5) Planting onion sets in a small furrow


In this tip:

  • A)# Onion fly and carrot fly 
  • B)# Planting time
  • C)# C)# Planting onions
  • D)# Mulching
  • E)# Test: planting date (March 20 to May 1) and hay around.
  • F)# Onions planted early May (mid spring).
  • G)# Harvesting and cutting green leaves
  • H)# Cutting hay
  • I)# Further….


Onion sets can be planted in a shallow furrow in the garden soil.  This is above all good when you have a sandy soil. Reasons:

  • Onion plants are better “fixed”in the soil.  After planting, birds will not pull them out that easy.
  • The soil in the furrow is lower, so less drying out.
  • When watering in the furrow, the soil next to it stays dry.  So less weed next to the row.
  • The furrow indicates where the onions have been planted.  No marks needed.


A)# Onion fly and carrot fly 

I used to sow or plant rows of onions (O) next to rows of carrots (C) (or a few rows of beetroots). So OCOCOCO.  This can reduce the attack of your plants by the onion fly or carrot fly. It does not always help that good. You better not plant the sets too early; see chapter B)# Planting time in this tip.

And (found out in 2015) a layer of hay or short grass around and between the onion plants helps well against diseases and insects. See further in this tip at E)# Test: planting date and hay around.


B)# Planting time

(The description below is valid when you don’t put hay or grass on the soil between the onion plants).

Plant a short row of onion sets in early spring. Do not plant too many onions. There is a big risk that they are attacked by the leaf miner fly (curled leaves) or onion fly (maggots in onions, plants die).

So you better plant many (all) onion sets in mid spring or later.

uitjes vroeg

These onions have been planted in early spring (April). Many onion plants suffer from attack by onion flies or miner flies.

uitjes laat

These onion sets have been planted at mid spring (May 15). All plants are healty. From 50 onion plants only 2 died due to attack by the onion fly. In late summer (August) the harvested onions have about the same size as onions from sets planted in early spring (April).


B1) Planting indoors for an early harvest

When you want to harvest big onion bulbs in June (late spring) you can plant onion sets in flower pots with compost early March (late winter). Keep the pots with onion plants indoors for some weeks. Plant the onion plants in the garden soil at the end of March (early spring). Using a flower pot with insertion and strip is useful, (see tip 30 Root ball lifting flower pot     ).

Below a description with photos.

  • Fill a flower pot (with insert and strip) with compost.
  • Use a tea spoon to make a small hole in the compost.
  • Put the onion set in the hole in the compost. Shove compost in the hole around the onion set.
  • Put the flower pots with onion sets indoors at a bright (sunny) spot, temperature 15 to 20 C (59 to 68 F).
  • Regularly water the onions and compost.

  • Let the onions grow bigger indoors.

  • Take the onions out of the pots and plant them (with big root ball) in the garden soil. You can do that at the end of March (end of winter). Plant the onions in a furrow.

  • Lay dry hay around the small onion plants; hay prevents the onions from attacking by onion flies and miner flies. Info at D)# and E)#.

  • Let the onion plants grow bigger.
  • Photos above of April 2, May 1 and June 1 (early, mid and late spring).



1. Under a tunnel

  • You can put some flower pots with onion plants under a tunnel, for example between lettuce plants.
  • Take the onions out of the pots and plant them in the garden soil later.


2. Hay around the plants

When you plant onion sets in the garden soil, you better put a layer of dry hay (or mowed grass) around and between the small onion plants. The plants grow well, the soil does not dry out so easy and the plants suffer less from insects. More info at chapter E)# test: planting date and hay around.


3. Weird shaped onions

Early planted onion sets can give strange (weird) shaped onions, see photo above. The onion sets of these onions were planted on March 16 (winter/spring). Dry hay was put on the soil between and around the small plants. The harvested onions are very big but they have strange outer layers. These onions can be used in the kitchen, but preparing the onions is some harder.

Onion sets planted in early May (mid spring) result in normal looking onions.


B2) Harvest

uienoogst 2014

Harvest of onions from sets and seed in September; more than 10 kilos. The round onions are from seed, sown in April (early-mid spring). The big “flattened” onions are from onion sets, planted in May (mid spring). The small flattened onions in the right box are from sets planted in June (end of spring).


C)# Planting onions

C1) Testing if sets are good

plantuitjes op vochtige grond

Lay dry onion sets on loose moist garden earth. At dry weather spray water over the onion sets. Check if stems and small roots grow from the sets (within 4 to 7 days). Put the onion sets with a stem and roots in the garden soil.

You can do this test when, after planting, many onion sets do not shoot up within 1 or 2 weeks. Possible cause: onion sets are old or have been stored in a moist room. When onion sets are in a moist room, roots will grow to the sets. When put in a dry room again, this growing stops. After putting these dry sets in garden soil, they won’t grow anymore. No new roots, no leaves, no onion.


C2) Procedure for planting onion sets

  • When needed, lay stepping boards on soft soil.
  • Always stand on a lane or on stepping boards to overcome “hardening”of the soil.
  • Fix an elastic string between 2 bamboo sticks. See tip 2) Simple….. nr 4.
  • Or use a nylon cord with knots. See tip 2) Simple…… nr 64.
  • Use a hoe to loose the soil and to make a furrow.

  • Make a  V -shaped furrow using a board. See tip 2) Simple…… nr 2. Or use a garden trowel. Depth of the furrow is about 5 centimeters ( 2 inch). Spread the ground that you “gather” elswhere over the garden.
  • Plant the onion sets. Distance between onion sets about 10 cm (4 inch). Plant depth in the soil: half of the onion size or deeper.
  • Remove the elastic string or cord with knots.
  • Hoe the soil next to the furrow. Earth will fall into the furrow until top of onions is just visible (or just invisible).
  • Remove the stepping boards. Hoe the soil where the boards have been laying on.


D)# Mulching

In tip 22 (Sowing onions) you can read that “mulching” reduces the attack by insects:

When onions are about 10 cm (4 inch) high, you can put organic material on the soil around and between the plants. This is called “mulching”. Put a thin layer of mowed grass or dry hay on the garden soil. There will be less weed plants between the onions and the soil does not dry out so fast. Less onion plants will die or will be attacked by insects. See photo below.


On the photo above there are 2 rows of sown onions next to each other. At the left side of the yellow line, dry grass has been put on the garden soil between the plants. Many sown onions grow there.

At the right side of the yellow line, no grass has been put there. Many sown onion plants died there. After removal of the dead onion plants, onion sets have been planted there.

So mulching next to and between onion plants reduces the attack by insects. This works well at sown onions and at onion sets (see further).


E)# Test: planting date (March 20 to May 1) and hay around.

To find out when onion flies or leaf miner flies lay their eggs on onion plants, the following experiments have been executed:

E1) Planting onion sets, first year:

  • One onion set has been planted in the garden soil each day between March 20 and May 1. This formed a row of 43 onion plants.
  • From the beginning of April on, a thin layer of dry hay has been put around and between the onion plants that were visible. It was found that dry lawn grass on the soil around sown onions showed less attack of flies. Maybe hay (= dried grass) on the soil also helps at onion sets. Hay is for sale in a pet shop and not expensive.

1 mei proef ui

1 juni proef ui

On these photos you see the row with onion plants (between yellow arrows) on May 1 (above) and June 1 (below). Around and between the biggest onion plants there is dry hay.

E2) Big onion plants, first year:

uienrij 1-20

uienrij 21-43

On July 4, the onion plants are bigger. At some plants the leaves curl or lie down (flopping over). These onions are good for harvesting. A few days later all onion plants have been pulled out of the soil. Click on the photos for wide screen view

E3) Harvest, first year:

rij 1-20 oogst


  • At July 8 and July 16, the big onion plants from this experiment have been pulled out of the soil, see 2 photos above. The harvest was 38 big onion plants grown from 43 onion sets. The 38 onions (foliage included) weighed more than 5 kilograms.
  • From 3 onion sets “there were no onion plants left”. The 3 onion sets turned into 3 small onion plants. These small onion plants have died later.
  • At 2 plants the onion bulbs were soft. Maybe they had rotten due to moist hay around the onion.

E4) Test second year:

  • Next year, the test has repeated with 3 rows of onion sets.
  • Three onion sets have been planted next to each other in the garden soil, each day between March 20 and May 1. This formed 3 rows of 43 onion plants each, a total of 129 onion plants.
  • From the beginning of April on, a thin layer of dry hay, dry mowed grass or dry straw has been put around and between the onion plants that were visible.
  • 115 Big onion plants grew from 129 onion sets.

E5) Results and conclusions:

  • Most onion sets grew into big onions; 38 onions out of 43 sets (first year) and 115 onions out of 129 sets (second year). This is about 89 % “yield”.
  • Putting hay around the onion plants works well against attack by onion fly and leaf miner fly. Even during the “risk period” of the leaf miner fly (early spring, March and April).
  • A number of onion plants showed curled leaves (maybe caused by the leaf miner fly), but the big onions looked normal.
  • Maybe the “disappeared” onion plants have been eaten by the maggots of the onion fly.


  • There is little weed between the onion plants. From the layer of hay, small grass plants can grow in the soil. This grass and weed plants are easy to remove (pull out).
  • Under the layer of hay the soil does not dry out so fast. The onion plants grow well.
  • A layer of dry hay around the plants gave more and bigger onions than a layer of straw or mowed grass around the plants. So dry hay works better than grass or straw.


  • Harvest in July; earlier planted onion sets gave bigger (heavier) onions than later planted ones. Reason: onion plants grown from early planted sets had longer time to grow than later planted sets.
  • All 18 onions, planted from sets after April 25 in the second year, had good straight leaves and well-formed bulbs. So from the end of april on, leaf miner flies are not active.


F)# Onions planted early May (mid spring).

In early May, 4 rows of onion sets have been planted in the garden soil. Dry hay has been put between the onion plants in June. Just to find out if this results in good onions. The soil around the onion plants does not dry out so fast thanks to the layer of hay.

F1) Harvest in August.

In early August, the foliage of most onion plants drops. Onions are ready for harvesting then.

plantuitjes na 1 mei, drogen

Pull the onion plants out of the garden soil. Let them dry on the garden soil or on grass (see photo above).

uienoogst plantuitjes na 1 mei

After drying, the leaves and stems have been cut off. Then the onions were laid in the boxes.

Four rows of 42 onion sets each (168 sets in total) resulted in: 160 onions, weighing 14.5 kilogram (without leaves). There were 125 big onions and 35 small onions.

1 juni plantuien

This photo shows the 4 rows with onion plants at June 1. The onion sets planted next to the paving stones (blue arrow) resulted in small onions; less space and less nutrition there.

2 uien mineervlieg plantuitjes na 1 mei

Almost all onions are unattacked and undamaged. Only 2 onions have a “weird bottom side”. They have been attacked by the onion miner fly. More info at tip   4) Insects and diseases of plants     , chapter A2) Leaf-miner fly (on onion plants).

So hay around and between onion plant works well. Also at onion sets planted after May 1.


G)# Harvesting and cutting green leaves

You can harvest onions long before the leaves have dried on the garden soil.

  • Pull onions out of the soil when the leaves are flopping over.

  • Use scissors to cut the biggest part of the leaves.
  • End up with 1 to 2 centimeters (0.5 to 1 inch) of foil.

  • Lay the “cut off” onions in a big cardboard box.
  • Put the box with onions at a dry (sunny) place to let dry.
  • Turn the onions in the box when the upper sides of the onions are dry.

  • After 1 or 2 days all sides of the onions are dry.

  • Use a soft brush to wipe off the dry garden soil.

  • Lay dried onions in an other cardboard box with the “stems up” (or “stems tilt up”).
  • Don’t put too many onions in the box; there must be some free space around each onion.
  • Let the onions dry in this box for about 1 week.

  • Put the dried onions in another cardboard box.
  • Put in many onions with stems up (or stems tilt up).
  • Form only 1 layer of onions.
  • When you put the box slanting, it is easier to put many onions with stems up (or stems tilt up) in the box.

  • Many onions in the box with the stems up or tilt up.


H)# Cutting hay

uien hooi

It can be hard to put “long stem hay” between and around onion plants. Hay with short stems works better.

To shorten it: put some hay in a big flower pot. Use hedge shears to cut the hay into short stems.


I)# Further….

  • At dry weather, water the plants in the furrow 2 times per week (in the evening).
  • When there is no hay or grass on the soil: Next day, loose the soil between the plants using a “hand trident”.  At the same time, remove the weed and reshape the furrow.
  • With hay or grass on the soil: No need for loosing the soil and reshaping the furrow. The hay or grass keeps the furrow in shape. Pull out small weed plants.
  • Once a week, hoe between the rows.

krabbertje E

This entry was posted in onions. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s