SEEDS AND SOIL TEM­PER­A­TURES

The Wellingtonian - - Front Page -

There’s an old say­ing that the time to plant seeds is when you can com­fort­ably sit on the ground with a bare bot­tom. I pre­fer to use a soil ther­mome­ter in­stead of shock­ing my neigh­bours! I have a nifty, du­alpur­pose one that shows the soil and air tem­per­a­tures at the same time. In gen­eral, the soil in wooden raised beds is warmer than gar­den beds, and metal and ter­ra­cotta pots are warmer still. For ex­am­ple, one af­ter­noon, when the air tem­per­a­ture was 15 de­grees Cel­sius; the soil in a wooden raised bed was 12C; the soil in an old cop­per in full sun was 13C, but heavy, wa­ter­logged clay gar­den soil only reached 10C.

Mois­ture and soil con­sis­tency af­fect the tem­per­a­ture too. Light, aer­ated pot­ting mix that’s well drained warms up much faster than dense, wa­ter­logged clay. In­ter­est­ingly, the soil tem­per­a­ture is much more sta­ble than the air tem­per­a­ture. Early the fol­low­ing morn­ing, the air tem­per­a­ture was 11C, the raised bed and the cop­per were 12C and the clay soil was still at 10C. So why does it mat­ter? Seeds need spe­cific tem­per­a­tures for ger­mi­na­tion.

You’ll have much bet­ter re­sults if you wait un­til the tem­per­a­ture is in the right range be­fore sow­ing spring and sum­mer crops. Beans, for ex­am­ple, need soil tem­per­a­tures of 18-25C for re­li­able ger­mi­na­tion. There are some soil warm­ing tech­niques to speed things up. Try cov­er­ing a gar­den bed with a cloche or a sheet of plas­tic to warm up the soil for a cou­ple of weeks be­fore plant­ing. I’m us­ing the poly­car­bon­ate sheets to warm up my sog­gi­est gar­den bed. where Vic­to­rian walled gar­dens are metic­u­lous recre­ated, they use marked mea­sur­ing tapes to line up the veg­eta­bles in reg­i­men­tal ranks.i don’t bother to use a ruler as I went ‘‘dig­i­tal’’ long ago. Noth­ing elec­tronic, just my fin­gers, thumbs and whole gum­booted foot. My handspan is 18cm so I al­low a tad over a handspan be­tween seedlings that need to be 20cm apart. The width of my hand in­clud­ing the thumb is 10cm and that of my in­dex fin­ger is 1cm. From the tip of my in­dex fin­ger to the sec­ond joint is 5cm and my gum­boot is 27cm long. Learn the mea­sure­ments of your own hands and feet as a guide when sow­ing seeds or thin­ning out seedlings. When di­lut­ing fer­tiliser, it’s handy to know that a stan­dard plas­tic bucket is 10 litres. For me, one hand­ful is 75g, so I can work out how many hand­fuls of fer­tiliser or gyp­sum to spread.

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