Cucumber Grafting • Advantages • Materials • Technique
A Hensley's Seed Co. guide
Introduction to Cucumber Grafting
Grafting a tender cucumber variety onto a rootstock with a tougher, more vigorous root system is a practical way to get more from your crop, especially early in the season. Any cucumber can be grafted, but greenhouse varieties usually benefit most. Their vines tend to be more delicate than field types, so a vigorous rootstock helps them more. Their attractive, tender fruit also sells at a premium, particularly when field cucumbers aren't available, which helps pay for the extra labor grafting takes.
Many rootstocks are available, but interspecific hybrid squash are widely regarded as among the best choices for early greenhouse and high tunnel cucumbers. A well-done graft can help plants cope with cold soil, bring the first harvest forward, improve overall health and stress tolerance, and may raise a grower's net returns.
Tips for a good grafting outcome
- Run a germination speed test.
- Make several sowings of both rootstock and scion.
- Sow about 25% more rootstock and scion than you need.
- Practice the technique first.
- Set up a reliable healing chamber.
- Keep records.
Cucumbers are commonly grafted in one of three ways:
- splice-/top-grafting
- hole insertion
- side or tongue-approach grafting
Each can work well, but next to hole-insertion and side grafting, top-grafting is easier, and anyone who has grafted other vegetables will probably find it familiar. The guidelines, steps and tips below will help you get started.
Required Materials
Scion cucumber varieties
Most greenhouse cucumber varieties respond to grafting in much the same way. Two that do especially well are 'Katrina' and 'Socrates', since their vines are more tender than those of other greenhouse types such as 'Corinto'.
Rootstock variety
A good rootstock choice is 'Tetsukabuto' squash (Cucurbita maxima × C. moschata).
- Scion seed (the fruiting variety on top)
- Rootstock seed (the root system below)
- Growing mix of your choice
- Plug trays in the cell size you prefer
- Shallow leakproof trays
- A disinfectant such as Virkon® or bleach diluted 1:10
- A classic double-edged razor blade
- Grafting clips*
- Thin plastic straws or something similar to support each grafted seedling
- A spray bottle or hose mister
- 7" Humidity domes or a dedicated healing chamber
*Cucumber and cucurbit rootstock stems are much thicker than tomato stems and those of other commonly grafted vegetables, so cucumbers need larger clips, with openings of 3.0 mm or more. Spring-loaded side-grafting clips work well for both top grafting and side grafting.
Seeding Your Cucumber Scion & Rootstock
Germination speed test
Before sowing the full batch, sow 10 seeds of each variety you plan to graft and compare how quickly the rootstock and scion germinate and grow.
It's also worth noting your light, day and night temperatures, humidity and ventilation, in case you need to adjust or repeat them later.
For the main sowing, you can then time things so the rootstock and scion hypocotyls are as close in diameter as possible just as both are showing their first true leaves.
Sow about 4–5 weeks ahead of your planned transplant date, adjusting for the temperature and light in your growing and healing spaces. Healing adds 1–2 weeks to seedling production compared with ungrafted cucumbers.
Cucumbers tolerate mismatched stem sizes better than crops like tomatoes, but a close match still gives the strongest union. Cucumber and squash hypocotyls differ enough physically that a perfect match isn't realistic. You don't need one; just know that the closer the diameters, the better your odds.
A widely used cucumber rootstock is 'Tetsukabuto' , a hybrid between two squash species, Cucurbita maxima and C. moschata. That wide cross gives strong hybrid vigor and advantages over a cucumber's own roots, but it sprouts and grows at a different pace than cucumber. Because the two differ so much, practicing the timing between sowings is especially important. Making several sowings of each and sowing about 25% more plants than you intend to set out improves your chances of matching stems and still reaching your target plant count. A germination test also helps you pin down the right sowing time for each variety. (See box.)
Good germination conditions, 85–95°F/29–35°C with high humidity and darkness, go a long way toward fast, even emergence of rootstock and scion. A germination chamber, soil thermometers, moderate moisture and lukewarm water help too. Expect seedlings in 5–7 days. To prevent stretching, give them good light soon after they emerge and hold a steady 75°F/24°C for the next 7–10 days. Watch growth rates and slow down any variety racing ahead by cutting back water or temperature. Below 55°F/13°C, growth can stall for a while.
From sowing rootstock and scion to setting grafted plants into greenhouse soil or soilless media usually takes 4–5 weeks.
Top-grafting Process
Pre-grafting set-up
Seedlings are usually ready about 5–7 days after emerging. Graft when the first true leaves on both scion and rootstock are just starting to unfold.
- It's the best stage for the scion since leaf area is small, which limits water loss after grafting, yet the seedling has had time to store enough carbohydrate to carry it through healing.
- It's also the best stage for the squash rootstock since it's mature enough to survive grafting, its hypocotyl is still close to the scion's size, and if you wait longer the stem starts to go hollow, which makes the graft far more likely to fail.
Ideally your staggered sowings will put scion and rootstock at this stage with stems as close in diameter as possible.
Set up a clean workspace out of direct sun for cutting. Indoors is easiest to keep comfortable, but a shaded, not-too-hot (70–74°F/21–23°C), not-too-dry spot in the greenhouse also works. Stay away from fans and drafts; plants dry out more slowly when grafting isn't done somewhere hot, dry or breezy.
Cleanliness matters, because a pathogen on your hands or tools can be passed to every plant you graft. Wipe down the workspace with disinfectant first, and always begin with new or sanitized blades and clips.
Break a double-edged razor blade in half lengthwise while it's still in its paper wrapper. Be careful: these blades are thinner and sharper than most.
A good healing chamber is one of the most important parts of grafting vegetables. Fresh grafts need a protected spot with steady, ideal conditions until the union takes, so you'll want to control light, temperature and humidity. Keep plants humid (80–100% relative humidity), out of direct sun, and at 77–89°F/25–32°C.
These conditions help scar tissue form fast and keep respiration low until the vascular tissue reconnects. For small batches, 7.5"-tall humidity domes over each flat work well; larger operations may find a plastic tent covering many plants more practical. Put the healing area close to your grafting bench so plants are moved as little as possible.
Water plants thoroughly about 8–12 hours before grafting. Roots that are too wet push excess water up the rootstock stem, which can force the scion off and lower your success rate. Soggy plants and media are also harder and messier to handle. Still, plants need enough water to last the critical 5–7-day healing period without watering.
Practicing
If you're new to grafting cucumbers or using a new healing chamber, sow some old cucumber seed for practice and learn how to run the chamber at the same time.
That way you can review and refine your technique without risking much.
You can also practice by grafting spare scion seedlings back onto themselves, to get the feel of the cuts or to train new grafters.
Top-grafting
The main risk with top-grafting cucumbers is that fresh grafts run out of energy before they heal, which sharply lowers survival. To help, leave one cotyledon on the rootstock while removing its growing point and the other cotyledon. That remaining cotyledon adds stored carbohydrate, giving the graft enough energy to take more reliably and quickly. Since this is standard practice, cucumber top-grafting is sometimes called one-cotyledon grafting. If you're used to grafting tomatoes, keeping a cotyledon on the rootstock may feel strange at first.
Step 1.
Choose a rootstock seedling whose stem matches your scion's diameter. Cut carefully between the growing point and one cotyledon, angling down to remove all the growing-point and true-leaf tissue along with the second cotyledon, without taking the first cotyledon or cutting too far into the hypocotyl. (See below.)
This fiddly cut takes practice to do quickly and well. It's usually made at 45–60°, but a simple guide is to aim for a cut face about ¼" long. That gives enough surface to join the scion without being so steep that it won't fit in the clip or extends past the overlap with the scion.
If the cut is too shallow and leaves some of the growing point, it will regrow and compete with the scion. Early regrowth often kills the scion, and even when the graft takes, leftover growing tissue can make the rootstock send out its own vines. Caught early, though, regrowth can usually be pinched off after healing and before transplanting.
Step 2.
Take the scion whose stem matches the rootstock and cut its top off below the cotyledons at the same angle as the rootstock cut. Throw away the scion's roots. (See below.)
Step 3.
Set the cut scion on the cut rootstock so the faces line up exactly, for the most tissue contact possible. Any air or soil between the faces will stop the graft from healing. Ease a grafting clip around the joint to hold the two together, making sure the scion doesn't shift. Keep the clip handle at a right angle to the stem so it holds the scion firmly. (See below.)
Push a thin plastic straw through the loop on the back of the clip and into the growing mix for extra support while the plant heals. (See below.)
Unsupported grafts can flop over. Join the rootstock and scion soon after making the cuts.
Healing
As noted earlier, healing matters as much as the graft itself. Start new cucumber grafts at 100% relative humidity and 77–89°F/25–32°C, and watch the chamber temperature closely so it doesn't go above 95°F/35°C.
The first 3–4 days are the most critical. For the first 24–48 hours, keep humidity at 100% and plants in near-total darkness; gently misting the chamber and plants is usually enough to reach that. The idea is for plants to rest, not photosynthesizing or transpiring, while the union starts to knit. After that, bring them back into light gradually, since prolonged darkness slows healing. Fluorescent light at about 200–400 μmol/m2/s is enough during healing.
Over days 3–7, ease plants back to full light and lower humidity with small changes every day or two. How you do it depends on your setup; the flowchart below offers general guidance. Keep lowering temperature and humidity over the next few days until they match normal greenhouse conditions. Wilting means humidity dropped too fast; stretching means healing is far enough along that the plants are growing again and would benefit from more light.
Healing takes roughly 6–7 days in all.
When moving plants from indoors to the greenhouse, take extra care to avoid shock; move them during cloudy weather or put them under partial shade. After a few days back in greenhouse conditions, they can be handled and watered normally.
Clips usually loosen as the stem grows and drop off on their own, and you can gather and disinfect them to reuse.
Transplanting
When transplanting, keep the graft union above the soil line; otherwise the scion may root into the soil and cancel out some of the benefit. Remove any shoots that sprout at or below the union, since they come from the rootstock and will quickly outgrow the scion. Also consider wider spacing than for ungrafted plants so each can carry more leaders, and adjust fertility and other care to get the most value from grafted plants.
Because grafting adds time, effort and cost, trellis and prune grafted plants with a lower-and-lean system (or something similar) rather than the umbrella method to get full value from them. Otherwise, grafted plants need much the same care as ungrafted ones, though their stronger vines may need lowering sooner.
Learn More
Resources
- This guide as a printable tech sheet (PDF)…
- For more on growing practices, see our greenhouse cucumber growing (tech sheet, PDF)
- Visit our More about cucumbers…
- Visit our More about grafting…
- Visit our More about pruning and trellising…
- Browse our Greenhouse cucumber seeds…
- Browse our Supplies for grafting…
