A BT Convert


So this year, I decided to try something new in the brassica bed.  Instead of the usual netting, I decided to try using BT (Bacillus thuringiensis) to keep the cabbage worms at bay.

So far, I've harvested over 11 lbs. of Aspabroc from the 4 plants I'm growing

This was not so much brought about by my desire to try something new, but rather the fact that the netting for this bed had torn.  Both the broccoli and onions have special netting as they are too tall for the standard size.  In both cases, I have to sew two lengths of netting together to get the required height.

This spring, I realized that one of the nets was torn and would require serious patching (i.e. sewing).  The onions took priority so they received the intact netting.  The brassica bed (which this season holds broccoli and some newly sown kohlrabi & cabbage) was covered with the smaller netting until the broccoli grew too large, at which point I removed the netting.  I then waited until I saw cabbage worm activity to apply BT, an organic solution which only affects caterpillars.

You can see how much larger the broccoli is than
the black hoops that accommodate the smaller netting

I have never used BT before so this was all new to me.  Firstly, the instructions on the bottle indicated that, once mixed with water, the solution had to be applied within 24 hours.  This meant that I couldn't use my typical spray bottle that I fill and just have sitting around to use whenever I needed it.  I would have to make a fresh batch each time.  Luckily, I found a small travel size spray bottle that holds exactly 3 tbsp. of liquid - more than enough to spray 4 broccoli plants.  I only needed to add 1/8 tsp. of the concentrate so the 100 ml bottle of BT should last quite a while.

BT with my mini-spray bottle

I sprayed on July 7th, once I noticed cabbage white butterflies fluttering around the broccoli & saw a few tiny cabbageworms on the leaves.  I made sure to spray the undersides of the leaves, as that's usually where I see the worms and that's also an area of the leaf that is protected from both rain and sunshine which I've read degrades BT.   Once the caterpillars have some of the bacteria in their system, they stop feeding and eventually die.

A tiny side shoot develops beside one that I've already harvested.

And that was that.  I thought I would have to re-apply more frequently (with Aspabroc, and many other broccoli varieties, the side shoots provide the true bounty all summer long) but I checked the leaves several times over the next few weeks and didn't find any worms.  It was amazing!  What was also amazing was not having to deal with netting when weeding or harvesting.  Pure luxury.

From my recent experience with some kohlrabi and cabbage seedlings, I'll likely still use netting while the seedlings are small.  But once they are "teenagers", I'll be switching over to BT which will make my life that much easier.

Update:  I've been using BT on brassicas now for a couple of years and it works quite well.  While BT is considered an 'organic' option, I still try to limit my use of it & can often get away with only applying it once in July (applying to the underside of the leaves, I feel, is key).  Do be aware that BT does not discriminate - it works on ALL caterpillars - so please be especially careful when using it.  Don't use it on a windy day and be cautious with overspray onto other plants that may host caterpillars that you DO want such as dill, fennel or milkweed.


  1. Hello there Margaret ! .. This is one of the reasons I never got into vegetables .. they need so much attention and work .. I ma way too lazy ? LOL
    But even the colours of them are eye catching .. that blue green is beautiful!
    Good luck with the battle .. I face that with lily beetles .. I hope to get neem oil for next year and really make a dent in them !
    PS .. those little yellow flowers next to the raised bed are so pretty !
    Your beds are so neat and tidy too.

    1. The yellow flowers are self-sown calendula - I just let them come up where they may & pull those that get in the way!

  2. That was definitely was worth the effort! Another garden blogger friend of mine recommended BT when I had problem with tent worms on an ornamental plant - the advice came to late in that case but, with your testimonial as well, it's something I'll try the next time I have a problem on that order.

  3. What a great result. It sounds much easier than struggling with netting too, and it'll make weeding much easier too without having to struggle beneath netting.

  4. I’m not sure this is available here not we would need to net anyway as protection from wood pigeons.

  5. I've had good luck using BT for years now. I mix it with neem oil, which kills any live caterpillars and seems to have a synergistic effect. Both are safe to humans.

  6. Organic gardening is not for the faint of heart. Scouting and finding the right organic spray for the 'pest' is key. Glad you found a successful solution.

  7. Glad this worked for you. I have never tried it, but have considered it.


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