Lettuce be sweet, please

Tessa from Blunders with shoots, blossoms 'n roots sent me this Question about bitter Lettuce via my Gardening question and Contact widget.

If after reading all the to and fro between Tessa and I you have anything to add then Tessa has said she would love to here from you. You can either leave a comment here or go to Tessa's Blog at Blunders with shoots, blossoms 'n roots


Thursday, 19 February 2009
Name: Tessa
Subject: Bitter lettuce
Message: Hi, Well, I certainly hope you can help me- or I might go crazy! Would you happen to know what makes lettuce go bitter- I'm growing it in winter when it couldn't possibly be too hot to cause it to bolt. I've been careful with my watering too. Even one of the varieties that I've never had a problem with has sometimes been bitter! Oh, it's driving me nuts! It's my staple, year round. I hope you can help! And now that I'm done...happy gardening! Tessa

My response was as follows:-

Hi Tessa, thanks for the question and sorry for taking so long to reply, I've had a major attack of procrastination this last week.

So bitter lettuce huh?

First off I need to ask you a few questions.

What was your soil prep prior to planting?

And do you know roughly know what the ph of your soil is.

And did you buy seedlings and if so what size were they at planting.

Also did they receive full sun all day?

I am looking for what could have caused bitterness in your lettuce and will explain fully what the questions are for when I get your reply.

To which Tessa replied:-

Hi Stewart,

Sorry, your email got stuck in spam. Well, my soil is pretty good.
The lettuce was sown late summer for winter harvesting, along with corn salad and spinach. All the other varieties are not bitter- and this one is usually not bitter.
My soil in the cold frame is good. Loose, loamy, and I put compost in there after each crop is harvested- just a layer on the no-dig surface. I also add greensand, rock phos, and some other amendments in a blend.
I have run into this problem before, occasionally, and it's driving me nuts, because I can't seem to narrow down what the problem could be. Watering is regular, but I go by if it needs it not a 'schedule'. Winter watering is at a mimnimum, of course, as it is not needed too much. I hope you can help. Luckily for me the one that is bitter is also one that I need to figure out how to collect the seeds as it is no longer offered by Johnny's. I do have a whole other flat, however.

Thanks,

Tessa

On Tue, Feb 24, 2009 at 4:30 PM, Stewart wrote:

Hi Tessa, Two things I picked up from your reply. First is lettuce like to be grown quickly. I see you use compost and add greensand, rock phos, and some other amendments in a blend which is all good. I'm courious about your nitrogen though. Being a leafy crop lettuce need a good supply of nitrogen. Here, I use blood and bone in the soil prep and then weekly applications of half strength liquid fish emulsion fertilizer. It's possible your nitrogen could be a bit low.

Second you mentioned you like to transplant them a few times. Lettuce don't like any check in growth and transplanting can cause this. You mentioned you direct sow your lettuce which is what I do and recommend so as to keep them growing without any check in growth.

My question regarding soil pH was to find out if your soil is slightly acid of alkaline, either of which can effect bitterness and growth. Your soil pH needs to be around 6.0 to 6.7.(slightly acid to netural)

Anyhow that's what I've got for now. If you have any questions or feedback I'm happy to hear from you and I hope some of this helps

Cheers

Stewart.

And finally:-

Thanks Stewart, I do put blood meal in the fert. mix. Our soils are acid- I lime somewhat to counter that. Maybe more is needed- however, getting too much can cause long term problems here too- so I may be a bit too cautious. I have found that transplanting lettuce seems to stimulate good root growth (also have read this, in Colman book), but I really think it depends on the time of year. If light levels (such as fall and winter) are low, and soil temps are cool, most crops can't take up nutrients. So, fertilizing in winter can cause nitrogen build up. It could be that they didn't get big enough in fall for the winter harvest. Starting them just before the light levels dip and getting them to a size just under full maturity, is key for winter harvest. They just sit and wait until you either harvest, or warmer weather and light levels return. Timing is everything ;) and my timing was off, I think! I think maybe I'll do a soil test just in the cold frame this year- so I can rule that out, and come late summer, plan a little more carefully so the timing is better...assuming the weather cooperates!! Thanks so much for your help- you gave me some things to check and consider. It's nice to know I have another knowledgeable gardener to turn to! Take Care,

Tessa
I also made a final comment to Tessa asking permission to use our exchange and added that I thought her lettuce are far more spoilt then mine. I had thought about timing but as I can grow lettuce all through winter here I was unsure how that would effect yours. I'm interested about your comments about transplanting stimulating root growth, I'll experiment with that and see what happens.

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