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Nisão Walnut Production Blog Ep. 6 - Spring Grafting

Advanced preparation is vital:

Spring grafting in walnut orchards
Spring grafting in walnut orchards

As we are approaching to spring grafting season, we would like to outline some important information that will be good to take into consideration know by you and your technical teams.

Step 1: Collect information that will guide you

The first step is to take a careful count of the number of plants that needed to be grafted. This should be done according to each variety. Lack of enough pollinators wi

ll harm a young orchard more than a few missing main variety plants; therefore, special care should be given to have a precise count of pollinators.

In a large orchard, plants may be scattered in different parcels with great distances from each other. So just like planning your shopping in a very large supermarket, you should also organize these numbers according to their locations/parcels, otherwise you will end up running from one aisle to the other back and forth.

And finally, if there are significant differences of the size (thickness) of these plants requiring a graft, this should also be considered as a variable, as having a good match of the bud and the rootstock in diameter is an important factor that affects your success rate.

Ideally, we should know, how many plants need to be grafted of each variety, of each significantly different width and their locations.

Grafting Union
Grafting Union

These plants should be marked in different colors that will enable them to be identified from a distance easily. Using different colors on the plant protectors and plotting them on a basic chart will help you with this.

Step 2: Collecting grafting material:

Grafting materials (buds) will determine the variety of the plants that will grow in your orchard. They need to be collected with a very high precision. There should be no margin of error in their variety reliability. Avoid accepting grafting materials from others unless you are sure about their source, and you participate personally in their collection.

Enough grafting materials should be gathered in dormancy period (by late February) and stored in ideal conditions that will ensure their freshness. Grafting materials (stakes) should ideally be obtained in 100-110 cms. As the stake will lose enzymes from its both ends, by having relatively longer stakes, we can ensure to have at least 4-5 usable buds from each stake. We recommend having at least 30 % more buds than the quantity needed to make sure we end up with enough usable ones.

The width of the grafting stake should be as close to the width of the plants to be grafted. In case there are significant differences in plant widths, you should refer your detailed plant count (as described above) when collecting grafting stakes and collect stakes that will match the width of your rootstocks.

All stakes should be placed in groups of same size and variety, as any mix will affect your grafting success and variety reliability. It might also be useful to mark one the stakes in the same color used for the rootstocks in the orchard. Make sure the paint does not cover the buds.

Stakes should be slightly wet and placed in sealable bags. We recommend placing a wet (after removing excess water) newspaper piece in each bag before sealing. The wet paper and the sealing of the bags will help maintain humidity. Bags should them be placed in a fridge that should be kept in + 4 and 6 degrees C. When storing the stake bunches, pay attention not to harm the buds.

Step 3: Timing

Historical Climatic data shows that the ideal time for Spring grafting in Santarem, Portugal is around the end of the first week of April. This is the time that we will start seeing activity in the plant by observing temperatures above 12 degrees at night. Keep in mind that seasons show changes in years, so weather conditions should be observed carefully during this time to make minor changes in grafting time. The idea is to coincide the grafting at a time when the plant activity begins by pushing the buds to open. A non-rainy period should be chosen for the post-grafting time. A prolonged rainy spring will inevitably reduce your grafting success.

Step 4: Cutting of the rootstock

One of the most important factors that affect your grafting success is to deplete SAP from the grafted plant by cutting (usually) the top portion of the rootstock a few weeks before the planned grafting date. Of the two different type of SAP, Xylem SAP is the fluid which is formed by a solution of hormones, mineral elements and other nutrients moving from the roots toward the buds and leaves.

To achieve this depletion, plants (rootstocks) that need to be grafted should be cut at approximately 70 cm height (approx. 10-15 cm above the plant protector) with a slightly angled cut during the second week of March. Do not delay this operation as the depletion (flow of SAP from the cut point) may take weeks depending on the differences in stem and root pressures, mostly caused by the day and nighttime temperatures. In warmer years, the process will be faster.

The plants cut will gradually begin to release SAP from the cut. This may take a few weeks. The grafting should not be done until this flow of liquid comes to an end or becomes unnoticeably low. The cut made will anticipate and accelerate the process of this SAP flow from roots to the stem and will (in a few days) start to cause buds to get larger and change into a reddish color.

Following this last step of preparation, plants should be observed carefully, and their behavior should be noted a few times a week. Keep in mind, plants in different parcels (even in different section of the same parcel with different sun angle) may show different progress, timing, and speed.

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