John's advice after 25 years growing at Ashbrook allotments
Onions
Although it is possible to plant sets in the autumn in order to obtain a summer crop I find they do not seem to keep as well as spring plantings. The following notes therefore apply to spring plantings.
When growing spring planted onions it is worth remembering a few of their characteristics.
There are several ways of growing onions for the kitchen.
The most common and easiest way is to grow from sets planted directly into prepared ground during March and April; trim the wispy top without cutting into the growing tip and plant the sets with the tip just showing in rows about 30cm (12”) between sets and 30 to 38cm (12” to 15”) between rows. These distances allow the plant adequate space to develop and give enough room to use a dutch hoe. Keep an eye on the rows and replant any that are pulled up as soon as possible before any emerging roots dry out, some years this is a real problem, jackdaws are the main culprits, this can be prevented by putting netting over the rows until the plants are established.
In a favourable season good results can be achieved by planting sets as above however over the years particularly when we have experienced poor growing conditions I have ended up with a disappointing crop of very small onions. If this happens you might like to consider a slightly different method of starting your off your onion sets.
Nowadays I plant my sets in 4” pots in good quality multipurpose compost in the greenhouse about mid February or in March using 3” pots, I find cell trays too root restrictive. They are then grown on in the greenhouse or cold frame and planted out as the soil starts warming about the third week of April and spaced as above. This way up to eight weeks of growth and a plant with a large root system and quite a few leaves has been developed in sheltered conditions; ultimately if given space to grow a good sized onion can be produced.
A third way of starting off your onions is by sowing seed. At Ashbrook I have never produced decent onions from seed sown directly in the ground; it might be possible in warmer areas. However seed sown indoors in early January, mine are started off on the kitchen window cill, transplanted to 3” pots, grown on in a greenhouse and planted out during the second half of April and spaced as above can give very good results.
The bulbs swell during July and if an onion is needed immediately for the kitchen they can be used straight out of the plot without ripening. However if they are to keep through the winter they do need thorough ripening and a well ventilated greenhouse or cold frame is invaluable for this. If the bulbs get a surge of late rainwater they do not keep well, can develop split skins and be prone to mildew so if wet weather is forecast I lift them out of the ground quickly. Generally I lift towards the end of July or early August and lay the bulbs flat or tilted at an angle on a green house shelf protected from rain for about four weeks to ensure they are dry, ripe and ready for storage. When nearly ripe trim the tops and leave upside down to continue ripening for a couple more weeks. Although many like to string up their onions I have never found this a good method for long term storage. However stored upside down in plastic mesh mushroom boxes (to ensure any residual moisture can drain and evaporate) kept in a cold but frost free shed they should keep well until the following spring. During the following April as any remaining bulbs come start to come back to life peel off any loose skin and put them in the salad drawer of the fridge where they keep till the middle of June by which time fresh shallots are available and the next year’s onion crop is not far away. By storing this way we have not bought any onions for many years.
Onion White Rot is becoming a real problem around the country particularly on allotments; it is normally initially imported via infected bulbs then spread via tools and muddy boots, once in the ground it can take many years to eradicate. With an isolated outbreak any infected bulbs along with a spit of surrounding soil is best bagged up promptly and destroyed or disposed of away from the site where it will cause no damage. Drenching the hole with Jeyes Fluid seems to prevent it spreading further; infected bulbs should not be put on the compost heap. It is very noticeable that gardeners who retain their own clean shallot sets and who grow their onions from seed therefore not importing any sets whatsoever have the least problem.
In many areas leek moth and allium leaf miner are causing significant damage.
Leek moth tends to mainly affect leeks, being a moth the larvae is a small caterpillar.
Allium leaf miner is far more destructive as it damages all alliums e.g. leeks, onions, shallots, chives, garlic and ornamentals, being a fly the larvae is a maggot.
The damage with both pests is similar, leaves appear slug damaged and the larvae found within the crop cause further damage often leading to botrytis.
The larvae overwinter as pupae either in the soil or within old crops and foliage and hatch out in the spring. Any crops found with these pests should not be put on compost heaps.
Leek moth is definitely at Ashbrook but I have not yet heard of it affecting our onions. Allium leaf miner might not have arrived yet but we know is affecting allium crops nearby. The most effective solution for both pests will be to cover crops with environmesh from April until October.
Sets
Centurion is a particularly good onion that bulbs early and stores well, my own preference.
Fen Globe, Stuttgater Giant and Sturon also give good results and store well.
Santana is another good keeper with downy mildew resistance.
Red Baron is a very popular red onion in the kitchen however if grown from sets can be prone to bolting. If you have this problem either plant sets when the ground starts to warm up say about the third week in April. Alternatively consider growing from seed germinated indoors in January, grown on in pots in the greenhouse and planted out late April, I have found seed sown plants grown this way a very good method to grow Red Baron.
When growing spring planted onions it is worth remembering a few of their characteristics.
- Firstly, their growth is influenced by day length; they form leaves as the days lengthen and the bulbs swell during July as the days start to shorten.
- Secondly, the ultimate size of an onion is determined by the number of leaves it produces, each internal ring represented by a leaf.
- Thirdly, originating from warmer climes than ours they are not keen on the cold and wet conditions we often get on our site during early spring, indeed a check to growth can make them bolt (run to seed).
There are several ways of growing onions for the kitchen.
The most common and easiest way is to grow from sets planted directly into prepared ground during March and April; trim the wispy top without cutting into the growing tip and plant the sets with the tip just showing in rows about 30cm (12”) between sets and 30 to 38cm (12” to 15”) between rows. These distances allow the plant adequate space to develop and give enough room to use a dutch hoe. Keep an eye on the rows and replant any that are pulled up as soon as possible before any emerging roots dry out, some years this is a real problem, jackdaws are the main culprits, this can be prevented by putting netting over the rows until the plants are established.
In a favourable season good results can be achieved by planting sets as above however over the years particularly when we have experienced poor growing conditions I have ended up with a disappointing crop of very small onions. If this happens you might like to consider a slightly different method of starting your off your onion sets.
Nowadays I plant my sets in 4” pots in good quality multipurpose compost in the greenhouse about mid February or in March using 3” pots, I find cell trays too root restrictive. They are then grown on in the greenhouse or cold frame and planted out as the soil starts warming about the third week of April and spaced as above. This way up to eight weeks of growth and a plant with a large root system and quite a few leaves has been developed in sheltered conditions; ultimately if given space to grow a good sized onion can be produced.
A third way of starting off your onions is by sowing seed. At Ashbrook I have never produced decent onions from seed sown directly in the ground; it might be possible in warmer areas. However seed sown indoors in early January, mine are started off on the kitchen window cill, transplanted to 3” pots, grown on in a greenhouse and planted out during the second half of April and spaced as above can give very good results.
The bulbs swell during July and if an onion is needed immediately for the kitchen they can be used straight out of the plot without ripening. However if they are to keep through the winter they do need thorough ripening and a well ventilated greenhouse or cold frame is invaluable for this. If the bulbs get a surge of late rainwater they do not keep well, can develop split skins and be prone to mildew so if wet weather is forecast I lift them out of the ground quickly. Generally I lift towards the end of July or early August and lay the bulbs flat or tilted at an angle on a green house shelf protected from rain for about four weeks to ensure they are dry, ripe and ready for storage. When nearly ripe trim the tops and leave upside down to continue ripening for a couple more weeks. Although many like to string up their onions I have never found this a good method for long term storage. However stored upside down in plastic mesh mushroom boxes (to ensure any residual moisture can drain and evaporate) kept in a cold but frost free shed they should keep well until the following spring. During the following April as any remaining bulbs come start to come back to life peel off any loose skin and put them in the salad drawer of the fridge where they keep till the middle of June by which time fresh shallots are available and the next year’s onion crop is not far away. By storing this way we have not bought any onions for many years.
Onion White Rot is becoming a real problem around the country particularly on allotments; it is normally initially imported via infected bulbs then spread via tools and muddy boots, once in the ground it can take many years to eradicate. With an isolated outbreak any infected bulbs along with a spit of surrounding soil is best bagged up promptly and destroyed or disposed of away from the site where it will cause no damage. Drenching the hole with Jeyes Fluid seems to prevent it spreading further; infected bulbs should not be put on the compost heap. It is very noticeable that gardeners who retain their own clean shallot sets and who grow their onions from seed therefore not importing any sets whatsoever have the least problem.
In many areas leek moth and allium leaf miner are causing significant damage.
Leek moth tends to mainly affect leeks, being a moth the larvae is a small caterpillar.
Allium leaf miner is far more destructive as it damages all alliums e.g. leeks, onions, shallots, chives, garlic and ornamentals, being a fly the larvae is a maggot.
The damage with both pests is similar, leaves appear slug damaged and the larvae found within the crop cause further damage often leading to botrytis.
The larvae overwinter as pupae either in the soil or within old crops and foliage and hatch out in the spring. Any crops found with these pests should not be put on compost heaps.
Leek moth is definitely at Ashbrook but I have not yet heard of it affecting our onions. Allium leaf miner might not have arrived yet but we know is affecting allium crops nearby. The most effective solution for both pests will be to cover crops with environmesh from April until October.
Sets
Centurion is a particularly good onion that bulbs early and stores well, my own preference.
Fen Globe, Stuttgater Giant and Sturon also give good results and store well.
Santana is another good keeper with downy mildew resistance.
Red Baron is a very popular red onion in the kitchen however if grown from sets can be prone to bolting. If you have this problem either plant sets when the ground starts to warm up say about the third week in April. Alternatively consider growing from seed germinated indoors in January, grown on in pots in the greenhouse and planted out late April, I have found seed sown plants grown this way a very good method to grow Red Baron.