down to earth: Liming for crop health
Spring is the busiest time in the garden, so hopefully you’re well rested and amping to get stuck in. Often mentioned is the act of liming. You may ask what all the fuss is about. Have you noticed any of the following symptoms in your garden?
Flat weeds (eg dandelions, plaintain) and moss in the lawn.
Variable-sized clovers in grass/pasture/lawn.
Poor worm life in soil.
Poor growth in alkaline-loving crops such as spinach, beets, brassicas, celery and cucumber.
To know for sure, it’s best to get your soil pH tested (pH is a measure of a soil’s acidity). Under acid conditions many soil nutrients become unavailable (eg phosphorus and molybdenum). The ideal pH for most crops is between 6.0 and 6.8, a slightly acid soil.
Soil will become acidic with application of chemical fertilisers, organic matter, and influence from nearby native regeneration (as forests ecosystems are acidic). Most soils become acidic over time, why is why growers apply lime.
Lime is made of calcium (Ca) carbonate (CO3). Calcium is a strong cation that helps nutrients become available in the soil. There are different kinds of lime, and each has its use. Ag Lime is the main source of calcium and widely used to raise pH. Dolomite has calcium and magnesium (Mg), another cation, so if Mg is needed then you get two for one. But if your soil has enough then dolomite can oversupply Mg, limiting other nutrients. Crop fine lime (ground to 150 microns) will act more quickly than coarse limes. Lime flour (ground to less than 20 microns) is usually an animal remedy; however when applied to the soil in solution at smaller rates it will have an immediate effect on pH and benefit soil organisms, although its affect on pH is short-lived.
How much lime you need to apply depends on your pH and soil type. Typically heavy clay and soils rich inorganic matter (eg peaty) will need more lime to alter pH than sandy soils. This is due to their “buffering capacity” (or CEC=cation exchange capacity as seen on soil tests) which relates to a soil’s ability to resist pH change. As a guide, a clay soil may require 300 to 450g of quality lime per square metre to raise its pH from 5.5 to 6.5, while a sandy soil would require 150 to 200g of lime per square metre for the same pH change. On a larger scale, on average mineral soils about 1 tonne/ha of surface-applied lime is required to shift the pH by 0.1 unit.
Rainfall needs to be considered too, as lime is washed through the soil profile more quickly in high rainfall areas.
It’s better to apply lime here twice a year rather than all at once, as in autumn and/or early spring. Broadcast by hand over small areas or with a spreader over larger areas. Lime is best mixed into the soil with a fork or cultivator and then left for a while before planting to allow it to react. If you use a green manure crop as part of your rotation, then apply lime when the green manure is turned under. It is also possible to topdress with lime at other times of the year without damaging growing crops, but it will take longer for the lime to raise the pH.
Liming has a beneficial effect on some soil fauna, like earthworms and nitrogen-fixing bacteria, so it improves soil’s structure and moisture retention, promoting better crops.
Fruit care
Plant subtropicals. Stake. Protect from wind and animals.
Prune newly planted fruit trees to chosen shape (eg vase for stonefruit and centre leader for pipfruit).
Plant comfrey under fruit trees at drip line or 1.5m from trunk.
Sow understorey plants under fruit trees or on edges to encourage beneficial insects and improve soil health (see Kings Seeds for mixes).
Mulch fruits with woody compost and manures (especially citrus and peaches).
Plant strawberries.
Prune citrus when harvesting. Spray with all-purpose oil for scale insect.
Spray everything with diluted seaweed solution. Spray lime sulphur (after blossoming) on fruit trees vs
peach leaf curl, black spot, powdery mildew, as well as scale, mites and borers.
Herb care
Transplant rooted cuttings from last year.
Weed herb beds in preparation for sowing annual herbs like parsley.
Sow herb seed indoors.
Vegetable care
Make loads of compost as you complete bed preparations.
Begin main spring sowings indoors, especially tomatoes, peppers and eggplants.
Dig in remaining green manures or cut and cover with black plastic for mid-spring plantings.
Plant early potatoes into organic-matter-rich soil and protect from frost.
Prepare beds for hot crops (eg tomatoes, cucumbers, etc): add lots of compost, blood and bone and organic compound NZ fert.
Continue preparing seedbeds for sowings of root crops.
Sow/plant beneficial flowers, eg phacelia.
Hothouse: Main sowings into punnets/trays. Watch for snails. Make indoor compost to raise temperature. Plant early tomatoes and cucumbers into rich beds.
For transplanting: All seeds 21 September. Leafy greens (spinach, spinach beet, silverbeet/chard, lettuce, endive, kohlrabi, cabbages). Tomatoes, peppers, eggplants (bottom heat), cucumbers, zucchini and pumpkins. Broccoli, cauliflower (also 13 Sept). Flowers, eg delphinium.
Sow direct: All seeds 21 September. Mesclun salad, spring onions. Peas and French beans (cover) (also 7-8 Sept). Radish, carrots, beetroot (cover), parsnip, kohlrabi, turnips, swede (also 10-11 Sept). Flowers, eg snapdragon.
Plant: Salad greens, spinach, broccoli, cauliflower and cabbages. Early potatoes in frost-free areas. Onions. Flowers, eg tip cuttings of carnations into sand under cover.
General garden care
Mulch perennial gardens with bark.
Mulch-mow lawn and lime.
Collect seaweed/seagrass.
Plant comfrey near compost bins and set up liquid fertiliser drums for manures, seaweed/seagrass, comfrey/weeds (nb: I put in my hard-to-compost weeds like dock, convolvulus, etc).
Sol Morgan, GroWise Consultancy
