle before every other tree is destroyed. 

Colossal orchard in Ludington

Another option was to plant 30 feet apart and keep all trees. You will have fewer trees from the outset and fewer nuts during the early years of the orchard, but there would not be the expense of tree removal or losses due to shading and competition. 

Colossal orchard in Hudsonville

But in the 2000 growing season a serious problem regarding both spacing and pollination developed. With the 1997-‘Colossal’ trees beginning their fourth growing season, 3-4 pounds of nuts were expected from each tree in the orchard. Emphasizing this expectation were the large number of flowers, which soon turned into burs, which stayed attached to the trees well into September. A large harvest was expected, but then in mid-to late September the burs fell empty, un-pollinized flat, shriveled nut in most cases. A few growers received 2 pounds of nuts per tree but most growers had many empty burs and only a few pounds of nuts for the entire orchard. What went wrong? 

Pollination study in 2001

We believe that the pollinators were too small and too far from the trees they were expected to pollinate. Analyzing a grower’s orchard where pollinators and nut producers were in a straight line, showed that only the two closest trees on either side of the pollinator ever produced more than 1 pound of nuts and in some cases these “close” trees produced 3 pounds in their fourth year. Close was 24 feet apart. As soon as trees in the straight line were more than 24 feet apart the number of nuts were reduced to less than a pound (usually just a small handful). Because the trees were in a straight line we could not determine the effect of the wind from west to east. There was seemingly no effect of the wind going from south to north as you might expect with the winds blowing from the southwest in the summer. In fact, the worst position for nut production was the north portion of the orchard. The tree in the center of the long line of trees next to pollinators had the best yield. 

When looking at the cultivar trials where most of our yield data were obtained, we see that the trees are randomly planted, pretty close to each other due to the lack of space available at the research stations. So each tree can pollinate any other tree and they are close to each other. Here we thought that pollen blows 500 feet on the wind, and maybe it does, but not from small, young trees. 

This requires a re-visit of the spacing situation taking into account tree growth, tree removal and pollination (see Figure 2). Earlier we published a planting plan that would accommodate both problems. In this planting plan we suggested two planned removals of trees. At first the trees would be planted close together and then a few years later, some trees would be removed and a few years later more trees would be removed and the remaining trees would have great access to sun, soil and nutrients. 

Differenty types of spacing
Figure 2. The different types of spacing that can accommodate your land and the type of tree.
Main cultivars and pollinators
Figure 3. The combination of your main cultivar (MC) and the distribution of your pollinators.

The spacing examples in the figures below may help you understand some of your planting options. 1 = first tree for planned removal in year X. 2 = second tree for planned removal in year x + y. 3 = a permanent tree. Remember that both pollinators and production trees must be left in the orchard. In the first several years, pollinators should be no further than 25 feet from production trees. In the schmatics below, remember the first row might be one cultivar and the next row may be another cultivar. The 1’s, 2’s and 3’s are times for removal, not the cultivar type. You should plan to discuss this with experts before initiating major plantings to make sure this is well understood.

Initial planting

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After X years

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After X+Y years

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By following the scheme above, you keep your pollinators and nut bearing trees as close together as possible during the early years of orchard establishment, and then remove trees as the trees begin to overcrowd each other put they will be much better at scattering pollen by then due to their increased age and size. 

Other important aspects are soil type, frost pockets, wind and water drainage. In California we witnessed one major chestnut grower thinning his ‘Colossal’ chestnut plantation by removing every other tree. You will have to do the math to determine the amount of production gained versus that lost by purchasing and then cutting out trees. It seems to us to be a reasonable thing to do as long as you remember to keep the pollinators. You can’t cut those out of the orchard. 

This table has the different tree density more commons. You can decide what tree chestnut spacing you want to plant in your orchard. But also we want to highlight that our planting recommendations is 20’ x 30’ and 30’ x 30’. We want you to stay away from the high-density 15’x15’ is difficult to accommodate the pollinators with your main cultivar (see picture 3). Chestnut trees planted in high density and with European type the trees will become overcrowded very quick and then you have to eliminate almost 2/3 of your trees including your pollinators.

Table 1. The number of trees per acre planted different distances in the row and between rows.

Feet in row 10 15 20 25 30 35 40 45 50
10 436 290 218 174 145 124 109 97 87
15 194 145 116 97 83 73 64 58
20 109 87 73 62 54 48 44
25 70 58 50 44 39 35
30 48 41 36 32 29
35 36 31 28 25
40 27 24 22
45 22 19
50 17

Windbreaks: Poplars have enjoyed an every increasing popularity as a windbreak around orchards. However, we found two locations where poplar tree roots, planted in windbreaks over 30 feet away, reduced growth and flowering potential of ‘Colossal’ chestnut trees. We do not suggest planting poplars as a windbreak, especially in sandy soils where the roots can grow to extensive lengths. If you need a windbreak try white pines.

Planting Tubes: This is what some call a moving target. Overall, most of us went through this phase and don’t want to look back. Planting tubes were originally devised for certain types of trees to help them grow faster in their “little greenhouse”. What we found was that the growth tubes became homes to wasps, killed birds stuck inside, and kept the trees too “green” into winter. The winter would kill the tree and it would send up new shoots. In this process you lost your leader, you lost the scion (resulting in just rootstock growing), you had no idea what was happening inside the growth tube. It seemed like one way to keep deer off, seemed to make it easier to irrigate with a hose (down the tube and out the bottom?), and it was easier to stand back and see your future orchard. As already stated, it did not work out that way.

However, things change and growth tubes have changed. More holes, taller, shorter, different materials—it is hard to keep up with all of the changes. Do any work? We have seen some work. But it had more to do with the tenacity of the grower. Remove the tube in the fall allowing the young stem to harden off before winter, put the tube back on for the winter; pull the tube up allowing the colder air of fall and earlier winter to shut down the tree for winter, drop the tube for winter; pull them off, put them on, or buy state of the art tubes with more holes and more sophistication. If this is your primary method of deer control, find a better way. If you think you are getting more growth and faster growth than without tubes, it better be significant for all of the work you have to do.

Tree (Mouse) Guards: We abandoned the tree tubes for stakes and mouse guards. But we plant inside of deer fences for the most part. We stake the tree with conduit pipe or wood, tie the tree to the stake and then place a mouse guard on it. The mouse guards come in different lengths and really need to go down into the soil to guard from field mice that can eat the bark off the tree around the soil line. It is usually an above ground chewing, so the guard needs to be embedded in the soil. Some years there will be no problems, other years it can happen to 50 percent of your trees.

The tree guard or mouse guard looks like it has a spring-like coil and will expand with the growth of the tree. This will not occur. Instead, if you do not take off the guard and put it back on at least once a year, it can strangle (girdle) the tree and do more damage than the mice.

Don’t forget about your tree guards!

Don’t forget to take off and adjust the white tree guards. These tree guards work well to prevent physical damage of the main stems caused by either mammals or equipment. But they should be adjusted at least twice each growing season. They do not expand on their own. Here you can see the spiral effect on the trunk of a tree this summer. You can even see the protrusion of the bark through the tree guard holes.

Preventing Sunscald: Phone calls come in periodically indicating that chestnut blight has attacked an orchard. I will go to the orchard and usually find a canker similar to the type of canker (infection area) caused by the chestnut blight fungus on the base of the tree. But it has rarely been chestnut blight. It is usually a problem called sunscald or “southwest disease”.

As was mentioned above, young transplants and thin-barked trees are susceptible to an injury called “sunscald” during the winter and early spring. Chestnut trees have big problems with sunscald in the Midwest. In California, the scald occurs in the summer but in Michigan we believe the scald occurs in the winter and early spring. The surface temperature of trees is elevated above that of the surrounding air by the absorption of sunlight. This rise in surface temperature occurs long enough to make cells in the bark active and thus vulnerable to injury during the sudden nighttime temperature drop. Growers need to paint their trees with a white latex paint diluted 50% with water. Paint high enough to protect all parts of the trunk (up to and beyond the crotch). The paint should be indoor, cheap, white latex diluted with water. This reduces the amount of preservatives in the paint that may (no proof) damage the tree. This should be painted up the trunk of the tree to where the branches form and break into the scaffolding of the tree. If the sun hits it, it can be damaged. Only 180 degrees of the tree need be painted. It can be painted on with a brush or sprayed on the tree.