Bio-intensive Approach to Small-scale Household Food Production (IIRR, 1993, 180 p.) Crop management Crop planning Using the fenceline for planting annual and perennial crops Companion plant guide chart Vegetables that can be harvested in less than a month Shade-tolerant vegetables Drought-resistant vegetables Solarization: A weed control technique using sunlight Watering Mulching The role of organic mulches Some tropical materials for use as mulch Gardening in dry environments Water-saving ideas for gardens during dry season Growing vegetables in saline areas Lead in urban gardens

Bio-intensive Approach to Small-scale Household Food Production (IIRR, 1993, 180 p.)

Crop management

Crop planning

Crop planning considers what, when, where and which plants to grow in relation to their requirements for space, sunshine, water, maturation, season of planting and tolerance for each other.

For a garden to give the maximum yield for the family, it should be kept planted all the time. Good planning is necessary.

Important Considerations in Crop Planning

1. Diversification

Grow different kinds of vegetables, trees and other plants in one area. Each plot must contain at least one of each of the following crop categories: leafy, legume, tuberous and fruitbearing vegetables. In this way, the nutritional needs of the family are being met. By growing a diversity of vegetables of different durations, the family is assured of the availability of vegetables throughout the year. This practice is also one way of checking pest outbreaks and certain intercrops serve the additional purpose of being insect repellents.

Rotation of Each Crop Within Each Bed

Bed	Planting season
Subdivision	First	Second	Third	Fourth
1	Leaf	Fruit	Root	Legume
2	Fruit	Leaf	Legume	Root
3	Root	Legume	Leaf	Fruit
4	Legume	Root	Fruit	Leaf

2. Crop Rotation

Different plants have varying' rooting depths and so extract nutrients and moisture from different points of the soil profile. The cultivation of different plants in the same part of the bed from season to season does not overburden the soil. Also, each kind of plant takes away something from the soil, but also gives something back. By rotating the plants from one part of the bed to another, the land is allowed to rest from one kind of plant and the soil gets richer from the other plant that was put in its place. Crop rotation enables the land to "rest" without keeping it idle. Follow heavy feeders with heavy givers and then light feeders.

3. Intensive Planting

Use every bit of the area as many months of the year as possible. Close spacing is recommended to prevent the growth of weeds and reduce the direct exposure of the soil to sunlight, thereby reducing moisture evaporation as the plant canopy serves as "living mulch." Space plants closely, seeing to it that each plant has enough sunshine and space to grow. Plants are correctly spaced when the leaves of the fully grown plants barely overlap with the adjacent ones. This achieves maximum use of space and higher yields per unit area, when compared with conventional gardening. Plant in a triangular fashion. The seeds or seedlings are planted at each end of an imaginary triangle, with the sides of the triangle being equal to the recommended spacing. This portion allows more plants to be grown within a small area than the usual method of square or row planting.

Two Methods of Planting

Row planting has more soil space exposed to sunlight which leads to rapid evaporation of soil moisture.

Thick canopy of plants reduces moisture evaporation and prevents weed growth.

Square planting

Triangular planting

Triangular method of planting gives more plants per unit area.

Using the fenceline for planting annual and perennial crops

Trees, shrubs and other crops must be planted in such a way that a multistoried cropping pattern is achieved. This way, various crops can-be grown in a limited space without competing with each other. Weed growth is also controlled through shading by the upper canopy level and by crawling vines.

Using the fenceline for planting annual and perennial crops

Upper canopy species (A) - form a protective canopy against tropical sun and torrential rains.

Middle canopy species (B) - feature staple and fruit production including trailing plants which can be allowed to climb the trees.

Lower canopy species (C) - bush-level growth which can be grown to form a double layer of protection against stray animals.

Understory crops and - shade-tolerant crops and crawling vines can be planted to further
creepers (D) cover the soil.

Purpose of Live Fence

1. protection against stray animals
2. windbreak
3. green manure
4. food
5. fuelwood
6. fodder

How to Make a Fenceline

1. Dig a trench 1 ½ ft. wide and 1 ½ ft. deep along the fence.
2. Mix the dug out soil with wood ash and compost and return the mixture into the trench.
3. Plant the seeds or cuttings.

Examples of Plants that Can Be Used in a Fence:

A. Upper Canopy Species
Moringa oleifera (horseradish tree)
Sesbania grandiflora (katuray)
Gliricidia septum (kakawate)
Averrhoa bilimbi (kamyas)
Psidium guajava (guava)
Persia americana (avocado)
Artocarpus altilis (breadfruit)
Artocarpus heterophyllus (jackfruit)
Annona muricata (soursop)
Annona squamosa (sugar apple)
Calliandra calothyrsus (calliandra)

B. Middle Canopy Species
Carica papaya (papaya)
Musa spp. (banana)
Citrus mitts (calamansi)
Flemingia macrophylla (flemingia)
Desmodium rensonii (rensonii)

Climbers
Psophocarpus tetragonolobus (winged bean)
Dioscorea alata (greater yam)
Dioscorea esculenta (lesser yam)
Pachyrrhizus erosus (yam bean)

C. Lower Canopy Species
Sauropus androgynus (Japanese malungay)
Corchorus olitorius (jute)
Capsicum frutescens (chili)
Manihot esculenta (cassava)
Cajanus cajan (pigeon pea)
Zea mays (corn)
Pandanus odoratissimus (pandan)
Maranta arundinacea (arrowroot)

D. Understory Crops and Creepers
Ananas comosus (pineapple)
Zingiber officinale (ginger)
Colocasia esculenta (taro)
Adropogon citratus (lemon grass)
Sesamum orientale (sesame)
Foeniculum vulgare (fennel)
Ipomoea batatas (sweet potato)
Ipomoea aquatica (swamp cabbage)
Basella alba (basella)

Reference:

Niņez, V. 1984. Household Gardens and Small-scale Food Production. Food and Nutrition Bulletin 7(3): 1-5

Companion plant guide chart

"Companion" plants have complementary physical and chemical demands. They will grow well together. "Antagonistic" plants have a negative effect on one another. Avoid planting them close to each other.

Vegetable	Companion	Antagonist
Abelmoschus esculentus (ladyfinger)	sweet potato, swamp cabbage, squash, radish, pechay (Brassica chinensis)
Allium cepa (onion)	lettuce, beets, tomato	peas, beans
Allium sativum (garlic)	carrot, lettuce, beets, tomato	peas, beans
Apium graveolens (celery)	cabbage family, tomato, bush bean
Asparagus officinale (asparagus)	tomato
Beta vulgaris (beets)	onion, garlic	pole beans
Brassicas (cabbage family)	potato, celery, beet, onion, garlic	pole beans
Colocasia esculenta (taro)	sweet potato, swamp cabbage
Cucumis sativus (cucumber)	corn, pole beans, ladyfinger, cowpea, radish, eggplant	potatoes
Cucurbita maxima (squash)	bottle gourd, sponge gourd, bitter gourd, cucumber
Ipomoea aquatica (swamp cabbage)	taro, sweet potato, cassava (Manihot esculenta), tomato, ladyfinger, corn, eggplant, amaranth (Amaranthus gracilis)
Ipomoea batatas (sweet potato) ladyfinger,	corn, cassava, eggplant, pigeon pea (Cajanus cajan)
Lactuca sativa (lettuce)	carrots, radish, cucumber
Lagenaria siceraria (bottle gourd)	sponge gourd, bitter gourd, cucumber
Luffa cylindrica (sponge gourd)	bottle gourd,
bitter gourd, cucumber
Lycopersicon Iycopersicum	onion, lettuce, sweet potato,	potato, cabbage
(tomato)	radish, swamp cabbage,
	squash, pechay, garlic, asparagus, carrots
Momordica charantia	lima bean (Phaseolus lunatus),
(bitter gourd)	hyacinth bean (Dolichos lablab),
	winged bean (Psophocarpus tetragonolobus),
	pole bean
Phaseolus aureus (mungbean)	corn, sorghum (Andropogon sorghum)
Phaseolus vulgaris (snap bean)	corn, carrot, cucumber, potato,	onion, garlic
	cabbage family
Raphanus sativus (radish)	beans, cucumber, lettuce
Solanum melongena (eggplant)	beans, lettuce,
sweet potato,
	swamp cabbage, squash, pechay,
	radish, pepper (Capsicum annuum)
Solanum tuberosum (potato)	garlic, beans, corn, cabbage	cucumber, tomato
Vigna sesquipedalis (pole bean)	corn	onion, beet
Vigna sinensis (bush bean)	potato, cucumber, corn, celery	onion

Vegetables that can be harvested in less than a month

Scientific Name	Common Names	No. of Days from Planting to
Harvesting
Brassica juncea	mustard	25
Brassica chinensis	pechay	25
Raphanus sativus	radish	20-25
Basella alba	basella	25
Amaranthus gracilis	amaranth	25-30
Ipomoea batatas	sweet potato	20
Ipomoea aquatica	swamp cabbage	20
Coriandrum sativum	coriander	15
Cucumis sativus	cucumber	30
Lactuca sativa	leaf lettuce	25
Portulaca oleracea	purslane	25
Talinum triangulare	Philippine spinach	25

Shade-tolerant vegetables

As plants are fitted together according to their various above-ground growth patterns, one should be aware of the plants' light and shade requirements so that they can benefit from the shade-light patterns and grow with minimum competition for light. Vegetables that grow best in the shade should be planted underneath larger ones.

Scientific Name	Common Name	Light Requirements
Zingiber officinale	ginger	requires about 50% shade
Colocasia esculenta	taro	tolerates up to 50% shade
Basella alba	basella	requires partial shade
Apium graveolens	celery	requires partial shade
Cucumis sativus	cucumber	requires partial shade
Lactuca sativa	lettuce	requires light shade
Brassica oleracea var. capitata	cabbage	requires light shade
Talinurn triangulare	Philippine spinach	tolerates light shade
Daucus carota	carrot	tolerates light shade
Solanum tuberosum	Irish potato	tolerates light shade

Drought-resistant vegetables

Scientific Name	Common Name	Degree of Resistance
Voandzeia subterranea	Bambara groundnut	highly drought-resistant
Tylosema esculentum	Marama bean	highly drought-resistant
Arachis hypogaea	peanut	highly drought-resistant
Vigna sesquipedalis	yardlong bean	highly drought-resistant
Cajanus cajan	pigeon pea	highly drought- and heat resistant once established
Abelmoschus esculentus	ladyfinger	fairly drought-resistant
Vigna aconitifolia	moth bean	most drought- tolerant crop grown in India
Sorghum bicolor	sorghum	highly drought-resistant
Vigna sinensis	cowpea	drought- and heat-toleran
Solanun melongena	eggplant	drought-tolerant
Manihot esculenta	cassava	drought-tolerant once established
Dolichos lablab	lablab bean	drought-tolerant once established
Phaseolus lunatus	lima bean	drought-tolerant once established
lpomoea batatas	sweet potato	fairly drought-tolerant
Amaranthus gracilis	amaranth	fairly drought-tolerant
Phaseolus aureus	mungbean	fairly drought-tolerant

Solarization: A weed control technique using sunlight

Solarization is a technique for killing weeds in a garden plot using the sun's heat. A clear plastic sheet is used to cover the garden plots and is then exposed to the heating rays of the sun for 10 - 15 days. This technique is used before the crops are planted and only when weeds are a serious problem and in the first year of starting a garden. Subsequently, garden practices such as yearround cultivation, crop rotation and intercropping should control weeds.

How to solarize:

1. Dig the garden bed to a depth of 20 - 30 cm, pulverize and level.

2. Water the surface to a depth of 15 - 20 cm.

3. Cover the entire surface of the garden with clear plastic (polyethylene).

4. Seal all sides by covering the edges of the plastic with soil or pieces of lumber/wood.

5. Keep the plastic in place for 10-15 days. During this period, the weed seeds will germinate and, through the intense heat of the sun, will gradually be killed.

6. Remove the plastic cover.

7. Apply compost and other soil supplements and incorporate into the soil to a depth of 10 15 cm.

8. Level the garden bed and plant.

How to solarize

* Water buffalo, cow and horse manures, if applied directly (even in dried form). can result in increased weed growth due to the presence of weed seeds in the excreta. If such uncomposted manure is used, it should be incorporated into the soil before the plastic cover is placed onto the bed. Weed seeds are not generally found in pig and Poultry manures.

Watering

One of the most critical factors for successful gardening is water. Poor watering practices can stunt plant growth and can even be fatal to plants. As a rule, plants should be watered thoroughly but infrequently. Thorough watering dampens the soil. This allows the water to move down through the soil by progressively satisfying the waterholding capacity of every soil particle. Likewise, well-sequenced watering allows the water to sink slowly and the soil surface to dry up. These conditions encourage the development of a deep root system.

Well Sequenced Watering

Too Frequent Watering

Plants are deep-rooted and can withstand drought periods because they rely on subsoil water.

Plants are shallow-rooted and suffer with even a slight reduction in moisture availability; plants become dependent on applied water.

Note: This does not apply to young plants (i.e., less than 40 days old), which need daily watering in dry weather.

Mulching

Mulch is loose organic materials, such as straw, cut grass, leaves and the like used to cover the soil around the plants or between the rows for protection or improvement of the area covered. A mulch aids in maintaining a favorable condition of the soil underneath. The increased plant growth is due primarily to conditions resulting from the use of a given material rather than any growth promoting substances present in the mulch itself.

Since organic mulches are derived from plant materials, decomposition will occur and this has several positive effects on both the soil and the plants.

Mulching

Physical Effects

1. If mixed in the upper soil layer, the material dilutes the soil and usually increases root growth. Aeration and water-holding capacity are increased on clay and sandy soils, respectively.

2. During the decomposition of the organic material, soil microorganisms secrete a sticky material which promotes the granulation or clinging together of the soil.

3. Mulch improves and stabilizes soil structure or the arrangement of soil particles. It serves as a cushion, reducing soil compaction caused by pelting rain, coarse streams or drops of water from irrigation devices.

Chemical Effects

1. Most organic materials will raise the soil pH slighty, making it more alkaline. This can be remedied by mixing acid-forming or organic matter like sawdust and moss peat with the soil.

2. In two or three months, mulch rots and small amounts of fertilizer become available to the plants.

3. Nitrogen deficiency may become apparent with mulched plants because an appreciable amount of nitrogen is taken from the soil by the microorganisms decomposing the organic mulch. To avoid this, liquid fertilizer must be applied to the plant as nitrogen-supplement .

Biological Effects

1. Organic mulch serves as food for many microorganisms found in the soil. It also helps keep the temperature more constant so microorganisms activity can proceed at a uniform rate.

2. Sometimes undesirable organisms like disease-causing fungi, bacteria and nematodes may be added to the soil with the application of organic plant materials. Stirring the mulch occasionally eliminates the mold. During rainy season, mulch should be applied only when the plants are at least a month old to deter pest attack.

3. Weed seeds may be introduced into the garden with hay or straw. This can be avoided by using only the middle portion of the plant as mulching material. The flowers and the roots must first be composted.

Without mulch, weeds are growing in between plants.

Mulch prevents the growth of weed.

Mulching prevents soil compaction.

The role of organic mulches

Mulches have many beneficial effects upon the soil, plants and area surrounding the plants.

1. They conserve soil moisture by reducing evaporation of water from the soil.

2. They prevent crusting of the soil surface, thus improving absorption and percolation of water to the soil areas where the roots are growing.

3. They maintain a more uniform soil temperature by acting as an insulator that keeps the soil warm during cool spells and cooler during the warm months of the year.

4. They prevent fruits and plants from becoming mud splashed and reduce losses from soil-borne diseases.

5. They reduce weed problems when the mulch material itself is weed-free and is applied deep enough (at least 2.5-cm thick) to prevent weed seed germination or smother existing smaller weeds. Time and labor of weeding is reduced considerably when mulches are used properly.

The role of organic mulches

Some tropical materials for use as mulch

	Nitrogen	Phosporus	Potash
Corn cobs	x	x	xxx
Corn silage	x	x	x
Corn stalks	x	x	x
Rice straw	xx	x	x
Rice bran	xx	x	x
Wheat straw	xx	x	x
Wheat bran	xx	x	x
Peanut shells	x	x	x
Egg shells	x	x	x
Feathers	xxx	x	x
Sugar by-products	x	xxx	x
Coffee grounds	x	x	x
Tea grounds	xx	x	x
Seaweed	xx	x	x
Fish bones	xx	xx	xx
Banana stalk	x	xx	xxx
Banana skins	x	xx	xxx
Banana leaves	x	xx	xxx
Tobacco leaves	xx	x	xx
Tobacco stalk	xx	x	xx

xxx - Good source
xx - Fair source
x - Poor source

References:

Brooks, W. M., J.D. Utzinger and H. R. Tayama. (Undated). Mulches for the Home Grounds. Ohio State University.

Gardening in dry environments

Some of the problems associated with dry-land gardening are light saturation and excessive evaporation, which can lead to more serious problems like nutrient deficiency and soil alkalinity. These problems can greatly affect the growth and development of plants. But, gardening is still possible under such conditions if a special environment is created.

1. Deep digging. This improves soil structure, making it more porous. With more spaces in the soil, greater amounts of water can be stored for the use of the plants.

2. Addition of large amounts of organic matter into the soil. While nutrients can be present in dryland soils, they are usually chemically unavailable due to high soil pH. Organic matter is essential to create humus, which can make the elements become available to the plants. It also acts like a sponge, absorbing water so that less evaporates.

3. Close spacing of plants. With all available spaces filled up with plants, there is less exposure of soil to direct sunlight; hence, less evaporation. Shading of the soil also keeps down weeds, another competitor for water.

4. Provision of windbreaks. Growing trees around the garden helps to lower the temperature in the immediate vicinity of the garden and deflects dry winds. It, therefore, decreases water loss from the plant surfaces.

5. Clay pot technique. Water in a clay pot buried in the soil will diffuse slowly from the pot to the plants:

a. Sink unglazed, porous clay pots into the beds (with the opening just above the bed surface) one meter apart. Fill with water and cover to reduce direct evaporation.

b. Add a thin layer (0.5 cm) of straw or grass clippings as mulch.

c. When the plants are about three weeks old, add more mulch (5 - 8 cm).

Close spacing of plants

Clay pot technique

Water-saving ideas for gardens during dry season

Conserving water is especially important during dry months when water is limited. However, water conservation does not necessarily mean cutting down on water, rather, it means making the most of available water.

1. Water early in the morning. Watering in the morning allows greater absorption of water by the soil. Later in the day, the air is hot and dry and water evaporates from the soil surface faster.

2. Water placement. The best method of watering is by trickle or drip irrigation with a perforated plastic hose placed adjacent to each crop row. This puts the water exactly where it is needed.

3. Mulch. Mulch helps retain moisture by reducing surface evaporation. It also prevents weed growth and builds up humus, improving the water-holding capacity of the soil.

4. Weed regularly. Undesirable plants should not be allowed to have a share of any available water.

5. Select adapted plants. Use plants with a low water need, a deep root system and which tolerate heat and drought. Cucurbits, beans and some grains are good examples of plants that can be grown with little water.

6. Recycle water. Any water from household uses (must be low in detergents and grease) can be saved and used in the garden.

Water-saving ideas for gardens during dry season

References:

Ameroso, L. (Undated). Plan Now to Conserve Water In Your Garden. Cornell Cooperative Extension, New York City Gardening Program.

Mollison, B. and R. M. Slay. 1991. Introduction to Permaculture. Tagari Publications, Australia. 198 pp.

Growing vegetables in saline areas

Saline soils are soils that have been harmed by excessive amounts of soluble salts - mainly sodium, calcium, magnesium, chloride and sulfate, as well as potassium, bicarbonate, carbonate, nitrate and boron. The abnormally high salt concentration of saline soils reduces the rate at which plants absorb water, consequently growth is retarded. Aside from growth retardation of plants, certain salt constituents, like boron, are specifically toxic to some crops.

What Causes Soil Salinity?

1. Lack of water. Salt-affected soils are common in arid or semiarid regions because there is less rainfall available to leach and transport the salts and because the high evaporation and plant transpiration rates in arid climates tend to further concentrate the salts in soils and surface waters.

2. Poor drainage. When water table rises to within 1.5 or 2 m of the surface, groundwater containing dissolved salt moves upward into the root zone and to the soil surface. Groundwater then causes the soil to become saline.

3. Excessive irrigation. Irrigation waters may contain large amount of salt. Considerable quantities of soluble salts may be added to irrigated soils in a short time.

What Causes Soil Salinity

How to Tell if your Soil is Affected by Salinity

The salinity status of soils is appraised by measuring electrical conductivity of the solution extracted from saturated soil paste. The yields of very salt-sensitive crops may be restricted at readings as low as 2, moderately salt-tolerant crops grow satisfactorily below readings of 8; only salt-tolerant crops grow satisfactorily when readings range between 8 and 16.

Management Practices for the Control of Salinity

1. Select crops or crop cultivars that can grow successfully under saline conditions. Among the highly tolerant vegetables are beets, kale, asparagus, spinach and tomato.

2. Use land preparation and tillage methods that aid in the control of salinity. Careful leveling of land makes possible a more uniform application of water and better salinity control.

3. Modify watering practices and bed shape to alter the of salts to accumulate near the seed. Pre-emergence watering in special furrows placed close to the seed often is done to reduce the soluble salt concentration around the seeds and thus permit germination. After the seedlings are established, the special furrows may be abandoned and new furrows made between the rows.

4. Use special planting procedures that minimize salt accumulation around the seed. The tendency of salts to accumulate near the seed during irrigation is greatest in single-row, flattopped beds. With double-row beds, most of the salt is carried into the center of the bed, leaving the shoulders relatively free of salt and satisfactory for planting.

Standard vegetable bed' for saline soils

For peppers chile, ladyfinger, sweet potatoes, cowpeas and sweet corn

5. Water properly, so as to maintain a relatively high soil moisture level and, at the same time, allow for periodic leaching of the soil and reduce salinity problems. The method and frequency of watering and the amount of water applied are of prime importance in the control of salinity. The amount of water applied should be sufficient to supply the crop and satisfy the leaching requirement but not enough to overload the system.

6. "Pond" water over the entire soil surface to make leaching efficient. Soils can be leached by applying water to the surface and allowing it to pass downward through the root zone.

7. Apply special treatments, such as, adding organic matters and growing sod crops to improve soil structure. Low permeability of the soil causes poor drainage by impeding the downward movement of water. The impedance may be the result of an unfavorable increase in groundwater level, which then causes the soil to become saline.

Reference:

Bower, C. A. and M. Fireman. 1957. Saline and Alkali Sails. In Yearbook of Agriculture by USDA, Washington, D. C.

Lead in urban gardens

URBAN gardens are often affected by the presence of metal pollutants in the air and on the soil. Air pollution can cause health problems for humans and can retard plant growth.

Of the metal pollutants, lead is a major concern. At least two sources of lead affect city grown produce: gasoline emissions and lead-based paint. Lead can be deposited directly on the plant leaves or on the soil. Lead in the soil is usually not taken up by plant roots unless it is present in large quantities. Soil-borne lead is rarely found in the fruiting parts of the plants. It is found mostly in the roots and leaves.

A number of factors affect the amount of soil-borne lead found in plants. Plants growing in soils with high organic matter content take up small amounts of lead. Decomposed organic matter and well-rotted manure tend to bind the lead and makes it insoluble to plant roots. If the soil pH is kept between 6.5 and 7.0, lead uptake can be reduced. Soil pH levels above 6.5 also reduce the absorption of metallic cadmium, another dangerous pollutant. Applying 8 - 10 cm of well-decomposed compost to each bed and incorporate it in the soil helps reduce lead uptake.

A bigger concern in lead-contaminated gardens comes from the exposure of children to the soil. Young children playing in the garden may put soil in their mouths, ingesting the lead. This method of lead poisoning is more common than through "consuming lead-polluted vegetables. Avoid taking young children into urban gardens to reduce their direct exposure to surface soil lead.

Fortunately, lead deposits on leaves can easily be washed off. Water alone is not sufficient. Wash with diluted vinegar (1% or one spoonful of vinegar in 100 spoons of water) or diluted dish washing liquid (0.5% or half a spoonful for every 100 spoons of water) is preferred. Root crops should be peeled to ensure that lead adhering to the skin is removed. Since green leafy vegetables are most affected by lead deposits, they should be planted as far away as possible from roads with heavy traffic.

Vegetables such as tomatoes, eggplants, beans, squash and peppers should be planted closer to the roads since they show lower concentrations of the metals. However, at least 10 meters should separate any garden from the street. Barrier crops such as a hedge planted at the side of the garden facing the road can effectively reduce the deposit of lead and other metals on garden produce and on the soil itself.

The problem of lead pollution in urban gardens can be addressed by the following measures:

Apply high quantities of organic matter to the soil.
Cultivate root and fruiting vegetables.
If you grow leafy vegetables, plant them away from the source of lead emissions.
Wash vegetables with diluted soap or vinegar.
Keep very young children away from lead-polluted gardens.

Reference:

Bassuk, N. L. 1983. Lead in Urban (frown Vegetables. Cornell University.