This is the third part of a series on crop planning for seed production. Seed production planning part 2 covered calculating how much seed to harvest to meet your farm and marketing demands.
The next step is determining how many plants you need to grow to produce the amount of seed you need. We’ll look at the basic math to calculate how much to plant and two examples.
CALCULATING HOW MUCH TO GROW
This is the basic equation:
Harvest Targets x Safety Factor ÷ Yield = Bed Length to Plant
Harvest Targets: This was calculated in Seed Production Planning part 2.
Safety Factors: Weather, pests, diseases, and weeds can dramatically alter what you can expect to harvest. Seed yields are more variable than vegetable yields. It’s good to target growing 25% to 75% more seed than you need to compensate for the potential losses.
Yield: The amount of seed you can expect to harvest on average from a certain number of plants or area of crop. Last spring I wrote a blog on seed yields that goes further into the subject.
Here is an updated chart of some of our seed yields at Tourne-Sol farm.
| Crop | Rows/Bed | Inrow spacing | grams/bedft* |
| Beans | bush – 2 pole – 1 | 6″-12″ | 75-100g |
| Beets/Chard | 2 | 12″ | 100g |
| Brassicas | 2 or 3 | 12″-18″ | 25-100g |
| Cucurbits | 1 | 24″ | 25-100g |
| Lettuce** | 3 | 12″ | 10-28g |
| Onions | 3 | 12″ | 25-50g |
| Peas | bush – 2 pole – 1 | 6″ | 50-75g |
| Solanacea | 1 or 2 | 12″-24″ | 3-10g |
* A bedft is a one foot long slice of your growing bed.
** Our lettuce yields are lower than what is possible in drier climates.
EXAMPLE 1 – HOW MUCH TATSOI SHOULD I GROW?
In Seed Production Planning part 2 we estimated 6720g of Tatsoi seed would meet our hypothetical farm and marketing needs. From previous experience I know my Tatsoi seed yields about 50g/bedft but that the yield can vary greatly from year to year.
Harvest Targets x Safety Factor ÷ Yield = Bed Length to Plant
6720g x 1,5 ÷ 50g/bedft = 201 bedft
If I grow 200 bedft, I should be able to meet my Tatsoi seed needs. If the weather cooperates and I harvest before much seed shatters, I could potentially harvest much more seed than I need.
EXAMPLE 2 – HOW MUCH JAUNE FLAMMÉE TOMATO SHOULD I GROW?
Harvest Targets: 321g would meet our hypothetical farm and marketing seed needs.
Yield: I usually get about 7g/bedft of seed from small to medium-sized tomatoes like Jaune Flammée.
SF: On our farm tomato yields don’t vary as much as brassica greens. I’ll only use a 1.25 SF.
321g x 1,25 ÷ 7g/bedft = 57 bedft
I should meet my Jaune Flammée seed needs if I grow 60 bedft of plants.
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In my next post, I’ll tackle when to plant seed crops to make sure you can harvest on time. And later, I’ll cover some seed crop rotation basics.
I also plan on posting some of what we’ve been doing during this rainy spring.
Hope it’s as sunny as you would like it to be wherever your skies are …
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