Now that autumn (ok, fall) has come to the northern hemisphere, gardeners are turning to bedding down their gardens for winter and planning for the spring. We know this because there has been a flurry of questions and seed orders are picking up again too. As well as answering questions by email I’m posting the information on the blog so that it’s available to all. If you have tips to offer, remedies to share or stories to tell, please feel free to comment or email me directly and so help build this resource. Names may be changed, or items remain anonymous, to protect the innocent.
I’ll try to keep this going every week. So, this week:
Can I grow delphiniums in heavy, water-logged clay?
A couple of years ago Syd, in zone 5 to 6, had trouble growing his plants in soil that “may get water logged from heavy rains, or snowmelt in the winter. It then takes awhile to dry out. If I dig a 12 inch hole and it rains heavily, the hole fills with water and takes days to dry out”. It can be difficult in summer too.
We had a chat about this and I suggest planting the delphiniums in raised beds with
their roots and potting mix only half in the ground. “Then add composted manure
or other light mulch to cover the root ball well. You could do this to the extent
that the planted plant looks like it is on a hole in the mulch. The delph will love the moist
clay but many of the roots will also be growing in the mulch which will be well
drained and full of oxygen and minerals. Once the mulch rots away replace with new. I will lay a pound to a penny that this solves the problem”.
Syd wrote back this week to say that it had, to a large degree, worked. If you have ground prone to water-logging then a similar strategy may help. I discovered this myself when one, very wet winter I simply dug up the delphiniums (loud sucking noise) in a similarly waterlogged garden, left them lying on the ground and promptly forgot about them until the spring, by which time they had grown new roots in the soil beneath and were well on the way to flowering. It worked a treat. Don’t worry about them getting too dry in the winter – they will be dormant and completely unconcerned, growing new roots when they need them.
Take care with insecticides, especially “systemics” on young seedlings.
Clouding the issue with Syd’s delphiniums was the fact that he was battling with compost fly in the propagation house. Not only do the larvae chew on the roots of young seedlings, the flies also spread damping off diseases. Syd had attacked the flies, a little too enthusiastically, with a systemic, granular insecticide. He killed them alright but nearly killed the seedlings too. They were looking pale and disinterested but when planted out recovered quite well.
There are a few issues here. Plants that have fought off damping off, or generally had a difficult start to life, seldom grow away as vigorously as they should. That’s one of the reasons Syd’s original plants didn’t grow well in the garden. Although the batch drenched with insecticide (to stop the compost fly and damping off) almost died, they grew away again when planted out, still free of the damping off pathogens. However, compost fly can be dealt with less severely and more safely. If compost fly is a problem I'd spray or, preferably, drench the soil with Bacillus Thuringiensis (BT) at the time of sowing. These bacteria attack the larvae of the compost fly and don’t damage the seedlings.
Once the seedlings are well emerged choose a warm, airy day (if you have any then) and water them again with the BT.
Thuricide, containing BT may also be used to control other caterpillars and it won’t harm beneficial insects. One source of supply is here:
It should be available at most garden centres.
How do I avoid “Damping Off”
This is a regular. Firstly, take care of your hygiene and be mindful of things that may spread disease (like Syd’s compost fly, or excessive water). Avoid overwatering seedlings and don’t water or spray overhead in conditions that will result in the seedlings being damp for more than an hour or so. You can find plenty of information about the control of damping off on our web site, here:
If you can’t find this at a garden centre then try your local organic gardening club. I’m trying to find a northern hemisphere source on the Internet, but with little success. Can anyone help?
In New Zealand “Dalton’s” seed raising mix contains trichoderma fungus - and is simply wonderful.
That’s all for now.