Garden Vegetables - How To Know Exactly When To Plant And Harvest Them

You don't have to rely upon the vague seed harvesting times predicted on seed packets. They're based upon an 'average' garden. No gardener's soil, garden layout or micro-climate are exactly 'average'.

Solution? Try this clever gardening tip to grow more vegetables. Measure the Heat Units (HUs)!

HUs are one way that commercial growers know exactly when to roll out the harvesting machines. Do they read seed packets? No. We can easily use their method too. It's simply a matter of keeping a record, year to year, of how much thermal energy a given crop has received in a certain plot. These records will be different for every garden and every crop.

Keeping a garden log is the first step

The first thing you do is set a Base Temperature and thereafter take note of the average temperatures each day. If you grow plants that flourish in a cool climate, like cabbages and lettuce, make your Base Temperature 40ºF. For warm weather crops - like tomatoes, beans, squash, sweet corn - set it at 55oF.

This temperature is just an arbitrary point of reference. But you must keep it constant in all your measurements so that you can make sensible comparisons between the plants. You can now work out your Heat Units.

On the day you sow a crop outdoors, record the daily high temperature and the daily low. Add them and divide them in half. Now you have an average temperature. Subtract the base temperature from this number to obtain the HUs for that particular day.

How to know when to pick organic garden vegetables

Let's imagine you have planted tomatoes in early summer. On day one the temperature is 70ºF at its height and 60ºF at its lowest point. This gives an average temperature for the day of 65ºF. Take away the Base Temperature 55ºF you have determined for tomatoes and you're left with 10. This is the number of HUs.

Many long-season plants like cabbages and beefsteak tomatoes may want more than 1000 Heat Units to mature fully. Early tomatoes will need fewer than 600 HUs. You will know in advance from your own logbook. It will reveal exactly the Heat Units needed by each species and variety.

For instance, you could plant Siberian tomatoes - very early - just after the last frost day in your region. You'll know from your logbook that Siberian requires only 480 Heat Units. That's when the fruit will be ripe to pick.

Another virtue of this method is that you can plan profitably for succession planting. When you know from experience that your spinach will be ready to crop around 30th May you can have transplants of outdoor tomatoes ready to replace them at once. That's a lot better than consulting textbook dates, which were not written for your garden.

A lazy gardening way to check garden temperatures

Do you need to rush out each day to check the temperature? No! Hang an electronic high-low thermometer outdoors that you can read from a lounge chair in your house, using bird watchers' binoculars. Then set up an automatic watering system. And relax. You know you won't have to take even one step into the cruel outdoors to harvest your first tomatoes until 490 HUs have been achieved. (That's probably around 29th July in a temperate northern zone.)

Your Heat Units will be different even from your neighbors'. Yet despite even wide temperature fluctuations, month by month, in your garden you can be fairly sure of when every crop will be ready - just by doing the math. That's a great benefit for every busy gardener!