Establishing and Managing Root-Training Polybag Rubber Nurseries

A complete guide to setting up and managing root-training polybag nurseries for rubber trees in Vietnam — including nursery design, polybag specifications, seedling preparation, grafting, and root hardening techniques.

---

1. Planting Season, Location, and Design

• Planting season: From July to September.

• Site selection: Choose areas with favorable climate, reliable water sources, and convenient access for management and transportation.

• Nursery design:

  • Ensure good drainage, erosion control, and easy maintenance.

  • Divide the nursery into plots of 20 m × 10 m, with 3 m-wide paths between plots.

  • Large nurseries should have main roads 5 m wide and sub-roads 3 m wide.

  • Plant density: 150,000–160,000 polybags per hectare.

• Support frames:

  • Made of steel with compartments fitted to the polybags, each frame 20 cm wide and variable in length.

  • Arrange polybags in double rows, with 1 m spacing between row centers.

  • Place polybags so that one-third of the bag base is below ground level.

• Shading:

  • Use PE film to reduce sunlight intensity to about 70%.

---

2. Polybag Specifications

• Material: Polypropylene (PP) with a volume of 750 ml and 1.5 mm thickness.

• Shape: Truncated cone — 28 cm long, 8 cm top diameter, 5 cm bottom diameter, with a 2.2 cm drainage holeat the base.

• Internal ridges: Six evenly spaced vertical ridges located 1 cm below the rim to prevent root spiraling.

• Durability: Each bag can be reused at least five times.

---

3. Preparing the Growth Medium

• The medium should consist of processed plant residue and well-decomposed organic fertilizer, enriched with fused phosphate, SBIO microbial inoculant, and fungicide.

• Fill polybags with the medium two weeks before planting the rootstocks.

---

4. Preparing Rootstock Seeds

• Required seed quantity: 1,200–1,600 kg/ha, depending on design density and seed type.

• Selection and pre-treatment of rootstock seeds should follow standard protocols ensuring seed viability and uniform germination.

---

5. Planting Seedlings in Polybags

• Pre-watering: Moisten the substrate thoroughly 1–2 days before planting.

• Select healthy seedlings with one straight taproot (3–10 cm long) and no deformation or damage.

• Planting steps:

  • Make a vertical hole in the center of each bag equal to root length.

  • Place the taproot straight down, firm the soil gently, and cover lightly.

  • Discard damaged seedlings (broken shoots or roots, albino, or weak plants).

• Within 20 days after planting, inspect daily and replace any substandard seedlings.

---

6. Rootstock Maintenance

• Watering: After planting, water thoroughly to settle the soil around roots.

  • During the dry season, maintain consistent moisture down to the bag base (≈10 liters/m² per watering).

• Weeding: Keep the nursery weed-free manually or chemically.

  • Avoid using PE mulch, which hinders aeration and moisture balance.

---

7. Grafting Techniques

• Grafting period: From January to May.

• Begin grafting when rootstock diameter at 10 cm above soil exceeds 6 mm.

• Perform grafting during cool periods, never when the rootstock is wet.

• Scion wood: Must be of similar age and condition as the rootstock for proper bark separation and graft union.

---

8. Pruning and Transferring Polybags

• Unwrapping: Remove the grafting tape 20 days after grafting and wait at least 15 more days before topping.

• Topping:

  • Cut above the graft union by 5–7 cm (or 10–12 cm for smaller stocks).

  • Seal the cut immediately with vaseline to prevent moisture loss.

• Transfer:

  • After topping, remove the bags from frames, trim roots growing outside, and move them to the root-hardening site.

---

9. Leaf Hardening and Root Training

• Place topped polybags on frames so that one-third of the bag is below ground.

• Maintain 60 cm spacing between frame edges for good air flow.

• Keep the nursery clean, control weeds, remove wild shoots, and apply foliar fertilizers and fungicides as needed.

• Once plants reach one stable leaf whorl, remove the shading net to start root hardening.

Root Training Process:

• Two weeks after shading removal, lift the frames so that the bag base is 5–10 cm above ground.

• Cut any roots protruding from the base and water immediately.

• Continue daily watering and root trimming as new roots emerge.

Leaf Hardening:

• When plants have two stable leaf whorls, reduce watering to every two days until they are field-ready.

• Select uniform seedlings with a stable top leaf whorl for planting.

---

10. Fertilization

• Use blended single fertilizers (Urea, DAP, K₂SO₄) according to Supplement Table 5.

• Timing:

  • For rootstocks: first application after two leaf whorls form; repeat every 30–45 days, stopping 30 days before grafting.

  • For topped grafts: first application 7–10 days after topping, and subsequent ones after each stable leaf whorl.

• Method:

  • Either apply directly (3 cm from bag wall) or dilute in water and irrigate evenly.

  • Always water thoroughly after each application.

---

Supplement Table 5 – Fertilizer Quantities for Root-Training Polybag Rubber Nurseries

---

Field Transplant Preparation

• Clean the planting site, remove weeds and roots.

• Extract seedlings with intact roots and medium from polybags.

• Reinsert an empty polybag into the hole vertically to create a planting cavity.

• Place the seedling so that the graft union is level with the soil surface and faces prevailing winds.

• Firm the soil gently (avoid pressing too hard) and form a small basin around the stem.

• Collect and reuse empty root-training bags for the next nursery cycle.

---

Conclusion

The root-training polybag nursery model enhances root strength, transplant success, and uniform growth for rubber plantations.
By following precise steps in soil preparation, grafting, watering, and root conditioning, producers can ensure high-quality, well-rooted seedlings ready for sustainable replanting in Vietnam’s tropical conditions.